drm/i915: Restore GMBUS operation after a failed bit-banging fallback
When the GMBUS based i2c transfer times out, we try to fall back to
bit-banging and retry the operation that way. However if the bit-banging
attempt also fails, we should probably go back to the GMBUS method for
the next attempt. Maybe there simply wasn't anyone one the bus at this
time.
There's also a bit of a mess going on with the force_bit handling.
It's supposed to be a ref count actually, and it is as far as
intel_gmbus_force_bit() is concerned. But it's treated as just a
flag by the timeout based bit-banging fallback. I suppose that's
fine since we should never end up in the timeout fallback case
if force_bit was already non-zero. However now that we want to restore
things back to where they were after the bit-banging attempt failed,
we're going to have to do things a bit differently to avoid clobbering
the force_bit count as set up by intel_gmbus_force_bit(). So let's
dedicate the high bit as a flag for the low level timeout based fallback
and treat the rest of the bits as a ref count just as before.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1457366220-29409-4-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index a9c8211..6c45adb 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -996,6 +996,7 @@
struct intel_gmbus {
struct i2c_adapter adapter;
+#define GMBUS_FORCE_BIT_RETRY (1U << 31)
u32 force_bit;
u32 reg0;
i915_reg_t gpio_reg;