Add a helper to probe a DP link (read out the supported DPCD revision,
maximum rate, link count and capabilities) as well as power up the DP
link and configure it accordingly.
Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx>
Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
Changes in v4:
- fix a couple of typos in comments as pointed out by Alex Deucher
Changes in v3:
- split into drm_dp_link_power_up() and drm_dp_link_configure()
- do not change sink state for DPCD versions earlier than 1.1
- sleep for 1-2 ms after setting local sink to D0 state
- read and write consecutive registers where possible
- read DPCD revision when link is probed
- remove duplicate kerneldoc
drivers/gpu/drm/drm_dp_helper.c | 94 +++++++++++++++++++++++++++++++++++++++++
include/drm/drm_dp_helper.h | 17 ++++++++
2 files changed, 111 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index b26d46b00b05..eea15b1414ed 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -472,3 +472,97 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
DP_LINK_STATUS_SIZE);
}
EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
+
+/**
+ * drm_dp_link_probe() - probe a DisplayPort link for capabilities
+ * @aux: DisplayPort AUX channel
+ * @link: pointer to structure in which to return link capabilities
+ *
+ * The structure filled in by this function can usually be passed directly
+ * into drm_dp_link_power_up() and drm_dp_link_configure() to power up and
+ * configure the link based on the link's capabilities.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
+{
+ u8 values[3];
+ int err;
+
+ memset(link, 0, sizeof(*link));
+
+ err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values));
+ if (err < 0)
+ return err;
+
+ link->revision = values[0];
+ link->rate = drm_dp_bw_code_to_link_rate(values[1]);
+ link->num_lanes = values[2] & DP_MAX_LANE_COUNT_MASK;
+
+ if (values[2] & DP_ENHANCED_FRAME_CAP)
+ link->capabilities |= DP_LINK_CAP_ENHANCED_FRAMING;
+
+ return 0;
+}
+
+/**
+ * drm_dp_link_power_up() - power up a DisplayPort link
+ * @aux: DisplayPort AUX channel
+ * @link: pointer to a structure containing the link configuration
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link)
+{
+ u8 value;
+ int err;
+
+ /* DP_SET_POWER register is only available on DPCD v1.1 and later */
+ if (link->revision < 0x11)
+ return 0;
+
+ err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
+ if (err < 0)
+ return err;
+
+ value &= ~DP_SET_POWER_MASK;
+ value |= DP_SET_POWER_D0;
+
+ err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
+ if (err < 0)
+ return err;
+
+ /*
+ * According to the DP 1.1 specification, a "Sink Device must exit the
+ * power saving state within 1 ms" (Section 2.5.3.1, Table 5-52, "Sink
+ * Control Field" (register 0x600).
+ */
+ usleep_range(1000, 2000);
+
+ return 0;
+}
+
+/**
+ * drm_dp_link_configure() - configure a DisplayPort link
+ * @aux: DisplayPort AUX channel
+ * @link: pointer to a structure containing the link configuration
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
+{
+ u8 values[2];
+ int err;
+
+ values[0] = drm_dp_link_rate_to_bw_code(link->rate);
+ values[1] = link->num_lanes;
+
+ if (link->capabilities & DP_LINK_CAP_ENHANCED_FRAMING)
+ values[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;
+
+ err = drm_dp_dpcd_write(aux, DP_LINK_BW_SET, values, sizeof(values));
+ if (err < 0)
+ return err;
+
+ return 0;
+}
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 8af695277a84..c7b3c736c40a 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -291,6 +291,7 @@
#define DP_SET_POWER 0x600
# define DP_SET_POWER_D0 0x1
# define DP_SET_POWER_D3 0x2
+# define DP_SET_POWER_MASK 0x3
#define DP_PSR_ERROR_STATUS 0x2006 /* XXX 1.2? */
# define DP_PSR_LINK_CRC_ERROR (1 << 0)
@@ -468,4 +469,20 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux,
int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
u8 status[DP_LINK_STATUS_SIZE]);
+/*
+ * DisplayPort link
+ */
+#define DP_LINK_CAP_ENHANCED_FRAMING (1 << 0)
+
+struct drm_dp_link {
+ unsigned char revision;
+ unsigned int rate;
+ unsigned int num_lanes;
+ unsigned long capabilities;
+};
+
+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_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
+
#endif /* _DRM_DP_HELPER_H_ */
--
1.8.4.2
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