From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Roper Subject: Re: [PATCH v2] drm/i915: fix screen flickering Date: Thu, 14 May 2015 07:28:36 -0700 Message-ID: <20150514142836.GE25648@intel.com> References: <20150514032118.GD25648@intel.com> <1431587799-5399-1-git-send-email-t.gummerer@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <1431587799-5399-1-git-send-email-t.gummerer@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" To: Thomas Gummerer Cc: David Airlie , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Daniel Vetter List-Id: dri-devel@lists.freedesktop.org T24gVGh1LCBNYXkgMTQsIDIwMTUgYXQgMDk6MTY6MzlBTSArMDIwMCwgVGhvbWFzIEd1bW1lcmVy IHdyb3RlOgo+IENvbW1pdCBjOWYwMzhhMWE1OTIgKCJkcm0vaTkxNTogRG9uJ3QgYXNzdW1lIHBy 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Nikula , Daniel Vetter , jan@gondor.com, Tvrtko Ursulin , Michael Leuchtenburg Subject: Re: [PATCH v2] drm/i915: fix screen flickering Message-ID: <20150514142836.GE25648@intel.com> References: <20150514032118.GD25648@intel.com> <1431587799-5399-1-git-send-email-t.gummerer@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1431587799-5399-1-git-send-email-t.gummerer@gmail.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 14, 2015 at 09:16:39AM +0200, Thomas Gummerer wrote: > Commit c9f038a1a592 ("drm/i915: Don't assume primary & cursor are > always on for wm calculation (v4)") fixes a null pointer dereference. > Setting the primary and cursor panes to false in > ilk_compute_wm_parameters to false does however give the following > errors in the kernel log and causes the screen to flicker. > > [ 101.133716] [drm:intel_set_cpu_fifo_underrun_reporting [i915]] > *ERROR* uncleared fifo underrun on pipe A > [ 101.133725] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] > *ERROR* CPU pipe A FIFO underrun > > Always setting the panes to enabled fixes this error. > > Helped-by: Matt Roper > Signed-off-by: Thomas Gummerer Seems like a reasonable short-term workaround and returns us to how the code used to behaves. Reviewed-by: Matt Roper > --- > > > Sorry, I missed your patch when you first sent it. That type of fix > > looks like an okay workaround while we do a more in-depth rework of the > > watermark system. However I think your patch could cause a crash if we > > disable the primary plane via the universal plane interface; if we do > > that, p->pri.bytes_per_pixel is set to 0, but since we're now pretending > > the primary plane is always enabled, ilk_wm_fbc() can eventually get > > called and use that 0 in the denominator of a division operation. > > > > If you just squash the following change into your patch, I think it should be > > safe: > > [...] > > Thank you very much for the suggestion, here is an updated version of the > patch. > > drivers/gpu/drm/i915/intel_pm.c | 24 +++++++++++------------- > 1 file changed, 11 insertions(+), 13 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c > index fa4ccb3..555b896 100644 > --- a/drivers/gpu/drm/i915/intel_pm.c > +++ b/drivers/gpu/drm/i915/intel_pm.c > @@ -2045,22 +2045,20 @@ static void ilk_compute_wm_parameters(struct drm_crtc *crtc, > p->pipe_htotal = intel_crtc->config->base.adjusted_mode.crtc_htotal; > p->pixel_rate = ilk_pipe_pixel_rate(dev, crtc); > > - if (crtc->primary->state->fb) { > - p->pri.enabled = true; > + if (crtc->primary->state->fb) > p->pri.bytes_per_pixel = > crtc->primary->state->fb->bits_per_pixel / 8; > - } else { > - p->pri.enabled = false; > - p->pri.bytes_per_pixel = 0; > - } > + else > + p->pri.bytes_per_pixel = 4; > + > + p->cur.bytes_per_pixel = 4; > + /* > + * TODO: for now, assume primary and cursor planes are always enabled. > + * Setting them to false makes the screen flicker. > + */ > + p->pri.enabled = true; > + p->cur.enabled = true; > > - if (crtc->cursor->state->fb) { > - p->cur.enabled = true; > - p->cur.bytes_per_pixel = 4; > - } else { > - p->cur.enabled = false; > - p->cur.bytes_per_pixel = 0; > - } > p->pri.horiz_pixels = intel_crtc->config->pipe_src_w; > p->cur.horiz_pixels = intel_crtc->base.cursor->state->crtc_w; > > -- > 2.4.0.184.g8e1974e > -- Matt Roper Graphics Software Engineer IoTG Platform Enabling & Development Intel Corporation (916) 356-2795