Re: [BUG] [PATCH v2 1/2] clocksource: arm_global_timer: implement rate compensation whenever source clock changes

From: Johan Jonker
Date: Sun Oct 30 2022 - 11:09:12 EST

Hi,

Let me know what more data you like?
Function gt_clk_rate_change_cb() generates only errors.

Johan

On 10/30/22 15:50, Johan Jonker wrote:
> Hi Andrea,
>
> Some MK80 rk3066a details:
> From rk3xxx.dtsi:
>
> global_timer: global-timer@1013c200 {
> compatible = "arm,cortex-a9-global-timer";
> reg = <0x1013c200 0x20>;
> interrupts = <GIC_PPI 11 (GIC_CPU_MASK_SIMPLE(2) | IRQ_TYPE_EDGE_RISING)>;
> clocks = <&cru CORE_PERI>;
> };
>
> ===
>
> rk3066a clk_summery:
> enable prepare protect duty hardware
> clock count count count rate accuracy phase cycle enable
> -------------------------------------------------------------------------------------------------------
> xin24m 8 8 0 24000000 0 0 50000 Y
> pll_apll 1 1 0 1416000000 0 0 50000 Y
> apll 1 1 0 1416000000 0 0 50000 Y
> armclk 2 2 0 1416000000 0 0 50000 Y

divider 1:

DivFree
1~32

===

divider 2:

Divider can be Div
2,4,8,16
mux

Does that tree match with this prescaler patch?

> core_peri 2 2 0 177000000 0 0 50000 Y
>
> ===
>
> Before your patch:
>
> [ 0.000000] >>>> GT gt_clk_rate:75000000
> [ 0.000000] >>>> GT gt_clocksource_init ctrl :00000001
>
> [ 0.000105] >>>> GT gt_clockevent_shutdown ctrl:00000001
> [ 0.000128] >>>> GT gt_compare_set delta :750000
> [ 0.000143] >>>> GT gt_compare_set ctrl :0000000f
> [ 0.000412] >>>> GT gt_clockevent_shutdown ctrl:00000001
> [ 0.000444] >>>> GT gt_clockevent_shutdown ctrl:00000001
>
> ===
>
> After your patch with prescaler 1:

Copy went wrong. Should have been example for prescaler 1.
>
> [ 0.000000] >>>> GT CONFIG_ARM_GT_INITIAL_PRESCALER_VAL:2

> [ 0.000000] >>>> GT gt_clk_rate :75000000
> [ 0.000000] >>>> GT gt_target_rate :37500000

[ 0.000000] >>>> GT gt_clk_rate :75000000
[ 0.000000] >>>> GT gt_target_rate :75000000



> [ 0.000000] >>>> GT gt_clocksource_init ctrl :00000101
> [ 0.000002] sched_clock: 64 bits at 38MHz, resolution 26ns, wraps every 2199023255540ns
> [ 0.000049] clocksource: arm_global_timer: mask: 0xffffffffffffffff max_cycles: 0x8a60dd6a9, max_idle_ns: 440795204056 ns
> [ 0.000104] >>>> GT gt_clockevent_shutdown ctrl:00000101
> [ 0.000129] >>>> GT gt_compare_set delta :375000
> [ 0.000143] >>>> GT gt_compare_set ctrl :0000010f
> [ 0.000175] Switching to timer-based delay loop, resolution 26ns
> [ 0.000396] >>>> GT gt_clockevent_shutdown ctrl:00000101
> [ 0.000428] >>>> GT gt_clockevent_shutdown ctrl:00000101
> [ 0.001785] clocksource: timer: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 79635851949 ns
> [ 0.002136] Ignoring duplicate/late registration of read_current_timer delay
>
> [ 13.783289] calling dt_cpufreq_platdrv_init+0x0/0x28 @ 1

> [ 13.809106] >>>> GT gt_clk_rate_change_cb ndata->new_rate:78000000
> [ 13.809148] >>>> GT gt_clk_rate_change_cb gt_target_rate :37500000


[ 13.832554] >>>> GT gt_clk_rate_change_cb ndata->new_rate:78000000
[ 13.832596] >>>> GT gt_clk_rate_change_cb gt_target_ratem:75000000

These rates don't match.

> [ 13.833691] >>>> GT gt_clk_rate_change_cb psv 1 :2
> [ 13.857882] >>>> GT gt_clk_rate_change_cb MAX_F_ERR :50
> [ 13.884605] >>>> GT gt_clk_rate_change_cb abs(gt_target_rate - (ndata->new_rate / psv)):1500000

The differance is larger then MAX_F_ERR.

