smatch error:
drivers/gpu/drm/ast/ast_dp501.c:227 ast_launch_m68k() error:
we previously assumed 'ast->dp501_fw' could be null (see line 223)

when "!ast->dp501_fw" and "ast_load_dp501_microcode(dev) >= 0" is true,
there will be a NULL dereference of 'ast->dp501_fw'.

Fixes: 12f8030e05c6 ("drm/ast: Actually load DP501 firmware when required")
Signed-off-by: Su Hui <suhui@nfschina.com>
---
 drivers/gpu/drm/ast/ast_dp501.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_dp501.c b/drivers/gpu/drm/ast/ast_dp501.c
index 1bc35a992369..d9f3a0786a6f 100644
--- a/drivers/gpu/drm/ast/ast_dp501.c
+++ b/drivers/gpu/drm/ast/ast_dp501.c
@@ -224,8 +224,10 @@ static bool ast_launch_m68k(struct drm_device *dev)
 			    ast_load_dp501_microcode(dev) < 0)
 				return false;
 
-			fw_addr = (u8 *)ast->dp501_fw->data;
-			len = ast->dp501_fw->size;
+			if (ast->dp501_fw) {
+				fw_addr = (u8 *)ast->dp501_fw->data;
+				len = ast->dp501_fw->size;
+			}
 		}
 		/* Get BootAddress */
 		ast_moutdwm(ast, 0x1e6e2000, 0x1688a8a8);
-- 
2.30.2

Le 21/08/2023 à 08:22, Su Hui a écrit :
> smatch error:
> drivers/gpu/drm/ast/ast_dp501.c:227 ast_launch_m68k() error:
> we previously assumed 'ast->dp501_fw' could be null (see line 223)
> 
> when "!ast->dp501_fw" and "ast_load_dp501_microcode(dev) >= 0" is true,
> there will be a NULL dereference of 'ast->dp501_fw'.
> 
> Fixes: 12f8030e05c6 ("drm/ast: Actually load DP501 firmware when required")
> Signed-off-by: Su Hui <suhui@nfschina.com>
> ---
>   drivers/gpu/drm/ast/ast_dp501.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_dp501.c b/drivers/gpu/drm/ast/ast_dp501.c
> index 1bc35a992369..d9f3a0786a6f 100644
> --- a/drivers/gpu/drm/ast/ast_dp501.c
> +++ b/drivers/gpu/drm/ast/ast_dp501.c
> @@ -224,8 +224,10 @@ static bool ast_launch_m68k(struct drm_device *dev)
>   			    ast_load_dp501_microcode(dev) < 0)
>   				return false;
>   
> -			fw_addr = (u8 *)ast->dp501_fw->data;
> -			len = ast->dp501_fw->size;
> +			if (ast->dp501_fw) {
> +				fw_addr = (u8 *)ast->dp501_fw->data;
> +				len = ast->dp501_fw->size;
> +			}
>   		}
>   		/* Get BootAddress */
>   		ast_moutdwm(ast, 0x1e6e2000, 0x1688a8a8);

Hi,

this looks like a false positive.

If "!ast->dp501_fw", and ast_load_dp501_microcode()>=0, then 
ast_load_dp501_microcode() will set a valid value in ast->dp501_fw.

CJ

On 2023/8/21 15:04, Christophe JAILLET wrote:
> Le 21/08/2023 à 08:22, Su Hui a écrit :
>> smatch error:
>> drivers/gpu/drm/ast/ast_dp501.c:227 ast_launch_m68k() error:
>> we previously assumed 'ast->dp501_fw' could be null (see line 223)
>>
>> when "!ast->dp501_fw" and "ast_load_dp501_microcode(dev) >= 0" is true,
>> there will be a NULL dereference of 'ast->dp501_fw'.
>>
>> Fixes: 12f8030e05c6 ("drm/ast: Actually load DP501 firmware when 
>> required")
>> Signed-off-by: Su Hui <suhui@nfschina.com>
>> ---
>>   drivers/gpu/drm/ast/ast_dp501.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ast/ast_dp501.c 
>> b/drivers/gpu/drm/ast/ast_dp501.c
>> index 1bc35a992369..d9f3a0786a6f 100644
>> --- a/drivers/gpu/drm/ast/ast_dp501.c
>> +++ b/drivers/gpu/drm/ast/ast_dp501.c
>> @@ -224,8 +224,10 @@ static bool ast_launch_m68k(struct drm_device *dev)
>>                   ast_load_dp501_microcode(dev) < 0)
>>                   return false;
>>   -            fw_addr = (u8 *)ast->dp501_fw->data;
>> -            len = ast->dp501_fw->size;
>> +            if (ast->dp501_fw) {
>> +                fw_addr = (u8 *)ast->dp501_fw->data;
>> +                len = ast->dp501_fw->size;
>> +            }
>>           }
>>           /* Get BootAddress */
>>           ast_moutdwm(ast, 0x1e6e2000, 0x1688a8a8);
>
> Hi,
>
> this looks like a false positive.
>
> If "!ast->dp501_fw", and ast_load_dp501_microcode()>=0, then 
> ast_load_dp501_microcode() will set a valid value in ast->dp501_fw.

Hi,

Sorry for the noise, you are right, this is a false positive.
I will take more careful next time.

Su Hui

>
> CJ