[PATCH v2] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

[PATCH v2] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

[jim.bride]

From: Jim Bride <jim.bride@linux.intel.com>

According to the HSW b-spec we need to try clock divisors of 63
and 72, each 3 or more times, when attempting DP AUX channel
communication on a server chipset.  This actually wasn't happening
due to a short-circuit that only checked the DP_AUX_CH_CTL_DONE bit
in status rather than checking that the operation was done and
that DP_AUX_CH_CTL_TIME_OUT_ERROR was not set.

[v2] Implemented alternate solution suggested by Jani Nikula.

Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 0edc305..7d1e024 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -893,10 +893,8 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 				continue;
 			}
 			if (status & DP_AUX_CH_CTL_DONE)
-				break;
+				goto done;
 		}
-		if (status & DP_AUX_CH_CTL_DONE)
-			break;
 	}
 
 	if ((status & DP_AUX_CH_CTL_DONE) == 0) {
@@ -905,6 +903,7 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 		goto out;
 	}
 
+done:
 	/* Check for timeout or receive error.
 	 * Timeouts occur when the sink is not connected
 	 */
-- 
1.9.1

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Re: [PATCH v2] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

[Jani Nikula]

On Wed, 27 May 2015, jim.bride@linux.intel.com wrote:
> From: Jim Bride <jim.bride@linux.intel.com>
>
> According to the HSW b-spec we need to try clock divisors of 63
> and 72, each 3 or more times, when attempting DP AUX channel
> communication on a server chipset.  This actually wasn't happening
> due to a short-circuit that only checked the DP_AUX_CH_CTL_DONE bit
> in status rather than checking that the operation was done and
> that DP_AUX_CH_CTL_TIME_OUT_ERROR was not set.
>
> [v2] Implemented alternate solution suggested by Jani Nikula.
>
> Signed-off-by: Jim Bride <jim.bride@linux.intel.com>

Cc: stable@vger.kernel.org
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/intel_dp.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 0edc305..7d1e024 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -893,10 +893,8 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
>  				continue;
>  			}
>  			if (status & DP_AUX_CH_CTL_DONE)
> -				break;
> +				goto done;
>  		}
> -		if (status & DP_AUX_CH_CTL_DONE)
> -			break;
>  	}
>  
>  	if ((status & DP_AUX_CH_CTL_DONE) == 0) {
> @@ -905,6 +903,7 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
>  		goto out;
>  	}
>  
> +done:
>  	/* Check for timeout or receive error.
>  	 * Timeouts occur when the sink is not connected
>  	 */
> -- 
> 1.9.1
>

-- 
Jani Nikula, Intel Open Source Technology Center
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Re: [PATCH v2] drm/i915/hsw: Fix workaround for server AUX channel clock divisor

[Jani Nikula]

On Thu, 28 May 2015, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> On Wed, 27 May 2015, jim.bride@linux.intel.com wrote:
>> From: Jim Bride <jim.bride@linux.intel.com>
>>
>> According to the HSW b-spec we need to try clock divisors of 63
>> and 72, each 3 or more times, when attempting DP AUX channel
>> communication on a server chipset.  This actually wasn't happening
>> due to a short-circuit that only checked the DP_AUX_CH_CTL_DONE bit
>> in status rather than checking that the operation was done and
>> that DP_AUX_CH_CTL_TIME_OUT_ERROR was not set.
>>
>> [v2] Implemented alternate solution suggested by Jani Nikula.
>>
>> Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
>
> Cc: stable@vger.kernel.org
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>

...and pushed to drm-intel-fixes, thanks for the patch.

BR,
Jani.

>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 0edc305..7d1e024 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -893,10 +893,8 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
>>  				continue;
>>  			}
>>  			if (status & DP_AUX_CH_CTL_DONE)
>> -				break;
>> +				goto done;
>>  		}
>> -		if (status & DP_AUX_CH_CTL_DONE)
>> -			break;
>>  	}
>>  
>>  	if ((status & DP_AUX_CH_CTL_DONE) == 0) {
>> @@ -905,6 +903,7 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
>>  		goto out;
>>  	}
>>  
>> +done:
>>  	/* Check for timeout or receive error.
>>  	 * Timeouts occur when the sink is not connected
>>  	 */
>> -- 
>> 1.9.1
>>
>
> -- 
> Jani Nikula, Intel Open Source Technology Center

-- 
Jani Nikula, Intel Open Source Technology Center
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