linux-kernel - RE: [PATCHv2 6/6] ASoC: da7213: Add default clock handling

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Message-ID: <AM5PR1001MB09949D557742E8817545637F80450@AM5PR1001MB0994.EURPRD10.PROD.OUTLOOK.COM>
Date:   Tue, 26 Nov 2019 17:39:45 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     Mark Brown <broonie@...nel.org>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>
CC:     Sebastian Reichel <sebastian.reichel@...labora.com>,
        Support Opensource <Support.Opensource@...semi.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...labora.com" <kernel@...labora.com>
Subject: RE: [PATCHv2 6/6] ASoC: da7213: Add default clock handling

On 26 November 2019 17:09, Mark Brown wrote:

> On Tue, Nov 26, 2019 at 04:55:39PM +0000, Adam Thomson wrote:
> > On 21 November 2019 21:49, Adam Thomson wrote:
> > > On 20 November 2019 15:24, Sebastian Reichel wrote:
> 
> > > I've thought more about this and for the scenario where a machine driver
> > > controls the PLL through a DAPM widget associated with this codec (like some
> > > Intel boards do), then the PLL will be configured once here and then again
> > > when the relevant widget is called. I don't think that will matter but I will
> > > take a further look just in case this might cause some oddities.
> 
> > So I don't see any issues per say with the PLL function being called twice in
> > the example I mentioned. However it still feels a bit clunky; You either live
> > with it or you have something in the machine driver to call the codec's PLL
> > function early doors to prevent the bias_level() code of the codec controlling
> > the PLL automatically. Am wondering though if there would be some use in
> having
> > an indicator that simple-card is being used so we can avoid this? I guess we
> 
> If we're special casing simple-card we're doing it wrong - there's
> nothing stopping any other machine driver behaving in the same way.

Ok, what's being proposed here is for the codec to automatically control the PLL
rather than leaving it to the machine driver as is the case right now. In the
possible scenario where this is done using a card level widget to enable/disable
the PLL we will conflict with that using the current suggested approach for the
da7213 driver, albeit with no real consequence other than configuring the PLL
twice the first time a stream is started. It's a case of how to determine who's
in control of the PLL here; machine driver or codec?