Date:   Tue, 23 Nov 2021 08:08:09 -0600
From:   Adam Ford <aford173@...il.com>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     Lucas Stach <l.stach@...gutronix.de>,
        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

On Mon, Nov 22, 2021 at 3:52 PM Tim Harvey <tharvey@...eworks.com> wrote:
>
> On Mon, Nov 22, 2021 at 10:20 AM Lucas Stach <l.stach@...gutronix.de> wrote:
> >
> > 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.

There are a significant number of peripherals which are defined and
marked as 'disabled' by default, so I don't think it's unreasonable to
do that here.
I'd like to propose we keep the default disabled and people who
need/want the GPU enabled can turn it on.  Why waste the power if it's
not needed?

> >
> > > 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.
> >
>
> Lucas,
>
> I agree - the boot firmware is an appropriate place for this. I
> believe the correct course of action in the case of the IMX8M Nano
> would be to do the following for no GPU:
> - disable disp_blk_ctrl node

I don't think it's necessary to remove the disp_blk_ctrl node or
change it.  The GPU doesn't directly interact with it.  LCD, CSI, and
DSI do, but I don't think they are removed.  The gpu only interacts
with the pgc_gpumix and neither the gpu nor gpumix currently interact
with the disp_blk_ctrl.

adam



> - disable gpu node
> - disable pgc_gpumix node
>
> What would you propose to do for detection of this in boot firmware?
> The DIGPROG register is currently used in U-Boot to determine IMX8M
> variants including Nano
> Qad/Dual/Solo/QaudLite/DualLite/SoloLite/UltraLite Quad/UltraLite
> Dual/UltraLite Solo. It would appear all the 'Lite' and 'UltraLite'
> variants have no GPU.
>
> Best regards,
>
> Tim

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