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SubjectRe: [PATCH v4 7/8] clocksource: Add a new timer-ingenic driver


Le mer. 28 mars 2018 à 18:25, Daniel Lezcano
<daniel.lezcano@linaro.org> a écrit :
> On 28/03/2018 17:15, Paul Cercueil wrote:
>> Le 2018-03-24 07:26, Daniel Lezcano a écrit :
>>> On 18/03/2018 00:29, Paul Cercueil wrote:
>>>> This driver will use the TCU (Timer Counter Unit) present on the
>>>> Ingenic
>>>> JZ47xx SoCs to provide the kernel with a clocksource and timers.
>>>
>>> Please provide a more detailed description about the timer.
>>
>> There's a doc file for that :)
>
> Usually, when there is a new driver I ask for a description in the
> changelog for reference.
>
>>> Where is the clocksource ?
>>
>> Right, there is no clocksource, just timers.
>>
>>> I don't see the point of using channel idx and pwm checking here.
>>>
>>> There is one clockevent, why create multiple channels ? Can't you
>>> stick
>>> to the usual init routine for a timer.
>>
>> So the idea is that we use all the TCU channels that won't be used
>> for PWM
>> as timers. Hence the PWM checking. Why is this bad?
>
> It is not bad but arguable. By checking the channels used by the pwm
> in
> the code, you introduce an adherence between two subsystems even if it
> is just related to the DT parsing part.
>
> As it is not needed to have more than one timer in the time framework
> (at least with the same characteristics), the pwm channels check is
> pointless. We can assume the author of the DT file is smart enough to
> prevent conflicts and define a pwm and a timer properly instead of
> adding more code complexity.
>
> In addition, simplifying the code will allow you to use the timer-of
> code and reduce very significantly the init function.

That's what I had in my V1 and V2, my DT node for the timer-ingenic
driver
had a "timers" property (e.g. "timers = <4 5>;") to select the channels
that
should be used as timers. Then Rob told me I shouldn't do that, and
instead
detect the channels that will be used for PWM.

>>>> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
>>>> ---
>>>> drivers/clocksource/Kconfig | 8 ++
>>>> drivers/clocksource/Makefile | 1 +
>>>> drivers/clocksource/timer-ingenic.c | 278
>>>> ++++++++++++++++++++++++++++++++++++
>>>> 3 files changed, 287 insertions(+)
>>>> create mode 100644 drivers/clocksource/timer-ingenic.c
>>>>
>>>> v2: Use SPDX identifier for the license
>>>> v3: - Move documentation to its own patch
>>>> - Search the devicetree for PWM clients, and use all the TCU
>>>> channels that won't be used for PWM
>>>> v4: - Add documentation about why we search for PWM clients
>>>> - Verify that the PWM clients are for the TCU PWM driver
>>>>
>>>> diff --git a/drivers/clocksource/Kconfig
>>>> b/drivers/clocksource/Kconfig
>>>> index d2e5382821a4..481422145fb4 100644
>>>> --- a/drivers/clocksource/Kconfig
>>>> +++ b/drivers/clocksource/Kconfig
>>>> @@ -592,4 +592,12 @@ config CLKSRC_ST_LPC
>>>> Enable this option to use the Low Power controller timer
>>>> as clocksource.
>>>>
>>>> +config INGENIC_TIMER
>>>> + bool "Clocksource/timer using the TCU in Ingenic JZ SoCs"
>>>> + depends on MACH_INGENIC || COMPILE_TEST
>>>
>>> bool "Clocksource/timer using the TCU in Ingenic JZ SoCs" if
>>> COMPILE_TEST
>>>
>>> Remove the depends MACH_INGENIC.
>>
>> This driver is not useful on anything else than Ingenic SoCs, why
>> should I
>> remove MACH_INGENIC then?
>
> For COMPILE_TEST on x86.

Well that's a logical OR right here, so it will work...

>>>> + select CLKSRC_OF
>>>> + default y
>>>
>>> No default, Kconfig platform selects the timer.
>>
>> Alright.
> [ ... ]
>
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