linux-kernel - Re: [PATCH] ASoC: fsl_spdif: don't change the root clock rate of spdif in driver

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Message-ID: <20140917022440.GA3216@Asurada>
Date:	Tue, 16 Sep 2014 19:24:40 -0700
From:	Nicolin Chen <nicoleotsuka@...il.com>
To:	Shawn Guo <shawn.guo@...escale.com>
Cc:	Shengjiu Wang <shengjiu.wang@...escale.com>, timur@...i.org,
	Li.Xiubo@...escale.com, lgirdwood@...il.com, broonie@...nel.org,
	perex@...ex.cz, tiwai@...e.de, alsa-devel@...a-project.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ASoC: fsl_spdif: don't change the root clock rate of
 spdif in driver

On Wed, Sep 17, 2014 at 09:32:52AM +0800, Shawn Guo wrote:
> On Tue, Sep 16, 2014 at 11:19:28AM -0700, Nicolin Chen wrote:
> > On Tue, Sep 16, 2014 at 07:46:34PM +0800, Shengjiu Wang wrote:
> > > The spdif root clock may be used by other module or defined with
> > > CLK_SET_RATE_GATE, so we can't change the clock rate in driver.
> > > In this patch remove the clk_set_rate and clk_round_rate to protect the
> > > clock.
> > 
> > It's a quite convenient and conservative way to remove the clock
> > dealing code in the driver, however, it may result less flexible
> > functionalities.
> > 
> > The reason why I left the clk_set_rate() in the driver is to hope
> > we may find a better way to tackle those tough situations. For IP
> > itself, it doesn't matter if the clock the SoC provides to it is
> > being shared by other modules or not.
> > 
> > So I think, if it's a shared clock, we should not define it as a
> > rate-changeable one in the SoC level, as we might still have some
> > SoCs provide a dedicated clock to S/PDIF so as to get the maximum
> > range of clock support for users.
> > 
> > @Shawn
> > Sorry to involve you in this topic. I'm not so sure if we can do
> > this in the clock driver so that the clock rate would be fixed
> > even if the driver is trying to change it. If we can, I think we
> > may use a better solution here instead.
> 
> No, we do not have anything like that today.

It's not supported in the clock API or just not implemented in our
code? Can we just register a clock without CLK_SET_RATE_PARENT to
achieve the purpose? (We are just trying to fix those PRED and PODF
dividers when the driver calls set_rate to their GATE clock.)

Thank you
Nicolin

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