On 11/12/2024 15:42, Johan Hovold wrote:
On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote:
+/**
+ * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode
+ * @aux: DisplayPort AUX channel
+ * @enable: Enable or disable transparent mode
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable)
+{
+ u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT :
+ DP_PHY_REPEATER_MODE_NON_TRANSPARENT;
+ int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val);
+
+ return ret == 1 ? 0 : ret;
This looks correct, but I had to go look at drm_dp_dpcd_writeb() to make
sure it never returns 0 (for short transfers).
+}
+EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode);
This appears to be what the driver currently uses, but why not
EXPORT_SYMBOL_GPL?
drivers/gpu/drm/display/drm_dp_helper.c is not GPL licenced, so
this is the right macro to use.
Neil
+
+/**
+ * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard
+ *
+ * @aux: DisplayPort AUX channel
+ * @lttpr_count: Number of LTTPRs
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count)
+{
+ if (!lttpr_count)
+ return 0;
+
+ /*
+ * See DP Standard v2.0 3.6.6.1 about the explicit disabling of
+ * non-transparent mode and the disable->enable non-transparent mode
+ * sequence.
+ */
+ drm_dp_lttpr_set_transparent_mode(aux, true);
Error handling?
+
+ if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux, false))
No need to check lttpr_count again here.
+ return 0;
I'd check for errors instead of success here and do the rollback before
returning -EINVAL.
+
+ /*
+ * Roll-back to tranparent mode if setting non-tranparent mode failed or
+ * the number of LTTPRs is invalid
+ */
+ drm_dp_lttpr_set_transparent_mode(aux, true);
+
+ return -EINVAL;
And return 0 explicitly here.
+}
+EXPORT_SYMBOL(drm_dp_lttpr_init);
In any case this works well and is needed for external display on the
Lenovo ThinkPad T14s, while not breaking the X13s which does not need
it:
Tested-by: Johan Hovold <johan+linaro@xxxxxxxxxx>
Johan