> [ 13.911207] >>>> GT NOTIFY_BAD 1

Result is NOTIFY_BAD.

> [ 13.938409] >>>> GT gt_write_presc psv:0
> [ 13.959266] >>>> GT gt_write_presc reg:00000001
> [ 13.980873] cpu cpu0: _opp_config_clk_single: failed to set clock rate: -16
> [ 14.074809] cpufreq: __target_index: Failed to change cpu frequency: -16
> [ 14.124490] ------------[ cut here ]------------
> [ 14.168380] kernel BUG at drivers/cpufreq/cpufreq.c:1480!
>
> ===
>
> After your patch with prescaler 2:
>
> [ 0.000000] >>>> GT CONFIG_ARM_GT_INITIAL_PRESCALER_VAL:2
> [ 0.000000] >>>> GT gt_clk_rate :75000000
> [ 0.000000] >>>> GT gt_target_rate :37500000
> [ 0.000000] >>>> GT gt_clocksource_init ctrl :00000101
> [ 0.000002] sched_clock: 64 bits at 38MHz, resolution 26ns, wraps every 2199023255540ns
> [ 0.000049] clocksource: arm_global_timer: mask: 0xffffffffffffffff max_cycles: 0x8a60dd6a9, max_idle_ns: 440795204056 ns
> [ 0.000104] >>>> GT gt_clockevent_shutdown ctrl:00000101
> [ 0.000129] >>>> GT gt_compare_set delta :375000
> [ 0.000143] >>>> GT gt_compare_set ctrl :0000010f
> [ 0.000175] Switching to timer-based delay loop, resolution 26ns
> [ 0.000396] >>>> GT gt_clockevent_shutdown ctrl:00000101
> [ 0.000428] >>>> GT gt_clockevent_shutdown ctrl:00000101
> [ 0.001785] clocksource: timer: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 79635851949 ns
> [ 0.002136] Ignoring duplicate/late registration of read_current_timer delay
>
> [ 13.783289] calling dt_cpufreq_platdrv_init+0x0/0x28 @ 1
> [ 13.809106] >>>> GT gt_clk_rate_change_cb ndata->new_rate:78000000
> [ 13.809148] >>>> GT gt_clk_rate_change_cb gt_target_rate :37500000
> [ 13.833691] >>>> GT gt_clk_rate_change_cb psv 1 :2
> [ 13.857882] >>>> GT gt_clk_rate_change_cb MAX_F_ERR :50
> [ 13.884605] >>>> GT gt_clk_rate_change_cb abs(gt_target_rate - (ndata->new_rate / psv)):1500000
> [ 13.911207] >>>> GT NOTIFY_BAD 1
> [ 13.938409] >>>> GT gt_write_presc psv:0
> [ 13.959266] >>>> GT gt_write_presc reg:00000001
> [ 13.980873] cpu cpu0: _opp_config_clk_single: failed to set clock rate: -16
> [ 14.074809] cpufreq: __target_index: Failed to change cpu frequency: -16
> [ 14.124490] ------------[ cut here ]------------
> [ 14.168380] kernel BUG at drivers/cpufreq/cpufreq.c:1480!
>
> On 10/27/22 15:37, Andrea Merello wrote:
>> Il giorno lun 17 ott 2022 alle ore 10:03 Johan Jonker
>> <jbx6244@xxxxxxxxx> ha scritto:
>>>
>>> Hi Andrea,
>>>
>>> Your patch contribution causes a kernel panic on MK808 with Rockchip rk3066a SoC.
>>> Would you like to contribute to fix this issue?
>>
>> Hi! Thank you for reporting this; I'm definitely interested in
>> investigating this issue.
>>
>>> The psv variable divides with 0 and more things might be wrong.
>>> A revert makes it work again.
>>
>> Hum, good point: it's probably worth adding a check in the LOC you
>> pointed out and eventually returning NOTIFY_BAD.. Note however that
>> this would prevent the division by zeroed-psv (which is really
>> desirable), but it wouldn't make all magically work - so it's probably
>> worth understanding what's happening.. :
>>
>> I'm not familiar with your SoC; is it like the Zynq i.e. when enabling
>> cpu frequency scaling then the clock source feeding the ARM global
>> timer keeps changing rate? If the rate-change callback has run (and it
>> calculated a zero psv) then it seems the case.
