Message-ID: <f5eb761e9ec30927657ed02a55e3b91abede90fe.camel@imgtec.com>
Date: Thu, 7 Mar 2024 12:37:27 +0000
From: Frank Binns <Frank.Binns@...tec.com>
To: "aford173@...il.com" <aford173@...il.com>,
        Matt Coster
	<Matt.Coster@...tec.com>
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Subject: Re: [PATCH 2/6] arm64: dts: renesas: r8a774a1: Enable GPU

On Thu, 2024-03-07 at 12:26 +0000, Frank Binns wrote:
> On Tue, 2024-02-27 at 05:50 -0600, Adam Ford wrote:
> > On Tue, Feb 27, 2024 at 3:31 AM Matt Coster <Matt.Coster@...tec.com> wrote:
> > > Hi Adam,
> > > 
> > > Thanks for these patches! I'll just reply to this one patch, but my
> > > comments apply to them all.
> > > 
> > > On 27/02/2024 03:45, Adam Ford wrote:
> > > > The GPU on the RZ/G2M is a Rogue GX6250 which uses firmware
> > > > rogue_4.45.2.58_v1.fw available from Imagination.
> > > > 
> > > > When enumerated, it appears as:
> > > >   powervr fd000000.gpu: [drm] loaded firmware powervr/rogue_4.45.2.58_v1.fw
> > > >   powervr fd000000.gpu: [drm] FW version v1.0 (build 6513336 OS)
> > > 
> > > These messages are printed after verifying the firmware blob’s headers,
> > > *before* attempting to upload it to the device. Just because they appear
> > > in dmesg does *not* imply the device is functional beyond the handful of
> > > register reads in pvr_load_gpu_id().
> > > 
> > > Since Mesa does not yet have support for this GPU, there’s not a lot
> > > that can be done to actually test these bindings.
> > > 
> > > When we added upstream support for the first GPU (the AXE core in TI’s
> > > AM62), we opted to wait until userspace was sufficiently progressed to
> > > the point it could be used for testing. This thought process still
> > > applies when adding new GPUs.
> > > 
> > > Our main concern is that adding bindings for GPUs implies a level of
> > > support that cannot be tested. That in turn may make it challenging to
> > > justify UAPI changes if/when they’re needed to actually make these GPUs
> > > functional.
> > 
> > I wrongly assumed that when the firmware was ready, there was some
> > preliminary functionality, but it sounds like we need to work for
> > Series6XT support to be added to the driver.  I only used the AXE
> > compatible since it appeared to the be the only one and the existing
> > binding document stated "model/revision is fully discoverable" which I
> > interpreted to mean that the AXE compatible was sufficient.
> 
> The comment is related to there being a few models/revisions of AXE [1][2][3],
> which we can distinguish between by reading a register.
> 
> > > > Signed-off-by: Adam Ford <aford173@...il.com>
> > > > 
> > > > diff --git a/arch/arm64/boot/dts/renesas/r8a774a1.dtsi b/arch/arm64/boot/dts/renesas/r8a774a1.dtsi
> > > > index a8a44fe5e83b..8923d9624b39 100644
> > > > --- a/arch/arm64/boot/dts/renesas/r8a774a1.dtsi
> > > > +++ b/arch/arm64/boot/dts/renesas/r8a774a1.dtsi
> > > > @@ -2352,6 +2352,16 @@ gic: interrupt-controller@...10000 {
> > > >                       resets = <&cpg 408>;
> > > >               };
> > > > 
> > > > +             gpu: gpu@...00000 {
> > > > +                     compatible = "renesas,r8a774a1-gpu", "img,img-axe";
> > > 
> > > The GX6250 is *not* an AXE core - it shouldn’t be listed as compatible
> > > with one. For prior art, see [1] where we added support for the MT8173
> > > found in Elm Chromebooks R13 (also a Series6XT GPU).
> > > 
> > > > +                     reg = <0 0xfd000000 0 0x20000>;
> > > > +                     clocks = <&cpg CPG_MOD 112>;
> > > > +                     clock-names = "core";
> > > 
> > > Series6XT cores have three clocks (see [1] again). I don’t have a
> > > Renesas TRM to hand – do you know if their docs go into detail on the
> > > GPU integration?
> > > 
> > > > +                     interrupts = <GIC_SPI 119 IRQ_TYPE_LEVEL_HIGH>;
> > > > +                     power-domains = <&sysc R8A774A1_PD_3DG_B>;
> > > > +                     resets = <&cpg 112>;
> > > > +             };
> > > > +
> > > >               pciec0: pcie@...00000 {
> > > >                       compatible = "renesas,pcie-r8a774a1",
> > > >                                    "renesas,pcie-rcar-gen3";
> > > 
> > > As you probably expect by this point, I have to nack this series for
> > > now. I appreciate your effort here and I’ll be happy to help you land
> > 
> > I get that.  I wasn't sure if I should have even pushed this, but I
> > wanted to get a little traction, because I know there are people like
> > myself who want to use the 3D in the Renesas boards, but don't want to
> > use the closed-source blobs tied to EULA and NDA documents.
> > 
> > > these once Mesa gains some form of usable support to allow testing.
> > 
> > Is there a way for your group to add me to the CC list when future
> > updates are submitted?  I'd like to follow this and resubmit when it's
> > ready.
> 
> Sure, we'll keep you updated as things progress.
> 

Oh, I forgot to add, in the meantime, would you find it useful for us to create
a Series6XT branch on GitLab where we can include these patches? We can create a
corresponding Mesa branch that we'll update as we progress support for GX6250.
This should make it easier for you (and others) to test and hopefully make it
easier for others to contribute while we work to get support into a good state.

> Thanks
> Frank
> 
> [1] https://www.imaginationtech.com/product/img-axe-1-16m/
> [2] https://www.imaginationtech.com/product/img-axe-1-16/
> [3] https://www.imaginationtech.com/product/img-axe-2-16/
> 
> > > Cheers,
> > > Matt
> > > 
> > > [1]: https://gitlab.freedesktop.org/imagination/linux/-/blob/b3506b8bc45ed6d4005eb32a994df0e33d6613f1/arch/arm64/boot/dts/mediatek/mt8173.dtsi#L993-1006

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