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

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Date:   Fri, 2 Feb 2018 11:53:04 +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

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.

> 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).

Maxime

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

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