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Message-ID: <20150119090847.GQ10649@intel.com> Date: Mon, 19 Jan 2015 11:08:47 +0200 From: Ville Syrjälä <ville.syrjala@...ux.intel.com> To: Jeremiah Mahler <jmmahler@...il.com>, Matt Roper <matthew.d.roper@...el.com>, Daniel Vetter <daniel.vetter@...el.com>, Jani Nikula <jani.nikula@...ux.intel.com>, David Airlie <airlied@...ux.ie>, Alex Deucher <alexander.deucher@....com>, Dave Airlie <airlied@...hat.com>, Ander Conselvan de Oliveira <conselvan2@...il.com>, linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org Subject: Re: [Intel-gfx] [BUG, bisect] drm/i915: mouse pointer lags and overshoots On Sat, Jan 17, 2015 at 02:06:35AM -0800, Jeremiah Mahler wrote: > Matt, all, > > Commit ea2c67bb4aff introduces a bug which causes the mouse to move in a > very unusual way, as if it has a lot of inertia. It will lag behind and > then overshoot the expected position. > > I reproduced this bug on all my machines which use the drm/i915 drivers > and it affects all forms of mouse pointers including both touchpads and > usb mice. The patch is present in linux-next 20150116. > > commit ea2c67bb4affa84080c616920f3899f123786e56 > Author: Matt Roper <matthew.d.roper@...el.com> > Date: Tue Dec 23 10:41:52 2014 -0800 > > drm/i915: Move to atomic plane helpers (v9) I guess this is caused by the atomic code refusing to update the plane more than once per vrefresh. So we need to allow the fps>vrefresh rate case to remove the regression. The old cursor code had basically a gross hack to allow this. It just unpinned the old fb before the display engine was done with it, and _after_ unpinning it flipped to the new buffer (with the obvious extra delay of the flip happening on the next vblank). So there was no guarantee the old buffer was still around (or had the correct content) while the display engine was still scanning it out. So to fix this properly we need a vblank worker of some sort. The other issues we nee to know which fb is being scanned out at which point to unpin the correct old buffer. For that we can use the hardware frame counter. We could use some other mechanims too (SURFLIVE, flip counter etc.) but the frame counter is the most ubiqitious method we have. The one extra problem is gen2 doesn't have even the frame counter, so some extra care would be needed there. I'm thinking for gen2 we might allow the driver to call into the vblank core code to update the cooked counter at any time based on the scanline counter and monotonic timestamp. That combined with the vblank evade mechanism should make reasonably sure we have an up to date notion of which frame is currently getting scanned out. We need the extra call into the vblank core since just after the vblank start, the vblank interrupt handler may not have executed yet (especially since gen2 vblank irq fires actually at the frame start which is a delayed version of the vblank start, even though the flip happes at vblank start). So we need an explicit call to make sure the cooked counter is already updated before the irq handler has executed. I have some changes lined up for the vblank code which I think could help make sure he extra call won't increment the counter spuriously, but I have to clean those up a bit before sending them out. -- Ville Syrjälä Intel OTC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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