linux-kernel - Re: [PATCH 3/5] arm64: dts: allwinner: a64: add simplefb for A64 SoC

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Date:   Wed, 14 Mar 2018 09:01:08 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Harald Geyer <harald@...ib.org>
Cc:     Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andre Przywara <andre.przywara@....com>,
        Icenowy Zheng <icenowy@...c.io>, info@...mex.com
Subject: Re: [PATCH 3/5] arm64: dts: allwinner: a64: add simplefb for A64 SoC

On Tue, Mar 13, 2018 at 05:51:29PM +0100, Harald Geyer wrote:
> Maxime Ripard writes:
> > Hi,
> > 
> > On Tue, Mar 13, 2018 at 10:18:22AM +0100, Harald Geyer wrote:
> >> Maxime Ripard writes:
> >>> On Mon, Mar 12, 2018 at 04:10:48PM +0000, Harald Geyer wrote:
> >>>> The A64 SoC features two display pipelines, one has a LCD output, the
> >>>> other has a HDMI output.
> >>>>
> >>>> Add support for simplefb for the LCD output. Tested on Teres I.
> >>>>
> >>>> This patch was inspired by work of Icenowy Zheng.
> >>>>
> >>>> Signed-off-by: Harald Geyer <harald@...ib.org>
> >>>> ---
> >>>> arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 20 ++++++++++++++++++++
> >>>> 1 file changed, 20 insertions(+)
> >>>>
> >>>> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> >>> b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> >>>> index ca1b365bc722..05d5e8def68a 100644
> >>>> --- a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> >>>> +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> >>>> @@ -52,6 +52,26 @@
> >>>> 	#address-cells = <1>;
> >>>> 	#size-cells = <1>;
> >>>>
> >>>> +	chosen {
> >>>> +		#address-cells = <1>;
> >>>> +		#size-cells = <1>;
> >>>> +		ranges;
> >>>> +
> >>>> +/*
> >>>> + * The pipeline mixer0-lcd0 depends on clock CLK_MIXER0 from DE2 CCU.
> >>>> + * However there is no support for this clock on A64 yet, so we depend
> >>>> + * on the upstream clocks here to keep them (and thus CLK_MIXER0) up.
> >>>> + */
> >>> 
> >>> There's definitely support for the CLK_MIXER0 clock in the DE2 CCU
> >>> driver, so I guess this would need to be amended / fixed
> >> 
> >> AFAIK on the A64 a special sram quirk is necessary, that never got merged:
> >> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1574303.html
> >> 
> >> I asked Icenowy if I should resubmit her patch as part of this series,
> >> but was told further discussion is necessary. I'm sure she can better
> >> explain the details than me.
> >> 
> >> Actually if it wasn't for the sram quirk, there is a simplefb patch by
> >> her, that could have been merged long ago:
> >> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1574304.html
> > 
> > The issue with your patch is that, as soon as that clock is
> > functional, the DT with the node you were introducing here will no
> > longer be.
> > 
> > And since people use their firmware DT or put them in NOR these days,
> > you can't really expect them to update them every release either.
> 
> How is this a problem? - The clock can't be functional without adding
> a DT node for it's driver. So the breakage can only happen on DT update,
> which means we can avoid it, by moving the clocks to the proper places
> when we add the node actually using them for real.

Ah, sorry I missed it. Yeah, that would work.

> > I guess a proper solution would be to respin that patch.
> 
> Sure, but as mentioned above I offered to do that and was told not to.
> 
> As a compromise I could also move the simple framebuffer node from the
> A64 dtsi to the teres-i dts, where we know that the DT can be updated
> easily?

That's a matter of usecase, not only hardware, so this wouldn't work.

Maxime

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

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