[PATCH v4 09/11] drm/i915: Check pixel rate for DP to VGA dongle

[Mika Kahola]

Filter out a mode that exceeds the max pixel rate setting
for DP to VGA dongle. This is defined in DPCD register 0x81
if detailed cap info i.e. info field is 4 bytes long and
it is available for DP downstream port.

The register defines the pixel rate divided by 8 in MP/s.

v2: DPCD read outs and computation moved to drm (Ville, Daniel)
v3: Sink pixel rate computation moved to drm_dp_max_sink_dotclock()
    function (Daniel)
v4: Use of drm_dp_helper.c routines to compute max pixel clock (Ville)

Signed-off-by: Mika Kahola <mika.kahola at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 096acbf0..1b94347 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -200,6 +200,23 @@ intel_dp_mode_valid(struct drm_connector *connector,
 	int target_clock = mode->clock;
 	int max_rate, mode_rate, max_lanes, max_link_clock;
 	int max_dotclk = to_i915(connector->dev)->max_dotclk_freq;
+	bool is_branch_device;
+	int max_dp_clk;
+	int type;
+	uint8_t port_cap[4];
+
+	is_branch_device = intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
+		DP_DWN_STRM_PORT_PRESENT;
+
+	if (is_branch_device) {
+		drm_dp_downstream_port_cap(&intel_dp->aux, intel_dp->dpcd, port_cap);
+		type = drm_dp_downstream_type(intel_dp->dpcd, port_cap);
+		max_dp_clk = drm_dp_downstream_max_clock(intel_dp->dpcd, port_cap);
+
+		if ((type == DP_DS_PORT_TYPE_VGA) && (max_dp_clk > 0)) {
+			max_dotclk = min(max_dotclk, max_dp_clk);
+		}
+	}
 
 	if (is_edp(intel_dp) && fixed_mode) {
 		if (mode->hdisplay > fixed_mode->hdisplay)
-- 
1.9.1