Re: [PATCH] drm/i915: dsi: fix pipe-off timeout due to port vs. pipe disable ordering

["Kumar, Shobhit" <shobhit.kumar@intel.com>]

On 5/27/2014 8:42 PM, Imre Deak wrote:
> On Tue, 2014-05-27 at 19:45 +0530, Kumar, Shobhit wrote:
>> On 5/27/2014 6:45 PM, Imre Deak wrote:
>>> If we disable first the port (by disabling DPI) and only then the
>>> display pipe the pipe-off flag will never be set, possibly leading to a
>>> hanged pipe state at the next modeset-enable.
>>>
>>> Note that according to the VLV2 display cluster HAS, we should disable
>>> the port before the pipe. This doesn't seem to match reality based on
>>> the above and it's also asymmetric with the enabling sequence, where we
>>> first enable the port and then the pipe.
>>>
>>> Signed-off-by: Imre Deak <imre.deak@intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/intel_dsi.c | 9 ++++++++-
>>>    1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/intel_dsi.c b/drivers/gpu/drm/i915/intel_dsi.c
>>> index e73bec6..3756af1 100644
>>> --- a/drivers/gpu/drm/i915/intel_dsi.c
>>> +++ b/drivers/gpu/drm/i915/intel_dsi.c
>>> @@ -206,6 +206,11 @@ static void intel_dsi_enable_nop(struct intel_encoder *encoder)
>>>    	 */
>>>    }
>>>
>>> +static void intel_dsi_disable_nop(struct intel_encoder *encoder)
>>> +{
>>> +	DRM_DEBUG_KMS("\n");
>>> +}
>>> +
>>
>> Make this as *_pre_disable and the SHUTDOWN command should be sent in
>> this function. That is the recommended sequence in disable path. First
>> thing is to shutdown the panel. Remove that bit from the intel_dsi_disable.
>
> I tried this, but it results in a "Timeout waiting for DPI FIFO empty"
> error when sending the SHUTDOWN command. This order would be also
> asymmetric with the enabling sequence where we first turn on the panel
> and only then enable the pipe. So I would need more explanation for the
> above before moving the SHUTDOWN command earlier.
>

I think checking DPI FIFO empty before sending DPI commands is wrong. 
Unless pipe is stopped DPI FIFO will not be empty. Basically we should 
test for DPI FIFO full in case of error. I was planning to look into 
that correction.

Regards
Shobhit