>>
>> If this is really the case, then I'd say that the frequency scaling
>> needed to be disabled (i.e. locked out) when the ARM global timer was
>> in use without my patch (otherwise your clocksource would be also
>> unstable), while to take advantage of my patch a reasonable
>> CONFIG_ARM_GT_INITIAL_PRESCALER_VAL should be set (and hopefully this
>> prevents psv to become zero).
>>
>> IOW, in this case, I would expect KConfig not letting enabling
>> frequency scaling and ARM global timer together (IIRC that was what
>> Zynq did) in case my patch is not there, or otherwise defining at
>> least a good default value for CONFIG_ARM_GT_INITIAL_PRESCALER_VAL,
>> that make it possible to swing the prescaler in a range wide enough.
>>
>> How's CONFIG_ARM_GT_INITIAL_PRESCALER_VAL set in your kernel
>> configuration? Maybe tweaking with it prevents the problem?
>>
>> On the contrary, in case your SoC doesn't vary the ARM global timer
>> clock source when scaling CPU frequency, then I don't understand why
>> the rate-change notification callback, where the psv is calculated, is
>> ever called (although I admit that I'm starting to wonder whether it
>> is maybe called one time anyway).. But even if it is, then the clock
>> rate should be the very same, so I would expect the psv to be
>> calculated as non-zero anyway.. Or am I missing some case in which
>> approximations can lead to zero?
>>
>> BTW I'm not really sure about what's going on here: I cannot directly
>> correlate the Oops you attached below to the LOC you pointed out. How
>> did you track down the problem to that?
>>
>> Thanks
>> Andrea
>>
>>>
>>> Johan
>>>
>>> =====
>>>
>>> [ 13.087809] ------------[ cut here ]------------
>>> [ 13.110701] kernel BUG at drivers/cpufreq/cpufreq.c:1480!
>>> [ 13.134378] Internal error: Oops - BUG: 0 [#1] SMP ARM
>>> [ 13.157793] Modules linked in:
>>> [ 13.178760] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 6.0.0-next-20221013 #1
>>> [ 13.205990] Hardware name: Rockchip (Device Tree)
>>> [ 13.228793] PC is at cpufreq_online+0x8fc/0xa1c
>>> [ 13.251421] LR is at __wake_up_common_lock+0x98/0xc4
>>> [ 13.274536] pc : [<c06883d8>] lr : [<c0171c50>] psr: a0000013
>>> [ 13.299046] sp : f0821c50 ip : f0821b70 fp : f0821c9c
>>> [ 13.322445] r10: 00000000 r9 : 00000000 r8 : c0f9b800
>>> [ 13.345887] r7 : 000493e0 r6 : c115ef18 r5 : c1005058 r4 : c2055e00
>>> [ 13.370714] r3 : b4aeb193 r2 : b4aeb193 r1 : 60000013 r0 : fffffff0
>>> [ 13.395373] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
>>> [ 13.420948] Control: 10c5387d Table: 6000404a DAC: 00000051
>>> [ 13.444914] Register r0 information: non-paged memory
>>> [ 13.468230] Register r1 information: non-paged memory
>>> [ 13.491289] Register r2 information: non-paged memory
>>> [ 13.514135] Register r3 information: non-paged memory
>>> [ 13.536767] Register r4 information: slab kmalloc-512 start c2055e00 pointer offset 0 size 512
>>> [ 13.563712] Register r5 information: non-slab/vmalloc memory
>>> [ 13.587158] Register r6 information: non-slab/vmalloc memory
>>> [ 13.610385] Register r7 information: non-paged memory
>>> [ 13.632699] Register r8 information: non-slab/vmalloc memory
>>> [ 13.655529] Register r9 information: NULL pointer
>>> [ 13.677204] Register r10 information: NULL pointer
