linux-kernel - Re: [PATCH v2 6/9] clk: at91: clk-generated: make gclk determine audio

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Date:   Thu, 6 Jul 2017 18:08:31 +0200
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Nicolas Ferre <nicolas.ferre@...rochip.com>
Cc:     Quentin Schulz <quentin.schulz@...e-electrons.com>,
        mturquette@...libre.com, sboyd@...eaurora.org, robh+dt@...nel.org,
        mark.rutland@....com, lgirdwood@...il.com, broonie@...nel.org,
        linux@...linux.org.uk, boris.brezillon@...e-electrons.com,
        perex@...ex.cz, tiwai@...e.com, cyrille.pitchen@...ev4u.fr,
        thomas.petazzoni@...e-electrons.com, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        alsa-devel@...a-project.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 6/9] clk: at91: clk-generated: make gclk determine
 audio_pll rate

On 06/07/2017 at 17:29:22 +0200, Nicolas Ferre wrote:
> > +	/*
> > +	 * The audio_pll rate can be modified, unlike the five others clocks
> > +	 * that should never be altered.
> > +	 * The audio_pll can technically be used by multiple consumers. However,
> > +	 * with the rate locking, the first consumer to enable to clock will be
> > +	 * the one definitely setting the rate of the clock.
> > +	 * Since audio IPs are most likely to request the same rate, we enforce
> > +	 * that the only clks able to modify gck rate are those of audio IPs.
> > +	 */
> > +
> > +	if (gck->id != GCK_ID_SSC0 && gck->id != GCK_ID_SSC1 &&
> > +	    gck->id != GCK_ID_I2S0 && gck->id != GCK_ID_I2S1 &&
> > +	    gck->id != GCK_ID_CLASSD)
> > +		goto end;
> 
> ...well... maybe for a temporary solution, but what about the next
> product that will also have such feature but without the same set of IDs?
> 

It will have a different compatible and that can be used to encode the
difference.

> I know that the main use of this clock is the "audio" subsystem (so its
> name) but in a machine without audio needs, it can be interesting to use
> this fractional PLL for other devices that can handle a GCK (and I'm
> thinking about the SDHCI interface that then could be configured with
> maximum clock speed).
> 
> > +	parent = clk_hw_get_parent_by_index(hw, GCK_INDEX_DT_AUDIO_PLL);
> > +	if (!parent)
> > +		goto end;
> 
> Here, if the audio pll id changes in the DT, we don't retrieve the
> proper parent... And again, not very future proof.
> 

One more reason to remove all the crap we have in the DT, as suggested
by RobH.


-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com