[PATCH v3 07/12] drm: Compute max pixel rate for DP sink

[Mika Kahola <mika.kahola@xxxxxxxxx>]

For DP branch devices DPCD register may define the max supported
pixel rate for VGA dongles. This patch adds a check if DPCD register
value is less than current setting for pixel rate.

Signed-off-by: Mika Kahola <mika.kahola@xxxxxxxxx>
---
 drivers/gpu/drm/drm_dp_helper.c | 22 ++++++++++++++++++++++
 include/drm/drm_dp_helper.h     |  1 +
 2 files changed, 23 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 2c91771..b222aa0 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -413,6 +413,28 @@ 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_max_sink_dotclock() - Compute max pixel rate
+ * @dotclk: reference pixel rate
+ * @bd: pointer to a structure containing DP branch device information
+ *
+ * Returns max supported pixel rate.
+ */
+int drm_dp_max_sink_dotclock(int dotclk, struct drm_dp_bd *bd)
+{
+	int max_dotclk = dotclk;
+
+	/* DP to VGA dongle may define max pixel rate in DPCD */
+	if (bd->present) {
+		if ((bd->type & DP_DS_PORT_TYPE_VGA) &&
+		    (bd->dfp.vga.dot_clk > 0))
+			max_dotclk = min(dotclk, bd->dfp.vga.dot_clk);
+	}
+
+	return max_dotclk;
+}
+EXPORT_SYMBOL(drm_dp_max_sink_dotclock);
+
+/*
  * drm_dp_bd() - read DisplayPort Receiver Capability Fields for
  * DP branch devices
  * @aux: DisplayPort AUX channel
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 831f944..ee4084d 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -882,6 +882,7 @@ 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_max_sink_dotclock(int dotclk, struct drm_dp_bd *bd);
 int drm_dp_bd(struct drm_dp_aux *aux, struct drm_dp_bd *bd);
 
 int drm_dp_aux_register(struct drm_dp_aux *aux);
-- 
1.9.1

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