Commit d8bb92e7 authored by Imre Deak's avatar Imre Deak
Browse files

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: default avatarImre Deak <imre.deak@intel.com>
Reviewed-by: default avatarJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220411132539.984647-1-imre.deak@intel.com
parent f1e4c916

drivers/gpu/drm/dp/drm_dp.c

+28 −5
Original line number Diff line number Diff line
@@ -527,6 +527,31 @@ 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);



	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)
@@ -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;

}

include/drm/dp/drm_dp_helper.h

+1 −0
Original line number Diff line number Diff line
@@ -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,