[PATCH 4/5] drm/fb-helper: Clip damage area to written memory range

[Thomas Zimmermann]

Hi

Am 09.02.22 um 12:09 schrieb Javier Martinez Canillas:
> On 2/6/22 20:29, Thomas Zimmermann wrote:
>> Write helpers used to mark the complete screen as dirty. This is
>> wasteful for writes that only change a small portion of the screen.
>> Fix the problem by computing the damaged area from the written
>> memory range and perform damage handling accordingly.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>> ---
> 
> Reviewed-by: Javier Martinez Canillas <javierm at redhat.com>
> 
>>   drivers/gpu/drm/drm_fb_helper.c | 28 +++++++++++++++++++++-------
>>   1 file changed, 21 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>> index ae98990c7b66..bed58be1b205 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -754,11 +754,18 @@ EXPORT_SYMBOL(drm_fb_helper_sys_read);
>>   ssize_t drm_fb_helper_sys_write(struct fb_info *info, const char __user *buf,
>>   				size_t count, loff_t *ppos)
>>   {
>> +	loff_t pos = *ppos;
>>   	ssize_t ret;
>> +	struct drm_rect damage_area;
>>   
>>   	ret = fb_sys_write(info, buf, count, ppos);
>> -	if (ret > 0)
>> -		drm_fb_helper_damage(info, 0, 0, info->var.xres, info->var.yres);
>> +	if (ret <= 0)
>> +		return ret;
>> +
> 
> I also like how you cleaned up the error checking here and below
> to just return early, instead of checking if ret > 0 to perform
> the damage handling.

It's more readable now IMHO. And I think I read that compilers or CPUs 
expect this test to fail by default in their branch prediction. So it 
might even be faster by a few cycles.

Best regards
Thomas

> 
> Best regards,

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature
Type: application/pgp-signature
Size: 840 bytes
Desc: OpenPGP digital signature
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20220209/a6215086/attachment.sig>