linux-kernel - Re: [RFC PATCH v1] Revert "pwm: Clear chip_data in pwm

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Message-ID: <20230308165202.gaeziqdncbkeo5l6@pengutronix.de>
Date:   Wed, 8 Mar 2023 17:52:02 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     George Stark <GNStark@...rdevices.ru>
Cc:     "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "krzysztof.kozlowski@...aro.org" <krzysztof.kozlowski@...aro.org>,
        "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>, kernel <kernel@...rdevices.ru>
Subject: Re: [RFC PATCH v1] Revert "pwm: Clear chip_data in pwm_put()"

Hello George,

On Wed, Mar 08, 2023 at 12:16:00PM +0000, George Stark wrote:
> On 3/8/23 00:28, Uwe Kleine-König wrote:
> > If you ask me, better drop pwm_set_chip_data() completely. It adds no
> > useful value. It's just a variant of driver data and using both
> > complicates the driver and probably fragments memory allocations. Also
> > the sematic of driver data is better known as it's the same for all
> > subsystems.
> >
> > Do you use the capture functionality? In my eyes the capture part of the
> > pwm subsystem is very alien. Only a small subset of the hardware
> > supports this and the counter framework should be better suited for such
> > tasks.
> I don't use pwm-sti driver. I update meson pwm driver for new chips
> and when started using pwm_set_chip_data in probe I was very surprised that
> my data is lost after sysfs export/unexport calls. Then I found the 
> patch and
> checked other drivers for similar usecases.

OK.

> Probably you're right about dropping pwm_set_chip_data.

If you want to tackle that, you might want to take

	https://lore.kernel.org/all/20210504132537.62072-2-u.kleine-koenig@pengutronix.de/

into account. (Both to reuse this patch to prepare pwm-berlin for
dropping pwm_set_chip_data and to be prepared that back then Thierry
opposed to the idea.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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