[PATCH 3/4] drm/i915: Restore GMBUS operation after a failed bit-banging fallback

ville.syrjala
2016-03-07T15:57:14Z

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

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>
---
drivers/gpu/drm/i915/i915_drv.h | 1 +
drivers/gpu/drm/i915/intel_i2c.c | 10 +++++++---
2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index f37ac120a29d..2348fea59592 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1043,6 +1043,7 @@ struct intel_fbc_work;

struct intel_gmbus {
struct i2c_adapter adapter;
+#define GMBUS_FORCE_BIT_RETRY (1U << 31)
u32 force_bit;
u32 reg0;
i915_reg_t gpio_reg;
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 7bf8a485e18f..5d4b3604afd2 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -579,7 +579,6 @@ timeout:
* Hardware may not support GMBUS over these pins? Try GPIO bitbanging
* instead. Use EAGAIN to have i2c core retry.
*/
- bus->force_bit = 1;
ret = -EAGAIN;

out:
@@ -597,10 +596,15 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
mutex_lock(&dev_priv->gmbus_mutex);

- if (bus->force_bit)
+ if (bus->force_bit) {
ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
- else
+ if (ret < 0)
+ bus->force_bit &= ~GMBUS_FORCE_BIT_RETRY;
+ } else {
ret = do_gmbus_xfer(adapter, msgs, num);
+ if (ret == -EAGAIN)
+ bus->force_bit |= GMBUS_FORCE_BIT_RETRY;
+ }

mutex_unlock(&dev_priv->gmbus_mutex);
intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
--
2.4.10