[Intel-gfx] [PATCH v3 3/3] drm/i915: Add retries for LSPCON detection

[Imre Deak]

On Tue, Oct 10, 2017 at 03:37:44PM +0530, Shashank Sharma wrote:
> We read the dp dual mode Adapter identifier to detect the
> LSPCON device. It's been observed from the CI testing that in
> few cases, this read can get delayed or fail. For such scenarios,
> LSPCON vendors suggest to retry the read operation.
> 
> This patch adds retry in the probe function, while reading
> LSPCON identifier.
> 
> V3: added this patch in the series
> 
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: Imre Deak <imre.deak at intel.com>
> Signed-off-by: Shashank Sharma <shashank.sharma at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_lspcon.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lspcon.c b/drivers/gpu/drm/i915/intel_lspcon.c
> index 7688254..dcbc786 100644
> --- a/drivers/gpu/drm/i915/intel_lspcon.c
> +++ b/drivers/gpu/drm/i915/intel_lspcon.c
> @@ -132,6 +132,7 @@ static bool lspcon_wake_native_aux_ch(struct intel_lspcon *lspcon)
>  
>  static bool lspcon_probe(struct intel_lspcon *lspcon)
>  {
> +	int retry;
>  	enum drm_dp_dual_mode_type adaptor_type;
>  	struct i2c_adapter *adapter = &lspcon_to_intel_dp(lspcon)->aux.ddc;
>  	enum drm_lspcon_mode expected_mode;
> @@ -140,10 +141,18 @@ static bool lspcon_probe(struct intel_lspcon *lspcon)
>  			DRM_LSPCON_MODE_PCON : DRM_LSPCON_MODE_LS;
>  
>  	/* Lets probe the adaptor and check its type */
> -	adaptor_type = drm_dp_dual_mode_detect(adapter);
> +	for (retry = 0; retry < 6; retry++) {
> +		if (retry)
> +			usleep_range(500, 1000);
> +
> +		adaptor_type = drm_dp_dual_mode_detect(adapter);
> +		if (adaptor_type == DRM_DP_DUAL_MODE_LSPCON)

I wondered if this should be (adaptor_type != DRM_DP_DUAL_MODE_UNKNOWN),
since the other cases are not known to cause a problem. But we'll probe
LSPCON only if VBT says so and if VBT is broken we'll anyway incur the
retry overhead here. So looks ok:

Reviewed-by: Imre Deak <imre.deak at intel.com>

> +			break;
> +	}
> +
>  	if (adaptor_type != DRM_DP_DUAL_MODE_LSPCON) {
>  		DRM_DEBUG_KMS("No LSPCON detected, found %s\n",
> -			drm_dp_get_dual_mode_type_name(adaptor_type));
> +			       drm_dp_get_dual_mode_type_name(adaptor_type));
>  		return false;
>  	}
>  
> -- 
> 2.7.4
>