linux-kernel - Re: [PATCH] arm64: dts: imx8mm: Add GPU node

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Date:   Thu, 22 Oct 2020 13:31:29 -0500
From:   Adam Ford <aford173@...il.com>
To:     Marek Vasut <marex@...x.de>
Cc:     arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Adam Ford-BE <aford@...conembedded.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: imx8mm: Add GPU node

On Thu, Oct 22, 2020 at 1:17 PM Marek Vasut <marex@...x.de> wrote:
>
> On 10/22/20 7:16 PM, Adam Ford wrote:
> > According to the documentation from NXP, the i.MX8M Nano has a
> > Vivante GC7000 Ultra Lite as its GPU core.
> >
> > With this patch, the Etnaviv driver presents the GPU as:
> >    etnaviv-gpu 38000000.gpu: model: GC7000, revision: 6203
> >
> > It uses the GPCV2 controller to enable the power domain for the GPU.
>
> Subject should say 8mn , not 8mm .

ugh.. My mistake.  I'll submit a V2 once other have had a chance to
give some feedback.

Maybe NXP can comment on the dialog below.

>
> Are the assigned-clock-rates correct ?

I used the assigned clock rates from the vendor kernel, with the
exception of running at 400MHz instead of 600MHz.  According to the
datasheet, the GPU clock needs to be 400MHZ to run at 0.85V. The
600MHz operating point for the GPU requires a 0.95V operating point.
Since the default operating point for the Nano shows 0.85V, I left the
GPU clock lower to match the normal operating speed.  This varies a
bit from the vendor kernel, but their kernel is also showing a 0.95V
operating point, so I think that's why they are specifying a 600MHz
operating point.

On the Beacon embedded board, we're driving the LPDDR to 800MHz which
requires the ARM to run at .95V.   I was able to override the
assigned-clock rates for my board to run at 600MHz, and change the ARM
operating point to .95V to meet the spec.

My intent was to use the defaults and let the board files override
them.   If you want, I can try to look through the board files to see
what operating point their using and propose updates to those
respective device trees to address the clocks on those boards.

adam