[PATCH 16/20] drm: add function to read vendor OUI

[Shashank Sharma <shashank.sharma@xxxxxxxxx>]

This patch adds a helper function in DP dual mode layer to
read the vendor's IEEE OUI signature from a Dual mode adapter.
This will be used to differentiate between different LSPCON
vendors, to address their custom programming requirements.

Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: Imre Deak <imre.deak@xxxxxxxxx>
Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxxxx>
---
 drivers/gpu/drm/drm_dp_dual_mode_helper.c | 24 ++++++++++++++++++++++++
 include/drm/drm_dp_dual_mode_helper.h     |  4 +++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
index 80e62f6..0b890dc 100644
--- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -396,6 +396,30 @@ const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type)
 EXPORT_SYMBOL(drm_dp_get_dual_mode_type_name);
 
 /**
+ * drm_lspcon_get_vendor_oui: match vendor OUI signature
+ * @adapter: i2c adapter under action
+ * @vendor_id = 3 bytes of vendor OUI signature, LSB=lower byte
+ *
+ * Returns:
+ * Vendor OUI id if got one, 0 if not
+ */
+uint32_t drm_lspcon_get_vendor_oui(struct i2c_adapter *adapter)
+{
+	uint8_t sign[3] = {0, };
+	uint32_t oui = 0;
+
+	if (drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_LSPCON_OUI_OFFSET,
+						sign, 3)) {
+		DRM_ERROR("Can't identify vendor sign\n");
+		return 0;
+	}
+
+	oui = (sign[0] << 16) | (sign[1] << 8) | sign[2];
+	return oui;
+}
+EXPORT_SYMBOL(drm_lspcon_get_vendor_oui);
+
+/**
  * drm_lspcon_get_mode: Get LSPCON's current mode of operation by
  * reading offset (0x80, 0x41)
  * @adapter: I2C-over-aux adapter
diff --git a/include/drm/drm_dp_dual_mode_helper.h b/include/drm/drm_dp_dual_mode_helper.h
index 4c42db8..f81b526 100644
--- a/include/drm/drm_dp_dual_mode_helper.h
+++ b/include/drm/drm_dp_dual_mode_helper.h
@@ -60,7 +60,8 @@
 /* LSPCON specific registers, defined by MCA */
 #define DP_DUAL_MODE_LSPCON_MODE_CHANGE		0x40
 #define DP_DUAL_MODE_LSPCON_CURRENT_MODE		0x41
-#define  DP_DUAL_MODE_LSPCON_MODE_PCON			0x1
+#define DP_DUAL_MODE_LSPCON_MODE_PCON			0x1
+#define DP_DUAL_MODE_LSPCON_OUI_OFFSET			0x11
 
 struct i2c_adapter;
 
@@ -116,4 +117,5 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
 			enum drm_lspcon_mode *current_mode);
 int drm_lspcon_set_mode(struct i2c_adapter *adapter,
 			enum drm_lspcon_mode reqd_mode);
+uint32_t drm_lspcon_get_vendor_oui(struct i2c_adapter *adapter);
 #endif
-- 
2.7.4

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