>>> [ 13.698865] Register r11 information: 2-page vmalloc region starting at 0xf0820000 allocated at kernel_clone+0xc0/0x3b0
>>> [ 13.727678] Register r12 information: 2-page vmalloc region starting at 0xf0820000 allocated at kernel_clone+0xc0/0x3b0
>>> [ 13.756320] Process swapper/0 (pid: 1, stack limit = 0x(ptrval))
>>> [ 13.779523] Stack: (0xf0821c50 to 0xf0822000)
>>> [ 13.800858] 1c40: 00000000 00000001 ef7c5050 00000001
>>> [ 13.826719] 1c60: c10da900 00000002 c115ef18 c2055f20 c0942224 00000000 ef7c5050 c1004ec8
>>> [ 13.852544] 1c80: c20d7b40 c10da884 c1005058 c1004f14 f0821cb4 f0821ca0 c0688590 c0687ae8
>>> [ 13.878330] 1ca0: c10da570 c10cf8a8 f0821ce4 f0821cb8 c0595080 c0688524 c14f7958 c1645434
>>> [ 13.904232] 1cc0: 00000000 b4aeb193 00000060 c10da900 c115ef18 c10da434 f0821d0c f0821ce8
>>> [ 13.930231] 1ce0: c06859e0 c0594fdc c10da8ec ef7c5050 c20d7b40 00000002 c10da8ec ef7c5050
>>> [ 13.956321] 1d00: f0821d8c f0821d10 c068b9a4 c068589c c0b161cc c1004ec8 00000000 c0b7b718
>>> [ 13.982392] 1d20: c14e3400 00000000 c20d7b48 00000001 c033f608 c20da5d8 c20da688 c160c688
>>> [ 14.008446] 1d40: c0b8bd28 00000001 c0c47d54 c111b000 f0821d84 00000000 00000000 b4aeb193
>>> [ 14.034637] 1d60: c14e3410 c14e3410 00000000 c10da898 00000000 c20d7ab8 c0c47d54 c111b000
>>> [ 14.060896] 1d80: f0821dac f0821d90 c0599424 c068b68c c14e3410 00000000 c10da898 00000000
>>> [ 14.087313] 1da0: f0821dcc f0821db0 c0596cd0 c05993c4 c14e3410 c10da898 c14e3410 00000000
>>> [ 14.113601] 1dc0: f0821de4 f0821dd0 c0596f8c c0596c04 c115dd68 c14e3410 f0821e04 f0821de8
>>> [ 14.139950] 1de0: c0596fe8 c0596ec0 00000000 c14e3410 c10da898 c059741c f0821e2c f0821e08
>>> [ 14.166351] 1e00: c0597490 c0596fb4 c1546ab4 c1004ec8 c10da898 c059741c c20d7ab8 c0c47d54
>>> [ 14.192790] 1e20: f0821e5c f0821e30 c0594c2c c0597428 f0821e68 c14f7858 c1546ab4 b4aeb193
>>> [ 14.219273] 1e40: c10da898 c10cf808 c20d7a80 00000000 f0821e6c f0821e60 c0596528 c0594bb4
>>> [ 14.245875] 1e60: f0821e9c f0821e70 c0595e60 c0596508 c0b7b7c8 00000000 f0821e9c c10da898
>>> [ 14.272550] 1e80: c1004ec8 c0c28e84 00000000 c1456854 f0821eb4 f0821ea0 c0597c80 c0595cc0
>>> [ 14.299270] 1ea0: c110cec0 c1004ec8 f0821ec4 f0821eb8 c0599130 c0597c08 f0821ed4 f0821ec8
>>> [ 14.326125] 1ec0: c0c28ea8 c0599110 f0821f4c f0821ed8 c0102180 c0c28e90 c03318e4 c0b14f30
>>> [ 14.352912] 1ee0: c0b14f10 c0b14f00 c0b2bc78 c1004ec8 00000000 c0b855d0 00000006 00000006
>>> [ 14.379805] 1f00: 00000000 c0b76eb0 c0c0055c c0bebf78 c0953a9c c154665b 00000000 b4aeb193
>>> [ 14.406665] 1f20: c0181cb8 b4aeb193 000000c6 c0c82160 00000007 c0c47d34 c1546600 000000c6
>>> [ 14.433661] 1f40: f0821f94 f0821f50 c0c01a48 c0102134 00000006 00000006 00000000 c0c0055c
>>> [ 14.460621] 1f60: c0c0055c c0bebf78 c1588000 00004ec0 c096ea48 00000000 00000000 00000000
>>> [ 14.487681] 1f80: 00000000 00000000 f0821fac f0821f98 c096ea6c c0c01884 00000000 c096ea48
>>> [ 14.514695] 1fa0: 00000000 f0821fb0 c0100148 c096ea54 00000000 00000000 00000000 00000000
>>> [ 14.541771] 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>>> [ 14.568615] 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
>>> [ 14.595194] Backtrace:
>>> [ 14.615207] cpufreq_online from cpufreq_add_dev+0x78/0x84
>>> [ 14.638819] r10:c1004f14 r9:c1005058 r8:c10da884 r7:c20d7b40 r6:c1004ec8 r5:ef7c5050
