Re: [PATCH v22 02/11] clocksource: arm_arch_timer: separate out device-tree code and remove arch_timer_detect_rate

From: Fu Wei
Date: Wed Mar 29 2017 - 11:02:01 EST

On 29 March 2017 at 22:41, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> wrote:
> On Wed, Mar 29, 2017 at 01:11:58PM +0800, Fu Wei wrote:
>> Hi Daniel,
>>
>> On 29 March 2017 at 11:41, Fu Wei <fu.wei@xxxxxxxxxx> wrote:
>> > Hi Daniel,
>> >
>> > Great thanks for your review, allow me to answer your question below:
>> >
>> > On 28 March 2017 at 22:58, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> wrote:
>> >> On Wed, Mar 22, 2017 at 12:31:13AM +0800, fu.wei@xxxxxxxxxx wrote:
>> >>> From: Fu Wei <fu.wei@xxxxxxxxxx>
>> >>>
>> >>> Currently, the counter frequency detection call(arch_timer_detect_rate)
>> >>> includes getting the frequency from the device-tree property, the per-cpu
>> >>> arch-timer and the memory-mapped (MMIO) timer interfaces.
>> >>> But reading device-tree property will be needed only when system boot with
>> >>> device-tree, and reading from the per-cpu arch-timer and the memory-mapped
>> >>> (MMIO) timer interfaces will be needed only when the system initializes
>> >>> the relevant timer.
>> >>>
>> >>> This patch separates out device-tree code, keep them in device-tree init
>> >>> function, and removes arch_timer_detect_rate founction, then uses the
>> >>> arch_timer_get_cntfrq and arch_timer_mem_get_cntfrq directly.
>> >>>
>> >>> Signed-off-by: Fu Wei <fu.wei@xxxxxxxxxx>
>> >>> ---
>> >>> drivers/clocksource/arm_arch_timer.c | 58 +++++++++++++++++++-----------------
>> >>> 1 file changed, 30 insertions(+), 28 deletions(-)
>> >>>
>> >>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>> >>> index 843f923..29ca7d6 100644
>> >>> --- a/drivers/clocksource/arm_arch_timer.c
>> >>> +++ b/drivers/clocksource/arm_arch_timer.c
>> >>> @@ -560,30 +560,6 @@ static u32 arch_timer_mem_get_cntfrq(void __iomem *cntbase)
>> >>> return readl_relaxed(cntbase + CNTFRQ);
>> >>> }
>> >>>
>> >>> -static void
>> >>> -arch_timer_detect_rate(void __iomem *cntbase, struct device_node *np)
>> >>> -{
>> >>> - /* Who has more than one independent system counter? */
>> >>> - if (arch_timer_rate)
>> >>> - return;
>> >>> -
>> >>> - /*
>> >>> - * Try to determine the frequency from the device tree or CNTFRQ,
>> >>> - * if ACPI is enabled, get the frequency from CNTFRQ ONLY.
>> >>> - */
>> >>> - if (!acpi_disabled ||
>> >>> - of_property_read_u32(np, "clock-frequency", &arch_timer_rate)) {
>> >>> - if (cntbase)
>> >>> - arch_timer_rate = arch_timer_mem_get_cntfrq(cntbase);
>> >>> - else
>> >>> - arch_timer_rate = arch_timer_get_cntfrq();
>> >>> - }
>> >>> -
>> >>> - /* Check the timer frequency. */
>> >>> - if (arch_timer_rate == 0)
>> >>> - pr_warn("frequency not available\n");
>> >>> -}
>> >>> -
>> >>> static void arch_timer_banner(unsigned type)
>> >>> {
>> >>> pr_info("%s%s%s timer(s) running at %lu.%02luMHz (%s%s%s).\n",
>> >>> @@ -958,7 +934,17 @@ static int __init arch_timer_of_init(struct device_node *np)
>> >>> for (i = ARCH_TIMER_PHYS_SECURE_PPI; i < ARCH_TIMER_MAX_TIMER_PPI; i++)
>> >>> arch_timer_ppi[i] = irq_of_parse_and_map(np, i);
>> >>>
>> >>> - arch_timer_detect_rate(NULL, np);
>> >>> + /*
>> >>> + * Try to determine the frequency from the device tree,
>> >>> + * if fail, get the frequency from the sysreg CNTFRQ.
