linux-kernel - Re: [PATCH v2 2/3] pwm: bcm2835: allow pwm driver to be used in atomic context

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Message-ID: <e3e1bca1-bffa-d97a-d4af-27a10c43c064@gmail.com>
Date:   Sat, 14 Oct 2023 09:51:12 +0300
From:   Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Alexander Stein <alexander.stein@...tq-group.com>
Cc:     Sean Young <sean@...s.org>, linux-media@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Stefan Wahren <wahrenst@....net>, linux-pwm@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] pwm: bcm2835: allow pwm driver to be used in
 atomic context



On 13.10.23 г. 20:51 ч., Uwe Kleine-König wrote:
> Hello,
> 
> On Fri, Oct 13, 2023 at 01:13:50PM +0200, Alexander Stein wrote:
>> Am Freitag, 13. Oktober 2023, 13:04:48 CEST schrieb Stefan Wahren:
>>> Am 13.10.23 um 12:46 schrieb Sean Young:
>>>> clk_get_rate() may do a mutex lock. Since the clock rate cannot change on
>>>> an rpi, simply fetch it once.
>>>
>>> does it mean you checked all possible SoCs (BCM2835, BCM2836, BCM2837,
>>> BCM2711, BCM2712) for this change?
>>>
>>> Is it impossible that the real clock can never be influenced by turbo
>>> mode like SPI?
>>
>> Assuming the clock can change, which I would, then a clock notifier seems
>> appropriate. See [1] for an example.
> 
> I'm not a fan. If the clock changes, the output also changes. With a
> clock notifier you can soften the issue and reconfigure to something
> similar as the original wave form, but a glitch happens for sure.
> 

Right, but without notifier, everything rate related after the change 
will be wrong

Ivo