>>> [ 14.665198] r4:00000000
>>> [ 14.685514] cpufreq_add_dev from subsys_interface_register+0xb0/0xfc
>>> [ 14.710558] r5:c10cf8a8 r4:c10da570
>>> [ 14.732076] subsys_interface_register from cpufreq_register_driver+0x150/0x2d8
>>> [ 14.758094] r6:c10da434 r5:c115ef18 r4:c10da900
>>> [ 14.780943] cpufreq_register_driver from dt_cpufreq_probe+0x324/0x49c
>>> [ 14.806283] r6:ef7c5050 r5:c10da8ec r4:00000002
>>> [ 14.829299] dt_cpufreq_probe from platform_probe+0x6c/0xc8
>>> [ 14.853499] r10:c111b000 r9:c0c47d54 r8:c20d7ab8 r7:00000000 r6:c10da898 r5:00000000
>>> [ 14.880388] r4:c14e3410
>>> [ 14.901252] platform_probe from really_probe+0xd8/0x2bc
>>> [ 14.925473] r7:00000000 r6:c10da898 r5:00000000 r4:c14e3410
>>> [ 14.949898] really_probe from __driver_probe_device+0xd8/0xf4
>>> [ 14.974546] r7:00000000 r6:c14e3410 r5:c10da898 r4:c14e3410
>>> [ 14.998855] __driver_probe_device from driver_probe_device+0x40/0xd0
>>> [ 15.024426] r5:c14e3410 r4:c115dd68
>>> [ 15.046857] driver_probe_device from __driver_attach+0x74/0x120
>>> [ 15.072380] r7:c059741c r6:c10da898 r5:c14e3410 r4:00000000
>>> [ 15.097388] __driver_attach from bus_for_each_dev+0x84/0xc4
>>> [ 15.122444] r9:c0c47d54 r8:c20d7ab8 r7:c059741c r6:c10da898 r5:c1004ec8 r4:c1546ab4
>>> [ 15.150131] bus_for_each_dev from driver_attach+0x2c/0x30
>>> [ 15.175532] r7:00000000 r6:c20d7a80 r5:c10cf808 r4:c10da898
>>> [ 15.201134] driver_attach from bus_add_driver+0x1ac/0x1f8
>>> [ 15.226772] bus_add_driver from driver_register+0x84/0x11c
>>> [ 15.252559] r8:c1456854 r7:00000000 r6:c0c28e84 r5:c1004ec8 r4:c10da898
>>> [ 15.279483] driver_register from __platform_driver_register+0x2c/0x34
>>> [ 15.306523] r5:c1004ec8 r4:c110cec0
>>> [ 15.329801] __platform_driver_register from dt_cpufreq_platdrv_init+0x24/0x28
>>> [ 15.357500] dt_cpufreq_platdrv_init from do_one_initcall+0x58/0x20c
>>> [ 15.384159] do_one_initcall from kernel_init_freeable+0x1d0/0x22c
>>> [ 15.410635] r8:000000c6 r7:c1546600 r6:c0c47d34 r5:00000007 r4:c0c82160
>>> [ 15.437567] kernel_init_freeable from kernel_init+0x24/0x144
>>> [ 15.463573] r10:00000000 r9:00000000 r8:00000000 r7:00000000 r6:00000000 r5:c096ea48
>>> [ 15.491869] r4:00004ec0
>>> [ 15.514022] kernel_init from ret_from_fork+0x14/0x2c
>>> [ 15.539079] Exception stack(0xf0821fb0 to 0xf0821ff8)
>>> [ 15.563943] 1fa0: 00000000 00000000 00000000 00000000
>>> [ 15.592459] 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>>> [ 15.620836] 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
>>> [ 15.647222] r5:c096ea48 r4:00000000
>>> [ 15.670196] Code: e1a00004 ebfff74d e3500000 0a00001a (e7f001f2)
>>> [ 15.696086] ---[ end trace 0000000000000000 ]---
>>> [ 15.720522] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>>> [ 15.748404] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---
>>>
>>>
>>> On 4/6/21 15:00, Andrea Merello wrote:
>>>> This patch adds rate change notification support for the parent clock;
>>>> should that clock change, then we try to adjust the our prescaler in order
>>>> to compensate (i.e. we adjust to still get the same timer frequency).
>>>>
>>>> This is loosely based on what it's done in timer-cadence-ttc. timer-sun51,
>>>> mips-gic-timer and smp_twd.c also seem to look at their parent clock rate
>>>> and to perform some kind of adjustment whenever needed.
