linux-kernel - Re: [PATCH] drm/msm: Fix return type of mdp4_lvds_connector_mode

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Message-ID: <1c735bcc-d4f7-333f-58a5-e3f463bab10d@linaro.org>
Date:   Tue, 1 Nov 2022 03:24:29 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Nathan Chancellor <nathan@...nel.org>,
        Nathan Huckleberry <nhuck@...gle.com>
Cc:     Dan Carpenter <error27@...il.com>, llvm@...ts.linux.dev,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm: Fix return type of
 mdp4_lvds_connector_mode_valid

On 01/11/2022 01:10, Nathan Chancellor wrote:
> On Tue, Sep 13, 2022 at 01:55:48PM -0700, Nathan Huckleberry wrote:
>> The mode_valid field in drm_connector_helper_funcs is expected to be of
>> type:
>> enum drm_mode_status (* mode_valid) (struct drm_connector *connector,
>>                                       struct drm_display_mode *mode);
>>
>> The mismatched return type breaks forward edge kCFI since the underlying
>> function definition does not match the function hook definition.
>>
>> The return type of mdp4_lvds_connector_mode_valid should be changed from
>> int to enum drm_mode_status.
>>
>> Reported-by: Dan Carpenter <error27@...il.com>
>> Link: https://github.com/ClangBuiltLinux/linux/issues/1703
>> Cc: llvm@...ts.linux.dev
>> Signed-off-by: Nathan Huckleberry <nhuck@...gle.com>
>> ---
>>   drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c b/drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c
>> index 7288041dd86a..7444b75c4215 100644
>> --- a/drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c
>> +++ b/drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c
>> @@ -56,8 +56,9 @@ static int mdp4_lvds_connector_get_modes(struct drm_connector *connector)
>>   	return ret;
>>   }
>>   
>> -static int mdp4_lvds_connector_mode_valid(struct drm_connector *connector,
>> -				 struct drm_display_mode *mode)
>> +static enum drm_mode_status
>> +mdp4_lvds_connector_mode_valid(struct drm_connector *connector,
>> +			       struct drm_display_mode *mode)
>>   {
>>   	struct mdp4_lvds_connector *mdp4_lvds_connector =
>>   			to_mdp4_lvds_connector(connector);
>> -- 
>> 2.37.2.789.g6183377224-goog
>>
>>
> 
> Did this patch get lost somewhere? I do not see it picked up. It is
> needed to avoid a new WIP warning from clang for catching these CFI
> failures:
> 
> drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c:89:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_connector *, struct drm_display_mode *)' with an expression of type 'int (struct drm_connector *, struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
>          .mode_valid = mdp4_lvds_connector_mode_valid,
>                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 1 error generated.

It will be picked into 6.1-rc and then propagate through the stable 
kernel updates.

Anyway:

Fixes: 3e87599b68e7 ("drm/msm/mdp4: add LVDS panel support")
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>


-- 
With best wishes
Dmitry