linux-kernel - Re: [PATCH] drm/msm/a6xx: Skip gpu secure fw load in EL2 mode

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Message-ID: <d788a810-1d54-48d5-a8f5-19a8e7a64313@quicinc.com>
Date: Wed, 11 Dec 2024 14:29:35 +0530
From: Pavan Kondeti <quic_pkondeti@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Pavan Kondeti <quic_pkondeti@...cinc.com>,
        Rob Clark
	<robdclark@...il.com>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        "Bjorn
 Andersson" <andersson@...nel.org>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio
	<konradybcio@...nel.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        "Marijn
 Suijten" <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Elliot Berman <quic_eberman@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/a6xx: Skip gpu secure fw load in EL2 mode

On Wed, Dec 11, 2024 at 10:52:51AM +0200, Dmitry Baryshkov wrote:
> On Wed, Dec 11, 2024 at 01:06:58PM +0530, Pavan Kondeti wrote:
> > +devicetree
> > 
> > On Tue, Dec 10, 2024 at 07:43:19PM -0800, Rob Clark wrote:
> > > On Tue, Dec 10, 2024 at 7:08 PM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
> > > >
> > > > On 12/11/2024 6:43 AM, Bjorn Andersson wrote:
> > > > > On Tue, Dec 10, 2024 at 02:22:27AM +0530, Akhil P Oommen wrote:
> > > > >> On 12/10/2024 1:24 AM, Rob Clark wrote:
> > > > >>> On Mon, Dec 9, 2024 at 12:20 AM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
> > > > >>>>
> > > > >>>> When kernel is booted in EL2, SECVID registers are accessible to the
> > > > >>>> KMD. So we can use that to switch GPU's secure mode to avoid dependency
> > > > >>>> on Zap firmware. Also, we can't load a secure firmware without a
> > > > >>>> hypervisor that supports it.
> > > > >>>
> > > > >>> Shouldn't we do this based on whether zap node is in dtb (and not disabled)?
> > > > >>
> > > > >> This is better, isn't it? Otherwise, multiple overlays should be
> > > > >> maintained for each soc/board since EL2 can be toggled from bootloader.
> > > > >> And this feature is likely going to be more widely available.
> > > > >>
> > > > >
> > > > > The DeviceTree passed to the OS needs to describe the world that said OS
> > > > > is going to operate in. If you change the world you need to change the
> > > > > description.
> > > > > There are several other examples where this would be necessary
> > > > > (remoteproc and watchdog to name two examples from the Qualcomm upstream
> > > > > world).
> > > >
> > > > But basic things work without those changes, right? For eg: Desktop UI
> > > 
> > > It isn't really so much about whether certain use-cases can work with
> > > a sub-optimal description of the hw (where in this case "hw" really
> > > means "hw plus how the fw allows things to look to the HLOS").. It is
> > > more about the hw/fw/whatever providing an accurate description of
> > > what things look like to the HLOS.
> > > 
> > > I'm leaning more towards the hw+fw providing HLOS an accurate view...
> > > and the fact that that carries over into other areas of dtb (ie. it
> > > isn't the only thing that slbounce needs to patch, as I previously
> > > mentioned) reinforces my view there.  This seems like a thing to fix
> > > in fw/bootloader tbh.
> > > 
> > 
> > Thanks Rob and Bjorn for your inputs. At the moment, we don't have
> > capability in our bootloader to apply a *specific* overlay when Linux
> > kernel is starteed in EL, this is making GPU non-functional. This patch
> > from Akhil fixes the problem without depending on the bootloader.
> > 
> > From this discussion, I understand that it is recommended to provide
> > HW+FW view in dT correctly instead of doing runtime checks in the
> > kernel. We can take this as a requirement to the bootloader.
> > 
> > I would like to check how we should proceed with overlay. Should we
> > submit dtso upstream and let bootloader apply the overlay at runtime or
> > this whole overlay needs to be maintained in the bootloader. Also,
> > Should we build all board dtb for EL2 as well or just leave it at compiling
> > the EL2 dtbo (one per SoC)?
> 
> It doesn't have to be a dtbo. Instead you might just patch the DT
> (Ideally via the https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL).
> I think the bootloader already changes the DT (by fixing memory sizes,
> etc), so enabling or disabling ZAP & fixing several other bits and
> pieces sounds logical.
> 

Yes, that would mean maintaining this completely outside upstream
kernel. As you said, this is currently happening for bootargs, memory
etc.

Thanks,
Pavan