[PATCH v2 2/7] drm: Read DPCD receiver capability for DP to VGA converter

[Mika Kahola]

Read from DPCD receiver capability field the max allowed
pixel clock and bits per component for DP to VGA converter.

Signed-off-by: Mika Kahola <mika.kahola at intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c  | 46 ++++++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_drv.h |  2 ++
 include/drm/drm_dp_helper.h      | 21 ++++++++++++++++++
 3 files changed, 69 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index eeaf5a7..c5bec6f 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -412,6 +412,52 @@ int drm_dp_link_power_down(struct drm_dp_aux *aux, struct drm_dp_link *link)
 }
 EXPORT_SYMBOL(drm_dp_link_power_down);
 
+/*
+ * drm_dp_bd() - read DisplayPort Receiver Capability Fields for
+ * DP branch devices
+ * @aux: DisplayPort AUX channel
+ * @bd: pointer to a structure containing DP branch device information
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_bd(struct drm_dp_aux *aux, struct drm_dp_bd *bd)
+{
+	uint8_t info[4];
+	uint8_t dfp;
+	bool detailed_cap_info;
+	int err, size;
+
+	err = drm_dp_dpcd_read(aux, DP_DOWNSTREAMPORT_PRESENT, &dfp, sizeof(dfp));
+	if (err < 0)
+		return err;
+
+	bd->present = dfp & 0x1;
+
+	if (!bd->present)
+		return 0;
+
+	detailed_cap_info = dfp & DP_DETAILED_CAP_INFO_AVAILABLE;
+
+	size = detailed_cap_info ? 4 : 1;
+
+	err = drm_dp_dpcd_read(aux, DP_DOWNSTREAM_PORT_0, info, size);
+	if (err < 0)
+		return err;
+
+	bd->type = info[0] & DP_DS_PORT_TYPE_MASK;
+	bd->hpd = info[0] & DP_DS_PORT_HPD;
+
+	if (detailed_cap_info) {
+		if (bd->type & DP_DS_PORT_TYPE_VGA) {
+			bd->dfp.vga.dot_clk = info[1] * 8 * 1000;
+			bd->dfp.vga.bpc = info[2] & DP_DS_VGA_MAX_BPC_MASK;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_bd);
+
 /**
  * drm_dp_link_configure() - configure a DisplayPort link
  * @aux: DisplayPort AUX channel
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 94a44af..7d2d93f 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -866,6 +866,8 @@ struct intel_dp {
 
 	bool train_set_valid;
 
+	struct drm_dp_bd bd;
+
 	/* Displayport compliance testing */
 	unsigned long compliance_test_type;
 	unsigned long compliance_test_data;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 4049af9..fe6cfdc 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -801,10 +801,31 @@ struct drm_dp_link {
 	unsigned long capabilities;
 };
 
+/*
+ * DP to VGA
+ */
+struct drm_dp_vga {
+	int dot_clk;
+	uint8_t bpc;
+};
+
+/*
+ * Branch device
+ */
+struct drm_dp_bd {
+	bool present;
+	int type;
+	bool hpd;
+	union {
+		struct drm_dp_vga vga;
+	} dfp;
+};
+
 int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link);
 int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);
 int drm_dp_link_power_down(struct drm_dp_aux *aux, struct drm_dp_link *link);
 int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
+int drm_dp_bd(struct drm_dp_aux *aux, struct drm_dp_bd *bd);
 
 int drm_dp_aux_register(struct drm_dp_aux *aux);
 void drm_dp_aux_unregister(struct drm_dp_aux *aux);
-- 
1.9.1