[PATCH v3 02/81] drm/fbdev-helper: Set and clear VGA switcheroo client from fb_info

[Javier Martinez Canillas]

Thomas Zimmermann <tzimmermann at suse.de> writes:

> Hi Javier
>
> Am 03.09.24 um 12:18 schrieb Javier Martinez Canillas:
>> Thomas Zimmermann <tzimmermann at suse.de> writes:
>>
>> Hello Thomas,
>>
>>> Call vga_switcheroo_client_fb_set() with the PCI device from the
>>> instance of struct fb_info. All fbdev clients now run these calls.
>>> For non-PCI devices or drivers without vga-switcheroo, this does
>>> nothing. For i915 and radeon, it allows these drivers to use a
>>> common fbdev client.
>>>
>>> The device is the same as the one stored in struct drm_client and
>>> struct drm_fb_helper, so there is no difference in behavior. Some
>>> NULL-pointer checks are being removed, where those pointers cannot
>>> be NULL.
>>>
>>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>>> ---
>>>   drivers/gpu/drm/drm_fb_helper.c | 15 +++++++++++----
>>>   1 file changed, 11 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>>> index af1fe79c701d..13095d38aa42 100644
>>> --- a/drivers/gpu/drm/drm_fb_helper.c
>>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>>> @@ -562,8 +562,12 @@ EXPORT_SYMBOL(drm_fb_helper_release_info);
>>>    */
>>>   void drm_fb_helper_unregister_info(struct drm_fb_helper *fb_helper)
>>>   {
>>> -	if (fb_helper && fb_helper->info)
>>> -		unregister_framebuffer(fb_helper->info);
>> I'm not sure if we can assume these won't be NULL... AFAICT some drivers
>> still have their own struct drm_client_funcs vtable and could potentially
>> pass a NULL struct drm_fb_helper ?
>
> I did a
>
>    git grep -B4 drm_fb_helper_unregister_info
>
> on drm-tip and all callers, such as [1], test fb_helper->info before 
> calling the function. So it's safe to remove the test.
>

Yes, I also noticed that all callers were already checking if is not NULL
but still is more robust for the function to check it in case there is a
bug in a driver.

But as a said, I'm OK with dropping it as long as it is mentioned in the
kernel-doc that the parameter must not be NULL.

> [1] 
> https://elixir.bootlin.com/linux/v6.10/source/drivers/gpu/drm/drm_fbdev_dma.c#L162
>
>>
>> If you think that's safe to do this and the function semantics should be
>> changed, then I think that the kernel-doc needs to be updated:
>>
>> - * @fb_helper: driver-allocated fbdev helper, can be NULL
>> + * @fb_helper: driver-allocated fbdev helper, must not be NULL
>
> Ok.
>
>>
>> Other than that, the patch looks good to me:
>>
>> Reviewed-by: Javier Martinez Canillas <javierm at redhat.com>
>
> Thanks.
>
> Best regards
> Thomas
>
>>
>
> -- 
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Frankenstrasse 146, 90461 Nuernberg, Germany
> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
> HRB 36809 (AG Nuernberg)
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat