drm/dp: Factor out a function to probe a DPCD address

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().

While at it add tracing for the 1 byte read even if the read was
successful.

v2: Add a probe function instead of exporting drm_dp_dpcd_access(). (Jani)
v3: Add tracing for the 1-byte read even if the read was successful. (Khaled)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Khaled Almahallawy <khaled.almahallawy@intel.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220411132539.984647-1-imre.deak@intel.com

diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c
index 703972a..b76260e 100644 (file)
--- a/drivers/gpu/drm/dp/drm_dp.c
+++ b/drivers/gpu/drm/dp/drm_dp.c
@@ -528,6 +528,31 @@ unlock:
 }
 
 /**
+ * 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);
+
+       drm_dp_dump_access(aux, DP_AUX_NATIVE_READ, offset, &buffer, ret);
+
+       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)
  * @offset: address of the (first) register to read
@@ -559,10 +584,9 @@ 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)
-                       goto out;
+               ret = drm_dp_dpcd_probe(aux, DP_DPCD_REV);
+               if (ret < 0)
+                       return ret;
        }
 
        if (aux->is_remote)
@@ -571,7 +595,6 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
                ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset,
                                         buffer, size);
 
-out:
        drm_dp_dump_access(aux, DP_AUX_NATIVE_READ, offset, buffer, ret);
        return ret;
 }

diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h
index 51e02cf..53d1e72 100644 (file)
--- 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,