>> >>> + */
>> >>> + if (!arch_timer_rate &&
>> >>
>> >> This variable is set only if "arm,armv7-timer" and "arm,armv7-timer-mem" are
>> >> declared together in the DT, right ?
>> >>
>> >> Two declarations for a single variable ? Ignore the !arch_timer_rate.
>> >
>> > In this function, we try to initialize per-CPU arm arch_timer by DT.
>> > this "!arch_timer_rate" is for testing that if we have got system
>> > counter frequency from the memory-mapped timer. If so, we just skip
>> > getting the frequency from DT or sysreg cntfrq again.
>> > This variable is set only if "arm,armv7-timer-mem" is initialized
>> > earlier than "arm,armv7-timer", in another word, maybe the node of
>> > "arm,armv7-timer-mem" is declared earlier than "arm,armv7-timer-mem"
>> > one in DT.
>> >
>> > we do this check is for keeping the same init logic as before in the
>> > DT, try to avoid any possibility of breaking devices which boot by
>> > DT.
>> >
>> >>
>> >>> + of_property_read_u32(np, "clock-frequency", &arch_timer_rate))
>> >>> + arch_timer_rate = arch_timer_get_cntfrq();
>> >>> + if (!arch_timer_rate) {
>> >>> + pr_err(FW_BUG "frequency not available.\n");
>> >>> + return -EINVAL;
>> >>> + }
>> >>
>> >> Please, clarify this block, the conditions are unclear.
>> >
>> > this "!arch_timer_rate" is for verifying that if the system counter
>> > frequency we just got from DT or sysreg cntfrq is valid(non-zero).
>> >
>> > So here, you can see I check arch_timer_rate twice, but they are for
>> > different cases.
>>
>> I think about this several times,
>> For this block, it is a little unclear, so I think this will be better:
>>
>> + /*
>> + * Try to determine the frequency:
>> + * If we have got it in arch_timer_mem_of_init, we don't need to get
>> it again, skip.
>> + * Otherwise, try to get the frequency from the device tree,
>> + * if fail, try to get it from the sysreg CNTFRQ.
>> + * Last, verify the arch_timer_rate before leaving this block.
>> + */
>> + if (!arch_timer_rate) {
>> + if (of_property_read_u32(np, "clock-frequency", &arch_timer_rate))
>> + arch_timer_rate = arch_timer_get_cntfrq();
>> + if (!arch_timer_rate) {
>> + pr_err(FW_BUG "frequency not available.\n");
>> + return -EINVAL;
>> + }
>> + }
>
> Hi Fu Wei,
>
> in my previous comment, I was suggesting to remove the first arch_timer_rate
> check.
>
> The code assumes something else initialized this variable. There is clearly a
> conflict in the variable assignment. So if a node is defined twice for this
> variable, then it is more sane to consider the second pass overwrites the first
> one. As the DT are specifying the same rate, for -mem and !-mem, then it should
> have not an impact (to be verified).

So the code will be like this:

+ /*
+ * Try to determine the frequency:
+ * If we try to get the frequency from the device tree,
+ * if fail, try to get it from the sysreg CNTFRQ.
+ * Then verify the arch_timer_rate.
+ */
+ if (of_property_read_u32(np, "clock-frequency", &arch_timer_rate))
+ arch_timer_rate = arch_timer_get_cntfrq();
+ if (!arch_timer_rate) {
+ pr_err(FW_BUG "frequency not available.\n");
+ return -EINVAL;
+ }

I am OK to delete the first arch_timer_rate check,
If arch_timer_mem is initialized first, we just overwrite the
existing rate to arch_timer rate.
This makes sense to me.

--
Best regards,

Fu Wei
Software Engineer
Red Hat