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

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Message-ID: <775436ba-c94a-ab22-d65b-b2391047ec65@codeaurora.org>
Date:   Wed, 17 Feb 2021 19:14:16 +0530
From:   Akhil P Oommen <akhilpo@...eaurora.org>
To:     Rob Clark <robdclark@...il.com>, Jonathan Marek <jonathan@...ek.ca>
Cc:     freedreno <freedreno@...ts.freedesktop.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Eric Anholt <eric@...olt.net>,
        Sharat Masetty <smasetty@...eaurora.org>,
        "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 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.

-Akhil.
> 
> BR,
> -R
> 
>>           */
>> -       if (PTR_ERR(cell) == -ENOENT)
>> +       if (PTR_ERR(cell) == -ENOENT || PTR_ERR(cell) == -EOPNOTSUPP)
>>                  return 0;
>>          else if (IS_ERR(cell)) {
>>                  DRM_DEV_ERROR(dev,
>> --
>> 2.26.1
>>