Re: [PATCH] drm/amdgpu/display: add fallthrough comment

[Harry Wentland <hwentlan@amd.com>]

On 2019-12-05 5:16 p.m., Liu, Zhan wrote:
> 
> 
>> -----Original Message-----
>> From: Alex Deucher <alexdeucher@gmail.com>
>> Sent: 2019/December/05, Thursday 5:13 PM
>> To: Liu, Zhan <Zhan.Liu@amd.com>
>> Cc: amd-gfx@lists.freedesktop.org; Deucher, Alexander
>> <Alexander.Deucher@amd.com>
>> Subject: Re: [PATCH] drm/amdgpu/display: add fallthrough comment
>>
>> On Thu, Dec 5, 2019 at 5:10 PM Liu, Zhan <Zhan.Liu@amd.com> wrote:
>>>
>>>
>>>
>>>> -----Original Message-----
>>>> From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of
>>>> Alex Deucher
>>>> Sent: 2019/December/05, Thursday 4:39 PM
>>>> To: amd-gfx@lists.freedesktop.org
>>>> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>
>>>> Subject: [PATCH] drm/amdgpu/display: add fallthrough comment
>>>>
>>>> To avoid a compiler warning.
>>>>
>>>> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
>>>> ---
>>>>  drivers/gpu/drm/amd/display/dc/dce/dce_aux.c | 1 +
>>>>  1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_aux.c
>>>> b/drivers/gpu/drm/amd/display/dc/dce/dce_aux.c
>>>> index 191b68b8163a..f1a5d2c6aa37 100644
>>>> --- a/drivers/gpu/drm/amd/display/dc/dce/dce_aux.c
>>>> +++ b/drivers/gpu/drm/amd/display/dc/dce/dce_aux.c
>>>> @@ -645,6 +645,7 @@ bool dce_aux_transfer_with_retries(struct
>>>> ddc_service *ddc,
>>>>                       case AUX_TRANSACTION_REPLY_AUX_DEFER:
>>>>                       case
>>>> AUX_TRANSACTION_REPLY_I2C_OVER_AUX_DEFER:
>>>>                               retry_on_defer = true;
>>>> +                             /* fall through */
>>>
>>> I am a bit confusing here. Why a comment can avoid a compiler warning?
>>
>> The kernel enables fall through warnings, so unless there is a comment
>> mentioning that are are expecting to fall through here, we get a warning.
>> The idea is to find missing breaks in switch code.
>>
>> Alex
> 
> Got you. Thank you for your explanation.
> 
> Reviewed-by: Zhan Liu <zhan.liu@amd.com>
> 

Interesting. It's described at [1] (search for
-Wimplicit-fallthrough=3). Never knew that.

This is also
Reviewed-by: Harry Wentland <harry.wentland@amd.com>

[1]
https://developers.redhat.com/blog/2017/03/10/wimplicit-fallthrough-in-gcc-7/

Harry

>>
>>>
>>>>                       case
>>>> AUX_TRANSACTION_REPLY_I2C_OVER_AUX_NACK:
>>>>                               if (++aux_defer_retries >=
>>>> AUX_MAX_DEFER_RETRIES) {
>>>>                                       goto fail;
>>>> --
>>>> 2.23.0
>>>>
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