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Subject[PATCH 5/9] drm/bridge: ti-sn65dsi86: Read num lanes from the DP sink
Date
At least one panel hooked up to the bridge (AUO B116XAK01) only
supports 1 lane of DP. Let's read this information and stop
hardcoding 4 DP lanes.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

drivers/gpu/drm/bridge/ti-sn65dsi86.c | 32 +++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index d55d19759796..0fc9e97b2d98 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -313,8 +313,7 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge)
goto err_dsi_host;
}

- /* TODO: setting to 4 lanes always for now */
- pdata->dp_lanes = 4;
+ /* TODO: setting to 4 MIPI lanes always for now */
dsi->lanes = 4;
dsi->format = MIPI_DSI_FMT_RGB888;
dsi->mode_flags = MIPI_DSI_MODE_VIDEO;
@@ -511,12 +510,41 @@ static void ti_sn_bridge_set_video_timings(struct ti_sn_bridge *pdata)
usleep_range(10000, 10500); /* 10ms delay recommended by spec */
}

+static unsigned int ti_sn_get_max_lanes(struct ti_sn_bridge *pdata)
+{
+ u8 data;
+ int ret;
+
+ ret = drm_dp_dpcd_readb(&pdata->aux, DP_MAX_LANE_COUNT, &data);
+ if (ret != 1) {
+ DRM_DEV_ERROR(pdata->dev,
+ "Can't read lane count (%d); assuming 4\n", ret);
+ return 4;
+ }
+
+ return data & DP_LANE_COUNT_MASK;
+}
+
static void ti_sn_bridge_enable(struct drm_bridge *bridge)
{
struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge);
unsigned int val;
int ret;

+ /*
+ * Run with the maximum number of lanes that the DP sink supports.
+ *
+ * Depending use cases, we might want to revisit this later because:
+ * - It's plausible that someone may have run fewer lines to the
+ * sink than the sink actually supports, assuming that the lines
+ * will just be driven at a higher rate.
+ * - The DP spec seems to indicate that it's more important to minimize
+ * the number of lanes than the link rate.
+ *
+ * If we do revisit, it would be important to measure the power impact.
+ */
+ pdata->dp_lanes = ti_sn_get_max_lanes(pdata);
+
/* DSI_A lane config */
val = CHA_DSI_LANES(4 - pdata->dsi->lanes);
regmap_update_bits(pdata->regmap, SN_DSI_LANES_REG,
--
2.24.1.735.g03f4e72817-goog
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