Hi
Am 10.09.19 um 13:52 schrieb Gerd Hoffmann:
> On Mon, Sep 09, 2019 at 04:06:32PM +0200, Thomas Zimmermann wrote:
>> Before updating the display from the console's shadow buffer, the dirty
>> worker now waits for vblank. This allows several screen updates to pile
>> up and acts as a rate limiter.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
>> ---
>> drivers/gpu/drm/drm_fb_helper.c | 12 ++++++++++++
>> 1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>> index a7ba5b4902d6..017e2f6bd1b9 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -402,8 +402,20 @@ static void drm_fb_helper_dirty_work(struct work_struct *work)
>> dirty_work);
>> struct drm_clip_rect *clip = &helper->dirty_clip;
>> struct drm_clip_rect clip_copy;
>> + struct drm_crtc *crtc;
>> unsigned long flags;
>> void *vaddr;
>> + int ret;
>> +
>> + /* rate-limit update frequency */
>> + mutex_lock(&helper->lock);
>> + crtc = helper->client.modesets[0].crtc;
>> + ret = drm_crtc_vblank_get(crtc);
>> + if (!ret) {
>> + drm_crtc_wait_one_vblank(crtc);
>> + drm_crtc_vblank_put(crtc);
>> + }
>> + mutex_unlock(&helper->lock);
>
> Hmm, not sure it is the best plan to sleep for a while in the worker,
> especially while holding the lock.
>
> What does the lock protect against here? Accessing
This lock is hold by the fbdev code during mode-setting operations (but
not drawing operations). So *crtc might be gone if we don't hold it here.
> helper->client.modesets? If so then you can unlock before going to
> sleep in drm_crtc_wait_one_vblank() I think.
I looked, but I cannot find any code that protects crtc while vblank is
active. I'd rather not change the current code until someone can clarify.
Best regards
Thomas
>
> cheers,
> Gerd
>
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)
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