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Subject: Re: [PATCH] drm/msm/a6xx: fix for kernels without CONFIG_NVMEM
To:     Rob Clark <robdclark@gmail.com>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Jonathan Marek <jonathan@marek.ca>,
        freedreno <freedreno@lists.freedesktop.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <dri-devel@lists.freedesktop.org>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@vger.kernel.org>, Sean Paul <sean@poorly.run>
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From:   Akhil P Oommen <akhilpo@codeaurora.org>
Message-ID: <fed21bb2-77ee-107c-a7fc-1f0965334da1@codeaurora.org>
Date:   Sat, 3 Apr 2021 10:09:49 +0530
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On 4/2/2021 3:19 AM, Rob Clark wrote:
> On Thu, Apr 1, 2021 at 2:03 PM Dmitry Baryshkov
> <dmitry.baryshkov@linaro.org> wrote:
>>
>> On Thu, 1 Apr 2021 at 23:09, Rob Clark <robdclark@gmail.com> wrote:
>>>
>>> On Mon, Feb 22, 2021 at 8:06 AM Rob Clark <robdclark@gmail.com> wrote:
>>>>
>>>> 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
>>>>
>>>
>>> btw, did anyone ever send a patch to select NVMEM?  I'm not seeing one
>>> but I could be overlooking something
I thought Jonathan would send it as the discussion was going on in his 
patch. No problem, I will send it out. :)

-Akhil.

>>
>> Judging by the amount of issues surrounding speed-bin, I might have a
>> bold suggestion to revert these patches for now and get them once all
>> the issues are sorted, so that we'd have a single working commit
>> instead of scattered patch series breaking git bisect, having bad
>> side-effects on non-sc7180 platforms, etc.
>>
> 
> We do really need some pre-merge CI like we have on the mesa side of
> things (and we at least have 845 devices in our CI farm, but it would
> be useful to add more generations)..  but other than the config issue,
> I *think* this fixes the last of the speedbin fallout?
> 
> https://patchwork.freedesktop.org/patch/426538/?series=88558&rev=1
> 
> Planning to include that in a -fixes pull req in the next day or two.
> (And please have a look at msm-next-staging and let me know if you see
> anything other fixes that would be good to get in, speedbin related or
> otherwise.)
> 
> BR,
> -R
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