Factor out from drm_dp_dpcd_read() a function to probe a DPCD address
with a 1-byte read access. This will be needed by the next patch doing a
read from an LTTPR address, which must happen without the preceding
wake-up read in drm_dp_dpcd_read().
v2: Add a probe function instead of exporting drm_dp_dpcd_access(). (Jani)
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
---
drivers/gpu/drm/dp/drm_dp.c | 28 +++++++++++++++++++++++++---
include/drm/dp/drm_dp_helper.h | 1 +
2 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c
index 580016a1b9eb7..b58e30132768d 100644
--- a/drivers/gpu/drm/dp/drm_dp.c
+++ b/drivers/gpu/drm/dp/drm_dp.c
@@ -527,6 +527,29 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
return ret;
}
+/**
+ * drm_dp_dpcd_probe() - probe a given DPCD address with a 1-byte read access
+ * @aux: DisplayPort AUX channel (SST)
+ * @offset: address of the register to probe
+ *
+ * Probe the provided DPCD address by reading 1 byte from it. The function can
+ * be used to trigger some side-effect the read access has, like waking up the
+ * sink, without the need for the read-out value.
+ *
+ * Returns 0 if the read access suceeded, or a negative error code on failure.
+ */
+int drm_dp_dpcd_probe(struct drm_dp_aux *aux, unsigned int offset)
+{
+ u8 buffer;
+ int ret;
+
+ ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset, &buffer, 1);
+ WARN_ON(ret == 0);
+
+ return ret < 0 ? ret : 0;
+}
+EXPORT_SYMBOL(drm_dp_dpcd_probe);
+
/**
* drm_dp_dpcd_read() - read a series of bytes from the DPCD
* @aux: DisplayPort AUX channel (SST or MST)
@@ -559,9 +582,8 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
* monitor doesn't power down exactly after the throw away read.
*/
if (!aux->is_remote) {
- ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, DP_DPCD_REV,
- buffer, 1);
- if (ret != 1)
+ ret = drm_dp_dpcd_probe(aux, DP_DPCD_REV);
+ if (ret < 0)
goto out;
}
diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h
index 1eccd97419436..91af98e6617c6 100644
--- a/include/drm/dp/drm_dp_helper.h
+++ b/include/drm/dp/drm_dp_helper.h
@@ -2053,6 +2053,7 @@ struct drm_dp_aux {
bool is_remote;
};
+int drm_dp_dpcd_probe(struct drm_dp_aux *aux, unsigned int offset);
ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
void *buffer, size_t size);
ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
--
2.30.2
