On 2019-07-19 2:37 p.m., Daniel Vetter wrote: > On Fri, Jul 19, 2019 at 1:32 PM Sam Ravnborg <sam@xxxxxxxxxxxx> wrote: >> On Fri, Jul 19, 2019 at 11:05:44AM +0200, Michel Dänzer wrote: >>> On 2019-07-19 8:07 a.m., Sam Ravnborg wrote: >>>> On Thu, Jul 18, 2019 at 05:37:31PM +0200, Sam Ravnborg wrote: >>>>> This is some janitorial updates to the via driver >>>>> that is required to get rid of deprecated headers >>>>> in the drm subsystem. >>>>> >>>>> The first three patches are trivial, where >>>>> the dependencies on drmP.h and drm_os_linux are dropped. >>>>> >>>>> The remaining three patches drop use of DRM_WAIT_ON(). >>>>> They are replaced by wait_event_interruptible_timeout(). >>>>> These patches could use a more critical review. >>>> >>>> The differences between DRM_WAIT_ON() and >>>> wait_event_interruptible_timeout() are bigger than anticipated. >>>> >>>> The conversion I did for drm_vblank.c is bogus thus I expect >>>> the conversion done for via is also bogus. >>> >>> What exactly is the problem though? Can you share information about the >>> failures you're seeing? >>> >>> There was some discussion about DRM_WAIT_ON() "polling" on IRC. I assume >>> that refers to it only sleeping for up to 0.01s before checking the >>> condition again. In contrast, wait_event_interruptible_timeout() checks >>> the condition once, then sleeps up to the full timeout before checking >>> it again. >> Correct - it was based on the feedback on irc from airlied and ickle >> that made me conclude that the via part may not be good. >> I cannot say if the polling versus timeout is properly dealt with in the >> via driver and I am inclided to just move DRM_WAIT_ON() to via_drv.h and >> name it VIA_WAIT_ON(). >> Then the changes to this legacy driver is minimal and it will not >> prevent us from gettting rid of drm_os_linux.h >> >>> >>> If that makes a difference for drm_wait_vblank_ioctl, it indicates that >>> some other code which updates the vblank count or clears vblank->enabled >>> doesn't wake up the vblank->queue. >> Let me analyse a little... >> >> In drm_handle_vblank() there is a call to wake_up(&vblank->queue); >> And this is called from an interrupt - OK. I'm not sure why it's relevant whether or not a function can be called from an interrupt handler. >> drm_vblank_enable() is called outside an interrupt - no need for >> wake_up() There is no need here because there can be no sleeping waiters in the queue, because vblank->enabled == false immediately terminates any waits. >> drm_crtc_accurate_vblank_count() is called outside interrupt - no need >> for wake_up() This is called from interrupt handlers, at least from amdgpu_dm.c:dm_pflip_high_irq(). Not sure it needs to wake up the queue though, the driver should call drm_(crtc_)_handle_vblank anyway. >> drm_vblank_disable_and_save() is called outside interrupt - no need for >> wake_up()' It can be called from an interrupt, via drm_handle_vblank -> vblank_disable_fn. However, the only place where drm_vblank_disable_and_save can be called with sleeping waiters in the queue is in drm_crtc_vblank_off, which wakes up the queue afterwards (which terminates all waits, because vblank->enabled == false at this point). >> That is all functions I could dig up that updates the vblank counter. I agree, this should also cover everything which clears vblank->enabled. So, are there still failures with v2 of the drm_wait_vblank_ioctl patch (which I haven't seen after all BTW)? If yes, can you share information about them? If not, why do you want to send a v3? -- Earthling Michel Dänzer | https://www.amd.com Libre software enthusiast | Mesa and X developer _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
