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

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Date:   Fri, 2 Feb 2018 11:57:20 +0100
From:   Giulio Benetti <giulio.benetti@...ronovasrl.com>
To:     Maxime Ripard <maxime.ripard@...tlin.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

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?

> 
> Maxime
> 


-- 
Giulio Benetti
R&D Manager &
Advanced Research

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