From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= Subject: Re: [PATCH] drm/vkms: Solve bug on kms_crc_cursor tests Date: Mon, 11 Mar 2019 16:27:10 +0200 Message-ID: <20190311142710.GY3888@intel.com> References: <20190225142606.gov32asdq3qe375q@smtp.gmail.com> <20190228101107.GL2665@phenom.ffwll.local> <20190228140341.GG20097@intel.com> <20190301152558.GR20097@intel.com> <20190301184147.GS20097@intel.com> <20190310203505.2needmil76a4rc74@smtp.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <20190310203505.2needmil76a4rc74@smtp.gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Rodrigo Siqueira Cc: Shayenne Moura , Haneen Mohammed , David Airlie , dri-devel , Linux Kernel Mailing List List-Id: dri-devel@lists.freedesktop.org On Sun, Mar 10, 2019 at 05:35:05PM -0300, Rodrigo Siqueira wrote: > On 03/01, Ville Syrjälä wrote: > > On Fri, Mar 01, 2019 at 03:35:35PM -0300, Shayenne Moura wrote: > > > Em sex, 1 de mar de 2019 às 12:26, Ville Syrjälä > > > escreveu: > > > > > > > > On Fri, Mar 01, 2019 at 11:55:11AM -0300, Shayenne Moura wrote: > > > > > Em qui, 28 de fev de 2019 às 11:03, Ville Syrjälä > > > > > escreveu: > > > > > > > > > > > > On Thu, Feb 28, 2019 at 11:11:07AM +0100, Daniel Vetter wrote: > > > > > > > On Mon, Feb 25, 2019 at 11:26:06AM -0300, Shayenne Moura wrote: > > > > > > > > vkms_crc_work_handle needs the value of the actual frame to > > > > > > > > schedule the workqueue that calls periodically the vblank > > > > > > > > handler and the destroy state functions. However, the frame > > > > > > > > value returned from vkms_vblank_simulate is updated and > > > > > > > > diminished in vblank_get_timestamp because it is not in a > > > > > > > > vblank interrupt, and return an inaccurate value. > > > > > > > > > > > > > > > > Solve this getting the actual vblank frame directly from the > > > > > > > > vblank->count inside the `struct drm_crtc`, instead of using > > > > > > > > the `drm_accurate_vblank_count` function. > > > > > > > > > > > > > > > > Signed-off-by: Shayenne Moura > > > > > > > > > > > > > > Sorry for the delay, I'm a bit swamped right now :-/ > > > > > > > > > > > > > > Debug work you're doing here is really impressive! But I have no idea > > > > > > > what's going on. It doesn't look like it's just papering over a bug (like > > > > > > > the in_vblank_irq check we've discussed on irc), but I also have no idea > > > > > > > why it works. > > > > > > > > > > > > > > I'll pull in Ville, he understands this better than me. > > > > > > > > > > > > It's not entirely clear what we're trying to fix. From what I can see > > > > > > the crc work seems to be in no way synchronized with page flips, so > > > > > > I'm not sure how all this is really supposed to work. > > > > > > > > > > > > > > > > Hi, Ville! > > > > > > > > > > Thank you for the review! :) > > > > > > > > > > I do not understand well what crc code is doing, but the issue that I found > > > > > is related to the vblank timestamp and frame count. > > > > > > > > > > When vkms handles the crc_cursor it uses the start frame and end frame > > > > > values to verify if it needs to call the function 'drm_crtc_add_crc_entry()' > > > > > for each frame. > > > > > > > > > > However, when getting the frame count, the code is calling the function > > > > > drm_update_vblank_count(dev, pipe, false) and, because of the 'false', > > > > > subtracting the actual vblank timestamp (consequently, the frame count > > > > > value), causing conflicts. > > > > > > > > The in_vblank_irq behavour looks sane to me. What are these conflicts? > > > > > > > > > > The entire history was: > > > - I sent the patch with bugfix for vblank extra frame. The patch changed > > > our function vkms_get_vblank_timestamp() to look like this: > > > > > > bool vkms_get_vblank_timestamp(struct drm_device *dev, unsigned int pipe, > > > int *max_error, ktime_t *vblank_time, > > > bool in_vblank_irq) > > > { > > > struct vkms_device *vkmsdev = drm_device_to_vkms_device(dev); > > > struct vkms_output *output = &vkmsdev->output; > > > > > > *vblank_time = output->vblank_hrtimer.node.expires; > > > > > > + if (!in_vblank_irq) > > > + *vblank_time -= output->period_ns; > > > > > > return true; > > > } > > > > > > - This patch solve the issue that I was looking for (extra vblank > > > frames on kms_flip). > > > > > > - However, kms_cursor_crc tests, which passed before my patch, started to fail. > > > > > > - Debugging them, I found that the problem was inside of function > > > `vkms_vblank_simulate()` > > > when it was handling the crc_enabled (inside if (state && output->crc_enabled)) > > > and inside the function vkms_crc_work_handle() too. > > > > > > - Following the steps: > > > 1. Inside vkms_vblank_simulate() we call drm_crtc_accurate_vblank_count() > > > 2. In its turn, drm_crtc_accurate_vblank_count() calls the function > > > drm_update_vblank_count(dev, pipe, false). /* This false is default */ > > > 3. Finally, the “false” used in drm_update_vblank_count(), will be > > > passed to vkms_get_vblank_timestamp() and the condition “if > > > (!in_vblank_irq)” will be executed multiple times (we don’t want it). > > > > > > - Inside vkms_crc, the issue is that the returned frame value change for > > > every call of drm_crtc_accurate_vblank_count() because > > > in_vblank_irq == false. > > Hi Ville, > > > OK. So why is it changing? AFAICS it should not change unless the > > timer was moved forward in between the calls. > > Yes Ville, you’re right. We have to update it only when the function > vkms_vblank_simulate() is invoked (timer move forward), and FWIU we do > it when we call drm_crtc_handle_vblank(). However, the current > implementation of vkms, has a call to drm_crtc_accurate_vblank_count() > inside the vkms_vblank_simulate() which is a problem because it also > update the vblank value. FWIU, this patch fixes this issue by taking the > count value in the data struct instead of call > drm_crtc_accurate_vblank_count() which will avoid the extra update. But why does that extra update change the vblank count? -- Ville Syrjälä Intel