Re: [PATCH 06/13] iio: adc: rockchip_saradc: Benefit from devm_clk_get_enabled() to simplify

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

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On Mon, Aug 15, 2022 at 10:30:45AM +0300, Andy Shevchenko wrote:
> On Mon, Aug 15, 2022 at 12:31 AM Uwe Kleine-König
> <u.kleine-koenig@pengutronix.de> wrote:
> >
> > Hello,
> >
> > [dropped Tomislav Denis from Cc: as the address bounces]
> >
> > On Sun, Aug 14, 2022 at 10:01:08PM +0300, Andy Shevchenko wrote:
> > > On Sat, Aug 13, 2022 at 7:21 PM Jonathan Cameron <jic23@kernel.org> wrote:
> > > >
> > > > On Mon,  8 Aug 2022 22:47:33 +0200
> > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > >
> > > > > Make use of devm_clk_get_enabled() to replace some code that effectively
> > > > > open codes this new function.
> > > > >
> > > > > Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> > > > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > > >
> > > > This might have side effects as it now enables the clock before calling
> > > > the clk_set_rate(). Also changes the clock start up ordering. Neither is that
> > > > scary a change, but on really fussy hardware they might cause problems.
> > > >
> > > > Add a few rock-chips people who have sent patches in last few years
> > > > to hopefully take a look or even better run a test.
> > >
> > > I believe you found a bug in the patch. The possible solutions are:
> > > - not take the patch
> > > - disable and re-enable clock around clk_set_rate()
> > >
> > > IIRC clk_set_rate() will spit a WARN if clock is enabled.
> >
> > You mean in general? I think that's wrong. There might be some clks that
> > do that, but I'd consider them strange. If you ask me, calling
> > clk_set_rate() for a *disabled* clk is the strange concept ...
> 
> I think it's correct from the logic and electrical perspective. That's
> why the preparation and enablement are separated in CCF. But please
> double check, because I can't remember everything by heart.

In my book the separation is done because "enabling" has to sleep for
some clks (e.g. PLLs) while a sleeping clk_enable() is bad for various
use cases and most clks don't sleep for enabling.

Anyhow, I don't have the hardware, so I'd rely on someone who can
actually test that.

Best regards
Uwe

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

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