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In-Reply-To: <0f057c99-ec94-f3e3-796f-b73a609f735d@codeaurora.org>
From:   Rob Clark <robdclark@gmail.com>
Date:   Mon, 22 Feb 2021 08:06:38 -0800
Message-ID: <CAF6AEGvXYmcj0YuciZATveALJEP6DdFiwmtnYevrK2SEOJNZGg@mail.gmail.com>
Subject: Re: [PATCH] drm/msm/a6xx: fix for kernels without CONFIG_NVMEM
To:     Akhil P Oommen <akhilpo@codeaurora.org>
Cc:     Jonathan Marek <jonathan@marek.ca>,
        freedreno <freedreno@lists.freedesktop.org>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Eric Anholt <eric@anholt.net>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@vger.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <dri-devel@lists.freedesktop.org>,
        open list <linux-kernel@vger.kernel.org>
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On Mon, Feb 22, 2021 at 7:45 AM Akhil P Oommen <akhilpo@codeaurora.org> wrote:
>
> On 2/19/2021 9:30 PM, Rob Clark wrote:
> > On Fri, Feb 19, 2021 at 2:44 AM Akhil P Oommen <akhilpo@codeaurora.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@codeaurora.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@codeaurora.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@marek.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@marek.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
> >
>
> I tried it on an sc7180 device. The suggested combo (CONFIG_NVMEM + no
> CONFIG_QCOM_QFPROM) makes the gpu probe fail with error "failed to read
> speed-bin. Some OPPs may not be supported by hardware". This is good
> enough clue for the developer that he should fix the broken speedbin
> detection.
>

Ok, great.. then sounds like selecting NVMEM is a good approach

BR,
-R