drm/i915: Add retries for LSPCON detection

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

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102294
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102295
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102359
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103186
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1507630064-17908-4-git-send-email-shashank.sharma@intel.com

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;
@@ -140,7 +141,15 @@ static bool lspcon_probe(struct intel_lspcon *lspcon)
 			DRM_LSPCON_MODE_PCON : DRM_LSPCON_MODE_LS;
 
 	/* Lets probe the adaptor and check its type */
+	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)
+			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));