linux-kernel - Re: [PATCH] drm/msm/a6xx: fix for kernels without CONFIG

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Message-ID: <CAF6AEGv-A5=4z7ZO-SytmivZTfKPYxhAjmRLVsQnrT7_pYCDtQ@mail.gmail.com>
Date:   Fri, 19 Feb 2021 08:00:53 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Akhil P Oommen <akhilpo@...eaurora.org>
Cc:     Jonathan Marek <jonathan@...ek.ca>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Eric Anholt <eric@...olt.net>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/a6xx: fix for kernels without CONFIG_NVMEM

On Fri, Feb 19, 2021 at 2:44 AM Akhil P Oommen <akhilpo@...eaurora.org> wrote:
>
> On 2/18/2021 9:41 PM, Rob Clark wrote:
> > On Thu, Feb 18, 2021 at 4:28 AM Akhil P Oommen <akhilpo@...eaurora.org> wrote:
> >>
> >> On 2/18/2021 2:05 AM, Jonathan Marek wrote:
> >>> On 2/17/21 3:18 PM, Rob Clark wrote:
> >>>> On Wed, Feb 17, 2021 at 11:08 AM Jordan Crouse
> >>>> <jcrouse@...eaurora.org> wrote:
> >>>>>
> >>>>> On Wed, Feb 17, 2021 at 07:14:16PM +0530, Akhil P Oommen wrote:
> >>>>>> On 2/17/2021 8:36 AM, Rob Clark wrote:
> >>>>>>> On Tue, Feb 16, 2021 at 12:10 PM Jonathan Marek <jonathan@...ek.ca>
> >>>>>>> wrote:
> >>>>>>>>
> >>>>>>>> Ignore nvmem_cell_get() EOPNOTSUPP error in the same way as a
> >>>>>>>> ENOENT error,
> >>>>>>>> to fix the case where the kernel was compiled without CONFIG_NVMEM.
> >>>>>>>>
> >>>>>>>> Fixes: fe7952c629da ("drm/msm: Add speed-bin support to a618 gpu")
> >>>>>>>> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> >>>>>>>> ---
> >>>>>>>>    drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 6 +++---
> >>>>>>>>    1 file changed, 3 insertions(+), 3 deletions(-)
> >>>>>>>>
> >>>>>>>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> >>>>>>>> b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> >>>>>>>> index ba8e9d3cf0fe..7fe5d97606aa 100644
> >>>>>>>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> >>>>>>>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> >>>>>>>> @@ -1356,10 +1356,10 @@ static int a6xx_set_supported_hw(struct
> >>>>>>>> device *dev, struct a6xx_gpu *a6xx_gpu,
> >>>>>>>>
> >>>>>>>>           cell = nvmem_cell_get(dev, "speed_bin");
> >>>>>>>>           /*
> >>>>>>>> -        * -ENOENT means that the platform doesn't support
> >>>>>>>> speedbin which is
> >>>>>>>> -        * fine
> >>>>>>>> +        * -ENOENT means no speed bin in device tree,
> >>>>>>>> +        * -EOPNOTSUPP means kernel was built without CONFIG_NVMEM
> >>>>>>>
> >>>>>>> very minor nit, it would be nice to at least preserve the gist of the
> >>>>>>> "which is fine" (ie. some variation of "this is an optional thing and
> >>>>>>> things won't catch fire without it" ;-))
> >>>>>>>
> >>>>>>> (which is, I believe, is true, hopefully Akhil could confirm.. if not
> >>>>>>> we should have a harder dependency on CONFIG_NVMEM..)
> >>>>>> IIRC, if the gpu opp table in the DT uses the 'opp-supported-hw'
> >>>>>> property,
> >>>>>> we will see some error during boot up if we don't call
> >>>>>> dev_pm_opp_set_supported_hw(). So calling "nvmem_cell_get(dev,
> >>>>>> "speed_bin")"
> >>>>>> is a way to test this.
> >>>>>>
> >>>>>> If there is no other harm, we can put a hard dependency on
> >>>>>> CONFIG_NVMEM.
> >>>>>
> >>>>> I'm not sure if we want to go this far given the squishiness about
> >>>>> module
> >>>>> dependencies. As far as I know we are the only driver that uses this
> >>>>> seriously
> >>>>> on QCOM SoCs and this is only needed for certain targets. I don't
> >>>>> know if we
> >>>>> want to force every target to build NVMEM and QFPROM on our behalf.
> >>>>> But maybe
> >>>>> I'm just saying that because Kconfig dependencies tend to break my
> >>>>> brain (and
> >>>>> then Arnd has to send a patch to fix it).
> >>>>>
> >>>>
> >>>> Hmm, good point.. looks like CONFIG_NVMEM itself doesn't have any
> >>>> other dependencies, so I suppose it wouldn't be the end of the world
> >>>> to select that.. but I guess we don't want to require QFPROM
> >>>>
> >>>> I guess at the end of the day, what is the failure mode if you have a
> >>>> speed-bin device, but your kernel config misses QFPROM (and possibly
> >>>> NVMEM)?  If the result is just not having the highest clk rate(s)
> >>
> >> Atleast on sc7180's gpu, using an unsupported FMAX breaks gmu. It won't
> >> be very obvious what went wrong when this happens!
> >
> > Ugg, ok..
> >
> > I suppose we could select NVMEM, but not QFPROM, and then the case
> > where QFPROM is not enabled on platforms that have the speed-bin field
> > in DT will fail gracefully and all other platforms would continue on
> > happily?
> >
> > BR,
> > -R
>
> Sounds good to me.
>

You probably should do a quick test with NVMEM enabled but QFPROM
disabled to confirm my theory, but I *think* that should work

BR,
-R