linux-kernel - Re: [PATCH] clk: sunxi-ng: ccu-sun4i-a10: Fix mali changing dclk frequency

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Date:   Fri, 2 Feb 2018 14:35:16 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Giulio Benetti <giulio.benetti@...ronovasrl.com>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: sunxi-ng: ccu-sun4i-a10: Fix mali changing dclk
 frequency

On Fri, Feb 02, 2018 at 11:57:20AM +0100, Giulio Benetti wrote:
> Il 02/02/2018 11:53, Maxime Ripard ha scritto:
> > Hi,
> > 
> > On Thu, Feb 01, 2018 at 05:17:11PM +0100, Giulio Benetti wrote:
> > > > > > What kernel version did you use?
> > > > > 
> > > > > Latest mainline.
> > > > 
> > > > I guess this patch could fix it:
> > > > http://code.bulix.org/1kitrq-268936?raw
> > > 
> > > This should prevent from modifying parent clock. But my problem was
> > > different.
> > > 
> > > On A20, gpu_clk can have different PLL, not I've found out the way
> > > to choose right one with assigned-parent-clocks.
> > > 
> > > I have patchset ready for adding A20 mali node, but I need some more
> > > time to complete with OPP, then I will submit entire patchset.
> > > 
> > > Now it works correctly, using right pll(dedicated PLL8), setting
> > > right frequency.
> > 
> > The point is that we really don't care about which PLL is actually
> > being used, as long as the rate is correct and we don't break anything
> > else. If the GPU rate is accessible through one of the other PLL, it
> > makes even more sense to not use the GPU PLL and keep it disabled,
> > since it will result in some power savings.
> 
> Ah! I see the point now, very clever system for power saving.
> I'm going to check if it's resolutive,
> but it sounds good.
> 
> > 
> > > Btw, do I need to add a board using it, or can I add only Mali node
> > > to sun7i-a20.dtsi(plus other little patches)?
> > 
> > You can add it to the DTSI without a board using it (and actually,
> > nothing should be in the board DTS, everything in the DT for the Mali
> > applies to all boards).
> 
> Sure. So I would also add the patch you've addressed me:
> http://code.bulix.org/1kitrq-268936?raw
> as a commit. Can I submit it in patchset to complete the whole job?

I already sent that patch quite some time ago, I'll just apply it. You
can send the DT patch :)

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com

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