linux-kernel - Re: [PATCH] ASoC: fsl_sai: Correct the clock source for mclk0

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Message-ID: <20201119055340.GA1666@Asurada-Nvidia>
Date:   Wed, 18 Nov 2020 21:53:41 -0800
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Shengjiu Wang <shengjiu.wang@...il.com>
Cc:     Shengjiu Wang <shengjiu.wang@....com>, alsa-devel@...a-project.org,
        Timur Tabi <timur@...nel.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        linuxppc-dev@...ts.ozlabs.org, Takashi Iwai <tiwai@...e.com>,
        Mark Brown <broonie@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: fsl_sai: Correct the clock source for mclk0

On Thu, Nov 19, 2020 at 01:28:32PM +0800, Shengjiu Wang wrote:
> On Thu, Nov 19, 2020 at 1:02 PM Nicolin Chen <nicoleotsuka@...il.com> wrote:
> >
> > On Thu, Nov 19, 2020 at 10:29:16AM +0800, Shengjiu Wang wrote:
> > > On VF610, mclk0 = bus_clk;
> > > On i.MX6SX/6UL/6ULL/7D, mclk0 = mclk1;
> > > On i.MX7ULP, mclk0 = bus_clk;
> > > On i.MX8QM/8QXP, mclk0 = bus_clk;
> > > On i.MX8MQ/8MN/8MM/8MP, mclk0 = bus_clk;
> > >
> > > So add variable mclk0_mclk1_match in fsl_sai_soc_data To
> >
> > Not in favor of "mclk0_mclk1_match" as it doesn't sound explicit
> > to me. Instead, "mclk0_is_bus_clk" or "mclk0_is_mclk1" might be
> > better. Or in case that you foresee some other implementation:
> >
> > enum {
> >         MCLK0_IS_BUS_CLK,
> >         MCLK0_IS_MCLK1,
> > };
> >
> > static const struct fsl_sai_soc_data fsl_sai_vf610_data = {
> > +       .mclk0_alias = MCLK0_IS_BUS_CLK,
> > };
> 
> No problem.
> 
> But I just find this patch doesn't consider the mqs case.
> MCLK0 can't be used for mqs, it needs MCLK1, even
> the MCLK0 is same as MCLK1,  MCLK1 need to be
> selected for mqs case.
> 
> Is there a decent way for this case?

Is there any use case that we have to use MCLK0 instead of MCLK1
on SoCs where MCLK0=MCLK1? If no, how about skip MCLK0 at all in
the for-loop at fsl_sai_set_bclk?

	/*
	 * There is no point in polling MCLK0 if it is identical to MCLK1.
	 * And given that MQS use case has to use MCLK1 though two clocks
	 * are the same, we simply skip MCLK0 and start to find from MCLK1.
	 */
	id = mclk0_is_mclk1 ? 1 : 0;

	for (; id < FSL_SAI_MCLK_MAX; id++) {