From: Nikita Travkin <nikita@trvn.ru>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: thierry.reding@gmail.com, lee.jones@linaro.org,
robh+dt@kernel.org, sboyd@kernel.org, krzk@kernel.org,
linus.walleij@linaro.org, masneyb@onstation.org,
sean.anderson@seco.com, linux-pwm@vger.kernel.org,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
~postmarketos/upstreaming@lists.sr.ht
Subject: Re: [PATCH v5 2/2] pwm: Add clock based PWM output driver
Date: Sat, 19 Feb 2022 18:54:40 +0500 [thread overview]
Message-ID: <086f021bd11b7a730445250db2af01e8@trvn.ru> (raw)
In-Reply-To: <20220219101049.erwzy5mpmsfgcwjy@pengutronix.de>
Uwe Kleine-König писал(а) 19.02.2022 15:10:
> Hello,
>
> On Sat, Feb 19, 2022 at 11:46:31AM +0500, Nikita Travkin wrote:
>> Uwe Kleine-König писал(а) 14.02.2022 23:43:
>> > On Sat, Feb 12, 2022 at 09:23:42PM +0500, Nikita Travkin wrote:
>> >> + * Limitations:
>> >> + * - Glitches are possible when new pwm state is applied.
>> >> + * - Due to the fact that exact behavior depends on the underlying
>> >> + * clock driver, various limitations are possible.
>> >> + * - Period depends on the clock and, in general, not guaranteed.
>> >
>> > This sentence is broken.
>> >
>>
>> Here what I mean is that the clock driver might e.g. have a lookup table
>> for some rates and will only set one close to the requested ones.
>> (Extreme scenario is that only one rate is allowed in the lookup table,
>> which is a real possibility for some platforms that I think this driver
>> will be used with, the lookup may need to be changed for those clocks)
>>
>> I will reword this like:
>>
>> Some clock drivers may only pick the closest available rate
>> and not the exact requested one. Because of this, exact period
>> is not guaranteed.
>
> That there is no exact match is quite normal also for dedicated PWM
> HW blocks. So I think the second item in your list is good enough to
> cover the non-existing guaranteed for period and glitches.
>
Oh, I will just drop the 1 (glitches) and 3 (period) then.
Thanks for explaining!
Nikita
> Best regards
> Uwe
prev parent reply other threads:[~2022-02-19 13:54 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-12 16:23 [PATCH v5 0/2] Clock based PWM output driver Nikita Travkin
2022-02-12 16:23 ` [PATCH v5 1/2] dt-bindings: pwm: Document clk based PWM controller Nikita Travkin
2022-02-14 7:43 ` Krzysztof Kozlowski
2022-02-12 16:23 ` [PATCH v5 2/2] pwm: Add clock based PWM output driver Nikita Travkin
2022-02-14 11:19 ` Krzysztof Kozlowski
2022-02-19 6:48 ` Nikita Travkin
2022-02-14 18:43 ` Uwe Kleine-König
2022-02-19 6:46 ` Nikita Travkin
2022-02-19 10:10 ` Uwe Kleine-König
2022-02-19 13:54 ` Nikita Travkin [this message]
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