From: John Watts <contact@jookia.org>
To: きくちゃんさん <kikuchan98@gmail.com>
Cc: privatesub2@gmail.com, aou@eecs.berkeley.edu,
bigunclemax@gmail.com, conor+dt@kernel.org,
devicetree@vger.kernel.org, fusibrandon13@gmail.com,
jernej.skrabec@gmail.com, krzk+dt@kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org,
linux-riscv@lists.infradead.org, linux-sunxi@lists.linux.dev,
mkl@pengutronix.de, p.zabel@pengutronix.de, palmer@dabbelt.com,
paul.walmsley@sifive.com, robh@kernel.org, samuel@sholland.org,
ukleinek@kernel.org, wens@csie.org
Subject: Re: [PATCH v9 0/3] Add support for Allwinner PWM on D1/T113s/R329 SoCs
Date: Thu, 23 May 2024 15:54:00 +1000 [thread overview]
Message-ID: <Zk7Z-MfdF-YKWeJ6@titan> (raw)
In-Reply-To: <CAG40kxFxE_Oj+9aCzGku0a3KFHpuW8ai=gEkV9M8==5gwmjdEA@mail.gmail.com>
On Thu, May 23, 2024 at 02:30:32PM +0900, きくちゃんさん wrote:
> Hello John,
Hello,
>
> Your method is quite impressive and challenging.
>
> I think PWM is not only for LCD backlighting, but also for signal generation.
> For instance, imagine an application software that sends a stream to
> one PWM channel to synthesize sound by changing its period (plays a
> square wave).
> By your method, if the other PWM channel is used for LCD backlighting,
> it may flicker repeatedly on DIV_M changes.
> (Or simply both channels for streo sound synthesize, you may hear lots
> of pop noise)
>
> It means the setting of one channel can affect the other, which users
> may not anticipate.
Does Linux guarantee a flicker-free experience with setting up PWM
channels, or that it doesn't affect other channels?
How do other drivers handle this situation?
Maybe out-sourcing the clocking to the device tree and letting people set the
clock and common divisor in the DT would be a good idea, with the HOSC and a
common divisor of 1 by default, then error if the value can't be found.
This would work for periods from 41ns up to 687ms by default. Using APB would
give a better resolution as by default it hangs around 5ns which is nice and
divisible by 10.
>
> Best regards,
> kikuchan.
John.
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next prev parent reply other threads:[~2024-05-23 5:55 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAG40kxGMu-TSchNezkcC_A97hzPnWU3KxeL-X-hJfPhjr_COyQ@mail.gmail.com>
2024-05-23 3:04 ` [PATCH v9 0/3] Add support for Allwinner PWM on D1/T113s/R329 SoCs John Watts
2024-05-23 5:30 ` きくちゃんさん
2024-05-23 5:54 ` John Watts [this message]
2024-05-24 11:32 ` きくちゃんさん
2024-05-20 18:42 Aleksandr Shubin
2024-10-08 15:10 ` Chris Morgan
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