>>>>
>>>> In this particular case we have only one single counter and prescaler for
>>>> all clocksource, clockevent and timer_delay, and we just update it for all
>>>> (i.e. we don't let it go and call clockevents_update_freq() to notify to
>>>> the kernel that our rate has changed).
>>>>
>>>> Note that, there is apparently no other way to fixup things, because once
>>>> we call register_current_timer_delay(), specifying the timer rate, it seems
>>>> that that rate is not supposed to change ever.
>>>>
>>>> In order for this mechanism to work, we have to make assumptions about how
>>>> much the initial clock is supposed to eventually decrease from the initial
>>>> one, and set our initial prescaler to a value that we can eventually
>>>> decrease enough to compensate. We provide an option in KConfig for this.
>>>>
>>>> In case we end up in a situation in which we are not able to compensate the
>>>> parent clock change, we fail returning NOTIFY_BAD.
>>>>
>>>> This fixes a real-world problem with Zynq arch not being able to use this
>>>> driver and CPU_FREQ at the same time (because ARM global timer is fed by
>>>> the CPU clock, which may keep changing when CPU_FREQ is enabled).
>>>>
>>>> Signed-off-by: Andrea Merello <andrea.merello@xxxxxxxxx>
>>>> Cc: Patrice Chotard <patrice.chotard@xxxxxx>
>>>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>>>> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>>>> Cc: Michal Simek <michal.simek@xxxxxxxxxx>
>>>> Cc: Sören Brinkmann <soren.brinkmann@xxxxxxxxxx>
>>>> ---
>>>> drivers/clocksource/Kconfig | 13 +++
>>>> drivers/clocksource/arm_global_timer.c | 122 +++++++++++++++++++++++--
>>>> 2 files changed, 125 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>>>> index 39aa21d01e05..19fc5f8883e0 100644
>>>> --- a/drivers/clocksource/Kconfig
>>>> +++ b/drivers/clocksource/Kconfig
>>>> @@ -358,6 +358,19 @@ config ARM_GLOBAL_TIMER
>>>> help
>>>> This option enables support for the ARM global timer unit.
>>>>
>>>> +config ARM_GT_INITIAL_PRESCALER_VAL
>>>> + int "ARM global timer initial prescaler value"
>>>> + default 1
>>>> + depends on ARM_GLOBAL_TIMER
>>>> + help
>>>> + When the ARM global timer initializes, its current rate is declared
>>>> + to the kernel and maintained forever. Should it's parent clock
>>>> + change, the driver tries to fix the timer's internal prescaler.
>>>> + On some machs (i.e. Zynq) the initial prescaler value thus poses
>>>> + bounds about how much the parent clock is allowed to decrease or
>>>> + increase wrt the initial clock value.
>>>> + This affects CPU_FREQ max delta from the initial frequency.
>>>> +
>>>> config ARM_TIMER_SP804
>>>> bool "Support for Dual Timer SP804 module" if COMPILE_TEST
>>>> depends on GENERIC_SCHED_CLOCK && CLKDEV_LOOKUP
>>>> diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
>>>> index 88b2d38a7a61..60a8047fd32e 100644
>>>> --- a/drivers/clocksource/arm_global_timer.c
>>>> +++ b/drivers/clocksource/arm_global_timer.c
>>>> @@ -31,6 +31,10 @@
>>>> #define GT_CONTROL_COMP_ENABLE BIT(1) /* banked */
>>>> #define GT_CONTROL_IRQ_ENABLE BIT(2) /* banked */
>>>> #define GT_CONTROL_AUTO_INC BIT(3) /* banked */
>>>> +#define GT_CONTROL_PRESCALER_SHIFT 8
>>>> +#define GT_CONTROL_PRESCALER_MAX 0xF
>>>> +#define GT_CONTROL_PRESCALER_MASK (GT_CONTROL_PRESCALER_MAX << \
