GMBUS should hopefully actually work now in most cases. So, report any timeout conditions using DRM_ERROR(), especially for the case where the timeout causes fallback to bit-bang mode.
From observations, the GMBUS transfers timeout and switch to Bit-Banging
when the corresponding pins are not actually hooked up to anything. In these cases, there is no NAK, nor timeout, nor any other indication from the GMBUS controller that a transaction fails. The first gmbus transaction timeout is caught by the "wait_for" timeout, causing the transition to bit-banging mode for subsequent (failed) attempts.
This might be what was meant by the following note in the GPIO_CTL description: "The registers that control digital display (HDMI/DVI, DisplayPort) pins should only be utilized if the Port Detected bit in the related control register is set to 1." (http://intellinuxgraphics.org/documentation/SNB/IHD_OS_Vol3_Part3.pdf, section 2.2.2)
Signed-off-by: Daniel Kurtz djkurtz@chromium.org --- drivers/gpu/drm/i915/intel_i2c.c | 10 +++++----- 1 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c index 73431ed..154fedd 100644 --- a/drivers/gpu/drm/i915/intel_i2c.c +++ b/drivers/gpu/drm/i915/intel_i2c.c @@ -380,8 +380,8 @@ gmbus_xfer(struct i2c_adapter *adapter, */ if (wait_for((I915_READ(GMBUS2 + reg_offset) & GMBUS_ACTIVE) == 0, 10)) { - DRM_INFO("GMBUS [%s] timed out waiting for idle\n", - adapter->name); + DRM_ERROR("GMBUS [%s] timed out waiting for idle\n", + adapter->name); ret = -ETIMEDOUT; } I915_WRITE(GMBUS0 + reg_offset, 0); @@ -396,7 +396,7 @@ clear_err: */ if (wait_for((I915_READ(GMBUS2 + reg_offset) & GMBUS_ACTIVE) == 0, 10)) - DRM_INFO("GMBUS [%s] timed out after NAK\n", adapter->name); + DRM_ERROR("GMBUS [%s] timed out after NAK\n", adapter->name);
/* Toggle the Software Clear Interrupt bit. This has the effect * of resetting the GMBUS controller and so clearing the @@ -421,8 +421,8 @@ clear_err: goto out;
timeout: - DRM_INFO("GMBUS [%s] timed out, falling back to bit banging on pin %d\n", - bus->adapter.name, bus->reg0 & 0xff); + DRM_ERROR("GMBUS [%s] timed out, falling back to bit banging on pin %d\n", + bus->adapter.name, bus->reg0 & 0xff); I915_WRITE(GMBUS0 + reg_offset, 0);
/* Hardware may not support GMBUS over these pins? Try GPIO bitbanging instead. */