linux-kernel - Re: [PATCH V3 0/9] arm64: imx8mn: Enable more imx8m Nano functions

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Message-ID: <82c5da8862abaa430ee52b57e15d29a67106d61f.camel@pengutronix.de>
Date:   Mon, 22 Nov 2021 19:20:18 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Tim Harvey <tharvey@...eworks.com>, Adam Ford <aford173@...il.com>
Cc:     Fabio Estevam <festevam@...il.com>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Adam Ford-BE <aford@...conembedded.com>,
        Ariel D'Alessandro <ariel.dalessandro@...labora.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Device Tree Mailing List <devicetree@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 0/9] arm64: imx8mn: Enable more imx8m Nano functions

Am Montag, dem 22.11.2021 um 09:59 -0800 schrieb Tim Harvey:
> On Sun, Nov 21, 2021 at 7:25 AM Adam Ford <aford173@...il.com> wrote:
> > 
> > On Sun, Nov 21, 2021 at 8:34 AM Adam Ford <aford173@...il.com> wrote:
> > > 
> > > On Sun, Nov 21, 2021 at 8:21 AM Fabio Estevam <festevam@...il.com> wrote:
> > > > 
> > > > Hi Adam,
> > > > 
> > > > On Sun, Nov 21, 2021 at 11:17 AM Adam Ford <aford173@...il.com> wrote:
> > > > 
> > > > > I am using https://source.codeaurora.org/external/imx/imx-atf/log/?h=lf_v2.4
> > > > > 
> > > > > Since the driver sending SMCC commands to ATF isn't doing that, I
> > > > > assume it's safe to use the linux power-domain drivers with the ATF
> > > > > from NXP's kernel.
> > > > > 
> > > > > If you can point me to the repo you think I should be using, I'll give it a try.
> > > > 
> > > > Do you know if the mainline TF-A repo v2.5 works too?
> > > > https://github.com/ARM-software/arm-trusted-firmware/tree/v2.5
> > > 
> > > That's good to know.
> > > 
> > > I just built it into U-Boot:
> > > 
> > > NOTICE:  BL31: v2.5(release):v2.5
> > > NOTICE:  BL31: Built : 08:24:13, Nov 21 2021
> > > 
> > > The Etnaviv driver is still loading without hanging
> > > 
> > > root@...con-imx8mn-kit:~# dmesg |grep -i etna
> > > [   12.393936] etnaviv etnaviv: bound 38000000.gpu (ops gpu_ops [etnaviv])
> > > [   12.400676] etnaviv-gpu 38000000.gpu: model: GC7000, revision: 6203
> > > [   12.641297] [drm] Initialized etnaviv 1.3.0 20151214 for etnaviv on minor 0
> > > 
> > > 
> > 
> > Tim,
> > 
> > Which version of Nano do you have?  Not all Nano SoC's have a GPU from
> > looking at the datasheet [1] .  I am using MIMX8MN2CVTIZAA (Nano Solo)
> > 
> > [1] - https://www.nxp.com/docs/en/data-sheet/IMX8MNIEC.pdf
> > 
> 
> Adam,
> 
> The board I have here has MIMX8MN5CVTIZAA so i.MX 8M Nano QuadLite
> with 'No GPU' as you expected.
> 
> So I have to add the following to keep my board from hanging after your series:
> diff --git a/arch/arm64/boot/dts/freescale/imx8mn-venice-gw7902.dts
> b/arch/arm64/boot/dts/freescale/imx8mn-venice-gw7902.dts
> index 236f425e1570..0d256a607b7c 100644
> --- a/arch/arm64/boot/dts/freescale/imx8mn-venice-gw7902.dts
> +++ b/arch/arm64/boot/dts/freescale/imx8mn-venice-gw7902.dts
> @@ -251,6 +251,10 @@
>         };
>  };
> 
> +&gpu {
> +       status = "disabled";
> +};
> +
>  &i2c1 {
>         clock-frequency = <100000>;
>         pinctrl-names = "default";
> 
> This situation is similar to the one I encountered with the
> imx8mm-venice-gw7901 where adding the GPC node caused my board (which
> did not power the GPU) to hang until I added disables to the
> device-tree with commit 7973009235e2 ("arm64: dts:
> imx8mm-venice-gw7901.dts: disable pgc_gpumix"). It feels painful to
> have to add patches to keep things from hanging after additional
> functionality is added to dt but perhaps that is more common than I
> think esp for SoC's like IMX8M which have a lot of lingering support
> still coming in.
> 
Yea, it's unfortunate that those patches break your board, but I guess
we need to accept this, while there is still a lot of feature work
going on.

> I don't mind at all submitting the above patch to fix my board after
> your series is accepted as I think that having an IMX8MN with 'no gpu'
> is perhaps less likely than having one with a GPU and thus we probably
> shouldn't mark the node as disabled and force everyone that has a GPU
> to go and enable it.
> 
> I wonder however if we should think about adding something to etnaviv
> to check the capability so that the same dt could be used with both
> CPU variants?

etnaviv or really the kernel at all is not the place to handle this.
The DT is supposed to describe the hardware and the kernel should be
able to trust this description.

If there is some way to read the chip capabilities and avoid having too
much DT variants in the kernel, the right place to handle this is the
software running before the kernel is started, i.e. your bootloader.
Barebox for example reads the SCU fuses on i.MX6 and removes the DT
nodes for the fused off CPU cores on i.MX6S and i.MX6D.

Regards,
Lucas