>>>> + GT_CONTROL_PRESCALER_SHIFT)
>>>>
>>>> #define GT_INT_STATUS 0x0c
>>>> #define GT_INT_STATUS_EVENT_FLAG BIT(0)
>>>> @@ -39,6 +43,7 @@
>>>> #define GT_COMP1 0x14
>>>> #define GT_AUTO_INC 0x18
>>>>
>>>> +#define MAX_F_ERR 50
>>>> /*
>>>> * We are expecting to be clocked by the ARM peripheral clock.
>>>> *
>>>> @@ -46,7 +51,8 @@
>>>> * the units for all operations.
>>>> */
>>>> static void __iomem *gt_base;
>>>> -static unsigned long gt_clk_rate;
>>>> +struct notifier_block gt_clk_rate_change_nb;
>>>> +static u32 gt_psv_new, gt_psv_bck, gt_target_rate;
>>>> static int gt_ppi;
>>>> static struct clock_event_device __percpu *gt_evt;
>>>>
>>>> @@ -96,7 +102,10 @@ static void gt_compare_set(unsigned long delta, int periodic)
>>>> unsigned long ctrl;
>>>>
>>>> counter += delta;
>>>> - ctrl = GT_CONTROL_TIMER_ENABLE;
>>>> + ctrl = readl(gt_base + GT_CONTROL);
>>>> + ctrl &= ~(GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE |
>>>> + GT_CONTROL_AUTO_INC | GT_CONTROL_AUTO_INC);
>>>> + ctrl |= GT_CONTROL_TIMER_ENABLE;
>>>> writel_relaxed(ctrl, gt_base + GT_CONTROL);
>>>> writel_relaxed(lower_32_bits(counter), gt_base + GT_COMP0);
>>>> writel_relaxed(upper_32_bits(counter), gt_base + GT_COMP1);
>>>> @@ -123,7 +132,7 @@ static int gt_clockevent_shutdown(struct clock_event_device *evt)
>>>>
>>>> static int gt_clockevent_set_periodic(struct clock_event_device *evt)
>>>> {
>>>> - gt_compare_set(DIV_ROUND_CLOSEST(gt_clk_rate, HZ), 1);
>>>> + gt_compare_set(DIV_ROUND_CLOSEST(gt_target_rate, HZ), 1);
>>>> return 0;
>>>> }
>>>>
>>>> @@ -177,7 +186,7 @@ static int gt_starting_cpu(unsigned int cpu)
>>>> clk->cpumask = cpumask_of(cpu);
>>>> clk->rating = 300;
>>>> clk->irq = gt_ppi;
>>>> - clockevents_config_and_register(clk, gt_clk_rate,
>>>> + clockevents_config_and_register(clk, gt_target_rate,
>>>> 1, 0xffffffff);
>>>> enable_percpu_irq(clk->irq, IRQ_TYPE_NONE);
>>>> return 0;
>>>> @@ -232,9 +241,28 @@ static struct delay_timer gt_delay_timer = {
>>>> .read_current_timer = gt_read_long,
>>>> };
>>>>
>>>> +static void gt_write_presc(u32 psv)
>>>> +{
>>>> + u32 reg;
>>>> +
>>>> + reg = readl(gt_base + GT_CONTROL);
>>>> + reg &= ~GT_CONTROL_PRESCALER_MASK;
>>>> + reg |= psv << GT_CONTROL_PRESCALER_SHIFT;
>>>> + writel(reg, gt_base + GT_CONTROL);
>>>> +}
>>>> +
>>>> +static u32 gt_read_presc(void)
>>>> +{
>>>> + u32 reg;
>>>> +
>>>> + reg = readl(gt_base + GT_CONTROL);
>>>> + reg &= GT_CONTROL_PRESCALER_MASK;
>>>> + return reg >> GT_CONTROL_PRESCALER_SHIFT;
>>>> +}
>>>> +
>>>> static void __init gt_delay_timer_init(void)
>>>> {
>>>> - gt_delay_timer.freq = gt_clk_rate;
>>>> + gt_delay_timer.freq = gt_target_rate;
>>>> register_current_timer_delay(&gt_delay_timer);
>>>> }
>>>>
>>>> @@ -243,18 +271,81 @@ static int __init gt_clocksource_init(void)
>>>> writel(0, gt_base + GT_CONTROL);
>>>> writel(0, gt_base + GT_COUNTER0);
>>>> writel(0, gt_base + GT_COUNTER1);
>>>> - /* enables timer on all the cores */
>>>> - writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
>>>> + /* set prescaler and enable timer on all the cores */
>>>> + writel(((CONFIG_ARM_GT_INITIAL_PRESCALER_VAL - 1) <<
>>>> + GT_CONTROL_PRESCALER_SHIFT)
>>>> + | GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
>>>>
>>>> #ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
