linux-kernel - Re: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal to system freq

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Message-ID: <20170907230345.GA20531@Asurada-Nvidia>
Date:   Thu, 7 Sep 2017 16:03:48 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Łukasz Majewski <lukma@...x.de>,
        Timur Tabi <timur@...i.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal
 to system freq

On Thu, Sep 07, 2017 at 02:44:11PM +0100, Mark Brown wrote:
 
> > On the other hand, the sys clock (baudclk in the driver) should be
> > configured whenever it's related to external clock outputs. When I
> > implemented this set_sysclk() for fsl_ssi.c, I used it to set this
> > sys clock (baudclk) by a machine driver, in order to set bit clock.
> > Then someone patched the driver by moving all the code to set_bclk()
> > to make machine drivers simpler. Now the set_sysclk() is remained
> > to give machine drivers a chance to override clock configurations
> > in the hw_params(). This could be used in TDM or some other special
> > cases (It could also have a purpose for backwards compatibility).
> 
> > So here, we should set baudclk (BCLK generator).
> 
> No, that's just going to cause confusion - if all the other drivers are
> using set_sysclk() to set an input clock rate to the IP rather than an
> output clock but your driver does something else then sooner or later
> someone will run into trouble with that.  

I admit I had that concern. Probably I should have deprecated this
set_sysclk(). I will try to patch it and hw_params() accordingly.