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From: Mark Brown <broonie@kernel.org>
To: Richard Fitzgerald <rf@opensource.cirrus.com>
Cc: alsa-devel@alsa-project.org, patches@opensource.cirrus.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 04/12] ASoC: cs42l42: Don't reconfigure the PLL while it is running
Date: Wed, 11 Aug 2021 15:41:43 +0100	[thread overview]
Message-ID: <20210811144143.GE4167@sirena.org.uk> (raw)
In-Reply-To: <bae1afcb-d983-c17c-d932-3afac16df501@opensource.cirrus.com>

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On Wed, Aug 11, 2021 at 01:21:24PM +0100, Richard Fitzgerald wrote:
> On 11/08/2021 12:56, Mark Brown wrote:
> > On Tue, Aug 10, 2021 at 05:27:45PM +0100, Richard Fitzgerald wrote:

> > > cs42l42_pll_config() could check whether it is already running and skip
> > > configuration in that case, but that seems to me a rather opaque
> > > implementation. In my opinion this doesn't really fall into the case of
> > > ignoring-bad-stuff-to-be-helpful (like free() accepting a NULL).

> > This doesn't treat the situation as an error though, it just ignores it,
> > and there's nothing to stop _pll_config() generating a warning if that
> > makes sense.

> It isn't an error. hw_params() will be called for both substreams
> (PLAYBACK and CAPTURE) and if one is already running we mustn't
> reconfigure the things we already configured. The DAI is marked
> symmetric so both substreams will always produce the same I2C BCLK.

If it's a noop reconfiguration then there's a case for saying that
_pll_config() should just silently do nothing anyway regardless of
issues with reconfiguring, though you might also want to warn dpeending
on other expectations.  If it's not a noop reconfiguration then
presumably the new configuration not taking effect might mean that other
things aren't going to see the clocks they expect.  Either way if a
reconfiguration gets introduced via a path other than hw_params(),
either now or later, having the check in the _pll_config() would catch
it.

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  reply	other threads:[~2021-08-11 14:42 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-10 15:37 [PATCH 00/12] ASoC: cs42l42: Series of bugfixes and improvements Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 01/12] ASoC: cs42l42: Use PLL for SCLK > 12.188MHz Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 02/12] ASoC: cs42l42: Don't claim to support 192k Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 03/12] ASoC: cs42l42: Always configure both ASP TX channels Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 04/12] ASoC: cs42l42: Don't reconfigure the PLL while it is running Richard Fitzgerald
2021-08-10 15:49   ` Mark Brown
2021-08-10 16:27     ` Richard Fitzgerald
2021-08-11 11:56       ` Mark Brown
2021-08-11 12:21         ` Richard Fitzgerald
2021-08-11 14:41           ` Mark Brown [this message]
2021-08-11 10:56     ` Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 05/12] ASoC: cs42l42: Set correct SRC MCLK Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 06/12] ASoC: cs42l42: Mark OSC_SWITCH_STATUS register volatile Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 07/12] ASoC: cs42l42: Allow time for HP/ADC to power-up after enable Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 08/12] ASoC: cs42l42: Prevent NULL pointer deref in interrupt handler Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 09/12] ASoC: cs42l42: Remove runtime_suspend/runtime_resume callbacks Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 10/12] ASoC: cs42l42: Remove redundant pll_divout member Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 11/12] ASoC: cs42l42: Add HP Volume Scale control Richard Fitzgerald
2021-08-10 15:37 ` [PATCH 12/12] ASoC: cs42l42: Add control for audio slow-start switch Richard Fitzgerald

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