>>>> - sched_clock_register(gt_sched_clock_read, 64, gt_clk_rate);
>>>> + sched_clock_register(gt_sched_clock_read, 64, gt_target_rate);
>>>> #endif
>>>> - return clocksource_register_hz(&gt_clocksource, gt_clk_rate);
>>>> + return clocksource_register_hz(&gt_clocksource, gt_target_rate);
>>>> +}
>>>> +
>>>> +static int gt_clk_rate_change_cb(struct notifier_block *nb,
>>>> + unsigned long event, void *data)
>>>> +{
>>>> + struct clk_notifier_data *ndata = data;
>>>> +
>>>> + switch (event) {
>>>> + case PRE_RATE_CHANGE:
>>>> + {
>>>> + int psv;
>>>> +
>>>
>>>> + psv = DIV_ROUND_CLOSEST(ndata->new_rate,
>>>> + gt_target_rate);
>>>> +
>>>
>>>> + if (abs(gt_target_rate - (ndata->new_rate / psv)) > MAX_F_ERR)
>>>> + return NOTIFY_BAD;
>>>
>>> This psv variable can become a 0 divider.
>>>
>>>> +
>>>> + psv--;
>>>> +
>>>> + /* prescaler within legal range? */
>>>> + if (psv < 0 || psv > GT_CONTROL_PRESCALER_MAX)
>>>> + return NOTIFY_BAD;
>>>> +
>>>> + /*
>>>> + * store timer clock ctrl register so we can restore it in case
>>>> + * of an abort.
>>>> + */
>>>> + gt_psv_bck = gt_read_presc();
>>>> + gt_psv_new = psv;
>>>> + /* scale down: adjust divider in post-change notification */
>>>> + if (ndata->new_rate < ndata->old_rate)
>>>> + return NOTIFY_DONE;
>>>> +
>>>> + /* scale up: adjust divider now - before frequency change */
>>>> + gt_write_presc(psv);
>>>> + break;
>>>> + }
>>>> + case POST_RATE_CHANGE:
>>>> + /* scale up: pre-change notification did the adjustment */
>>>> + if (ndata->new_rate > ndata->old_rate)
>>>> + return NOTIFY_OK;
>>>> +
>>>> + /* scale down: adjust divider now - after frequency change */
>>>> + gt_write_presc(gt_psv_new);
>>>> + break;
>>>> +
>>>> + case ABORT_RATE_CHANGE:
>>>> + /* we have to undo the adjustment in case we scale up */
>>>> + if (ndata->new_rate < ndata->old_rate)
>>>> + return NOTIFY_OK;
>>>> +
>>>> + /* restore original register value */
>>>> + gt_write_presc(gt_psv_bck);
>>>> + break;
>>>> + default:
>>>> + return NOTIFY_DONE;
>>>> + }
>>>> +
>>>> + return NOTIFY_DONE;
>>>> }
>>>>
>>>> static int __init global_timer_of_register(struct device_node *np)
>>>> {
>>>> struct clk *gt_clk;
>>>> + static unsigned long gt_clk_rate;
>>>> int err = 0;
>>>>
>>>> /*
>>>> @@ -292,11 +383,20 @@ static int __init global_timer_of_register(struct device_node *np)
>>>> }
>>>>
>>>> gt_clk_rate = clk_get_rate(gt_clk);
>>>> + gt_target_rate = gt_clk_rate / CONFIG_ARM_GT_INITIAL_PRESCALER_VAL;
>>>> + gt_clk_rate_change_nb.notifier_call =
>>>> + gt_clk_rate_change_cb;
>>>> + err = clk_notifier_register(gt_clk, &gt_clk_rate_change_nb);
>>>> + if (err) {
>>>> + pr_warn("Unable to register clock notifier\n");
>>>> + goto out_clk;
>>>> + }
>>>> +
>>>> gt_evt = alloc_percpu(struct clock_event_device);
>>>> if (!gt_evt) {
>>>> pr_warn("global-timer: can't allocate memory\n");
>>>> err = -ENOMEM;
>>>> - goto out_clk;
>>>> + goto out_clk_nb;
>>>> }
>>>>
>>>> err = request_percpu_irq(gt_ppi, gt_clockevent_interrupt,
>>>> @@ -326,6 +426,8 @@ static int __init global_timer_of_register(struct device_node *np)
>>>> free_percpu_irq(gt_ppi, gt_evt);
>>>> out_free:
>>>> free_percpu(gt_evt);
>>>> +out_clk_nb:
>>>> + clk_notifier_unregister(gt_clk, &gt_clk_rate_change_nb);
>>>> out_clk:
>>>> clk_disable_unprepare(gt_clk);
>>>> out_unmap: