linux-kernel - Re: [PATCH] drm/amd/display: Change status's type in aux_reply_transaction

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Date:   Thu, 27 Sep 2018 06:03:56 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     sunpeng.li@....com, alexander.deucher@....com,
        christian.koenig@....com, David1.Zhou@....com,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/amd/display: Change status's type in
 aux_reply_transaction_data

On 2018-09-24 06:22 PM, Nathan Chancellor wrote:
> On Mon, Sep 24, 2018 at 03:07:16PM -0700, Nick Desaulniers wrote:
>> On Fri, Sep 21, 2018 at 2:55 PM Nathan Chancellor
>> <natechancellor@...il.com> wrote:
>>>
>>> Clang warns when one enumerated type is implicitly converted to another.
>>>
>>> drivers/gpu/drm/amd/amdgpu/../display/dc/dce/dce_aux.c:315:19: warning:
>>> implicit conversion from enumeration type 'enum
>>> aux_channel_operation_result' to different enumeration type 'enum
>>> aux_transaction_reply' [-Wenum-conversion]
>>>                 reply->status = AUX_CHANNEL_OPERATION_FAILED_HPD_DISCON;
>>>                               ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> drivers/gpu/drm/amd/amdgpu/../display/dc/i2caux/dce110/aux_engine_dce110.c:349:19:
>>> warning: implicit conversion from enumeration type 'enum
>>> aux_channel_operation_result' to different enumeration type 'enum
>>> aux_transaction_reply' [-Wenum-conversion]
>>>                 reply->status = AUX_CHANNEL_OPERATION_FAILED_HPD_DISCON;
>>>                               ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> I think the enum is actually wrong here.  I think the correct fix would be:
>>
>> -                 reply->status = AUX_CHANNEL_OPERATION_FAILED_HPD_DISCON;
>> +                 reply->status = AUX_TRANSACTION_REPLY_HPD_DISCON;
>>
>> The identifiers are so similar, my guess was that it was easy to mix
>> them up.  This looks like an actual bug to me, since the identifiers
>> have different values between the 2 different enums.
>>
> 
> Hmmm interesting... I will be happy to send a v2 with your suggestion if
> one of the maintainers could confirm that to be the case (given DRM code
> is rather dense).
> 

Nick is correct. We should keep the enum but assign AUX_TRANSACTION_REPLY_HPD_DISCON in dce_aux.c and aux_engine_dce110.c.

Thanks for spotting this.

Harry

> Thanks for the review!
> Nathan
> 
>>>
>>> Instead of implicitly or explicitly converting between types, just
>>> change status to type uint8_t (since its max size is 255) which avoids
>>> this construct altogether.
>>>
>>> Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
>>> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
>>> ---
>>>  drivers/gpu/drm/amd/display/dc/dc_ddc_types.h | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/display/dc/dc_ddc_types.h b/drivers/gpu/drm/amd/display/dc/dc_ddc_types.h
>>> index 05c8c31d8b31..97e1d4d19263 100644
>>> --- a/drivers/gpu/drm/amd/display/dc/dc_ddc_types.h
>>> +++ b/drivers/gpu/drm/amd/display/dc/dc_ddc_types.h
>>> @@ -79,7 +79,7 @@ enum aux_transaction_reply {
>>>  };
>>>
>>>  struct aux_reply_transaction_data {
>>> -       enum aux_transaction_reply status;
>>> +       uint8_t status;
>>>         uint32_t length;
>>>         uint8_t *data;
>>>  };
>>> --
>>> 2.19.0
>>>
>>
>>
>> -- 
>> Thanks,
>> ~Nick Desaulniers