linux-kernel - Re: [PATCH v16 14/15] clocksource/drivers/arm_arch_timer: Add GTDT support for memory-mapped timer

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Date:   Wed, 23 Nov 2016 20:15:45 +0800
From:   Fu Wei <fu.wei@...aro.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        rruigrok@...eaurora.org, "Abdulhamid, Harb" <harba@...eaurora.org>,
        Christopher Covington <cov@...eaurora.org>,
        Timur Tabi <timur@...eaurora.org>,
        G Gregory <graeme.gregory@...aro.org>,
        Al Stone <al.stone@...aro.org>, Jon Masters <jcm@...hat.com>,
        Wei Huang <wei@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Leo Duran <leo.duran@....com>,
        Wim Van Sebroeck <wim@...ana.be>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-watchdog@...r.kernel.org, Tomasz Nowicki <tn@...ihalf.com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Julien Grall <julien.grall@....com>
Subject: Re: [PATCH v16 14/15] clocksource/drivers/arm_arch_timer: Add GTDT
 support for memory-mapped timer

Hi Mark,

On 19 November 2016 at 04:20, Mark Rutland <mark.rutland@....com> wrote:
> On Wed, Nov 16, 2016 at 09:49:07PM +0800, fu.wei@...aro.org wrote:
>> From: Fu Wei <fu.wei@...aro.org>
>>
>> The patch add memory-mapped timer register support by using the
>> information provided by the new GTDT driver of ACPI.
>>
>> Signed-off-by: Fu Wei <fu.wei@...aro.org>
>> ---
>>  drivers/clocksource/arm_arch_timer.c | 26 +++++++++++++++++++++++++-
>>  1 file changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>> index c494ca8..0aad60a 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -1067,7 +1067,28 @@ CLOCKSOURCE_OF_DECLARE(armv7_arch_timer_mem, "arm,armv7-timer-mem",
>>                      arch_timer_mem_of_init);
>>
>>  #ifdef CONFIG_ACPI_GTDT
>> -/* Initialize per-processor generic timer */
>> +static int __init arch_timer_mem_acpi_init(void)
>> +{
>> +     struct arch_timer_mem *timer_mem;
>> +     int ret = 0;
>> +     int i = 0;
>> +
>> +     timer_mem = kzalloc(sizeof(*timer_mem), GFP_KERNEL);
>
> Why do you need it zeroed? You don't clear it between iterations, so
> either you don't need this, or you have a bug in the loop.
>
>> +     if (!timer_mem)
>> +             return -ENOMEM;
>> +
>> +     while (!gtdt_arch_timer_mem_init(timer_mem, i)) {
>
> Huh?
>
> Why doesn't GTDT expose a function to fill in the entire arch_timer_mem
> in one go?

Yes, that is a good idea, but I need to find a way to get the number of
GT block in GTDT, then allocate a  struct arch_timer_mem array for all GT block

>
> There shouldn't be multiple instances, as far as I am aware. Am I
> mistaken?

I don't see any doc says : there is only one memory-mapped timer
in a soc.
Maybe we have more than one GT block in GTDT or
(in another word) we may have more than one memory-mapped
timer in a soc, right ??

Please correct me, If I miss something.

>
>> +             ret = arch_timer_mem_init(timer_mem);
>> +             if (ret)
>> +                     break;
>> +             i++;
>> +     }
>> +
>> +     kfree(timer_mem);
>> +     return ret;
>> +}
>
>
> Regardless, arch_timer_mem is small enough that you don't need dynamic
> allocaiton. Just put it on the stack, e.g.
>
> static int __init arch_timer_mem_acpi_init(void)
> {
>         int i = 0;
>         struct arch_timer_mem timer_mem;
>
>         while (!gtdt_arch_timer_mem_init(timer_mem, i)) {
>                 int ret = arch_timer_mem_init();
>                 if (ret)
>                         return ret;
>                 i++
>         }
>
>         return 0;
> }
>
> Thanks,
> Mark.



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat