Hi Daniel Vetter,
I'm working on touch devices Chromium OS, and I've noticed a regression between 3.8 and 3.9-rc1, which was posted yesterday.
The hardware in question is a Chromebook Pixel. For this device, we have i2c input devices: atmel mxt224s touchpad and atmel mxt1664s touchscreen. The touchpad is on bus 1, "i915 gmbus vga" at 1-004b. The touchscreen is on bus 2, "i915 gmbus panel" at 2-004a.
I was testing v3.9-rc1 on the Pixel and the touchscreen driver is being returned -110 (-ETIMEDOUT) on an i2c_transfer after several seconds of both touch devices working correctly. At the time of the failure, there are no error messages from GMBUS that I can see, but the bus never recovers. I can keep interacting with the touchscreen or touchpad, and the interrupts trigger reads, but all subsequent reads return -110.
I noticed that between 3.8 and 3.9-rc1, your patch series to add gmbus irq support was merged. After bisecting, I found that this commit seems to be causing the timeout problem. Reverting it makes the problem go away, and the bus is stable.
commit 2c438c0273b76d6cb158f8bdd0aa3ebf66e48a28 Author: Daniel Vetter daniel.vetter@ffwll.ch Date: Sat Dec 1 13:53:46 2012 +0100
drm/i915: use gmbus irq to wait for gmbus idle
GMBUS_ACTIVE has inverted sense and so doesn't fit into the wait_hw_status helper, hence create a new gmbus_wait_idle functions. Also, we only care about the idle irq event and nothing else, which allows us to use the wait_event_timeout helper directly without jumping through hoops to catch NAKs.
Since gen2/3 don't have gmbus interrupts, handle them separately with the old wait_for macro.
This shaves another few ms off reading EDID from a hdmi screen on my testbox here. EDID reading with interrupt driven gmbus is now as fast as with busy-looping gmbus at 28 ms here (with negligible cpu overhead).
Reviewed-by: Imre Deak imre.deak@intel.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch
Is there anything I can do to help debug this some more?
-- Benson Leung Software Engineer, Chrom* OS bleung@chromium.org