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

[Daniel Lezcano]

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).