linux-kernel - Re: [alsa-devel] [PATCH v2 2/2] ASoC: codec: wm8960: Relax bit clock computation

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Message-ID: <20170321143117.GZ6986@localhost.localdomain>
Date:   Tue, 21 Mar 2017 14:31:17 +0000
From:   Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
To:     Daniel Baluta <daniel.baluta@...il.com>
CC:     Daniel Baluta <daniel.baluta@....com>,
        <alsa-devel@...a-project.org>, <shengjiu.wang@...escale.com>,
        <patches@...nsource.wolfsonmicro.com>,
        "Liam Girdwood" <lgirdwood@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>, <viorel.suman@....com>,
        <mihai.serban@....com>, Takashi Iwai <tiwai@...e.com>
Subject: Re: [alsa-devel] [PATCH v2 2/2] ASoC: codec: wm8960: Relax bit clock
 computation

On Tue, Mar 21, 2017 at 04:25:40PM +0200, Daniel Baluta wrote:
> On Tue, Mar 21, 2017 at 4:20 PM, Charles Keepax
> <ckeepax@...nsource.wolfsonmicro.com> wrote:
> > On Tue, Mar 21, 2017 at 04:05:15PM +0200, Daniel Baluta wrote:
> >> On Tue, Mar 21, 2017 at 2:52 PM, Charles Keepax
> >> <ckeepax@...nsource.wolfsonmicro.com> wrote:
> >> > On Tue, Mar 21, 2017 at 12:09:36PM +0200, Daniel Baluta wrote:
> >> >>       * use a marker to check if a match is found
> >> >>       * didn't removed PLL as Charles suggested because there is
> >> >>       a special PLL mode which explictly uses PLL. We could start
> >> >>       a discussion on not using PLL when deriving bitclk, but this
> >> >>       is to be done in another patch.
> >> >>
> >> >
> >> > Could you elaborate on this a little more am I not sure I follow
> >> > 100%? There is a mode which explictly requires the PLL to be used
> >> > (WM8960_SYSCLK_PLL) but in that case your wm8960_configure_sysclk
> >> > code will not be called so I don't see what is causing that to have
> >> > an effect on this patch?
> >>
> >> My doubt is, what happens if wm8960_configure_clocking is called with
> >> wm8960->clk_id = WM8960_SYSCLK_PLL and we remove the PLL
> >> as suggested.
> >
> > I wasn't suggesting removing the PLL just that if we find a
> > "relaxed match" we don't need to then check the PLL for a better
> > match, as I suspect that a slightly higher than needed bit clock
> > has less power/performance impact than firing up the PLL.
> >
> > Which removes the need to differenciate between a relaxed and
> > bang on match in wm8960_configure_sysclk and means you don't have
> > to do the caching the values across the PLL code that you do now.
> 
> Oh, I see. So we still use the PLL when no exact or relaxed match
> is found.

Yeah exactly or in the case that it is requested directly.

Thanks,
Charles