Re: [PATCH v2 04/10] drm/simpledrm: Compute framebuffer stride if not set

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi Daniel

Am 11.08.22 um 19:23 schrieb Daniel Vetter:
> On Wed, 27 Jul 2022 at 09:53, Thomas Zimmermann <tzimmermann@suse.de> wrote:
>>
>> Hi
>>
>> Am 25.07.22 um 17:13 schrieb Javier Martinez Canillas:
>>> Hello Geert,
>>>
>>> On 7/21/22 16:46, Geert Uytterhoeven wrote:
>>>> Hi Thomas,
>>>>
>>>> On Wed, Jul 20, 2022 at 4:27 PM Thomas Zimmermann <tzimmermann@suse.de> wrote:
>>>>> Compute the framebuffer's scanline stride length if not given by
>>>>> the simplefb data.
>>>>>
>>>>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>>>>
>>>> Thanks for your patch!
>>>>
>>>>> --- a/drivers/gpu/drm/tiny/simpledrm.c
>>>>> +++ b/drivers/gpu/drm/tiny/simpledrm.c
>>>>> @@ -743,6 +743,9 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
>>>>>                   drm_err(dev, "no simplefb configuration found\n");
>>>>>                   return ERR_PTR(-ENODEV);
>>>>>           }
>>>>> +       if (!stride)
>>>>> +               stride = format->cpp[0] * width;
>>>>
>>>> DIV_ROUND_UP(drm_format_info_bpp(format) * width, 8)
>>>>
>>>
>>> I think you meant here:
>>>
>>> DIV_ROUND_UP(drm_format_info_bpp(format, 0) * width, 8) ?
>>
>> I guess, that's the right function. My original code is correct, but cpp
>> is also deprecated.
> 
> You all mean drm_format_info_min_pitch().

Thanks a lot. I wasn't even aware of this function, but I had almost 
written my own implementation of it.  I'll update the patch accordingly.

Best regards
Thomas

> 
> I really don't want drivers to go grab any of the legacy format info
> fields like bpp or depth. switch() statements on the fourcc code for
> programming registers, or one of the real helper functions in
> drm_fourcc.c (there might be some gaps), but not ever going through
> legacy concepts. Anything else just leads to subtle bugs when new
> formats get added and oops suddenly the assumptions don't hold.
> 
> Those should be strictly limited to legacy (i.e. not drm_fourcc aware)
> interfaces. Heck I think even fbdev emulation should completely switch
> over to drm_fourcc/drm_format_info, but alas that's a pile of work and
> not much payoff.
> 
> I'm trying to volunteer Same to add a legacy_bpp tag to the above
> helper and appropriately limit it, I think limiting to formats with
> depth!=0 is probably the right thing. And then we should probably
> remove a pile of the cargo-culted depth!=0 entries too.
> -Daniel
> 
>>
>> Best regards
>> Thomas
>>
>>>
>>> With that change,
>>>
>>> Acked-by: Javier Martinez Canillas <javierm@redhat.com>
>>>
>>
>> --
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Maxfeldstr. 5, 90409 Nürnberg, Germany
>> (HRB 36809, AG Nürnberg)
>> Geschäftsführer: Ivo Totev
> 
> 
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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