From: Thierry Reding treding@nvidia.com
This is a superset of the current i2c_dp_aux bus functionality and can be used to transfer native AUX in addition to I2C-over-AUX messages.
Helpers are provided to read and write the DPCD, either blockwise or byte-wise. Many of the existing helpers for DisplayPort take a copy of a portion of the DPCD and operate on that, without a way to write data back to the DPCD (e.g. for configuration of the link).
Subsequent patches will build upon this infrastructure to provide common functionality in a generic way.
Reviewed-by: Alex Deucher alexander.deucher@amd.com Reviewed-by: Jani Nikula jani.nikula@intel.com Signed-off-by: Thierry Reding treding@nvidia.com --- Changes in v5: - move comments partially to struct drm_dp_aux_msg in header file - return -EPROTO on short reads in DPCD helpers
Changes in v4: - fix a typo in a comment
Changes in v3: - reorder drm_dp_dpcd_writeb() arguments to be more intuitive - return number of bytes transferred in drm_dp_dpcd_write() - factor out drm_dp_dpcd_access() - describe error codes
drivers/gpu/drm/drm_dp_helper.c | 110 ++++++++++++++++++++++++++++++++++++++++ include/drm/drm_dp_helper.h | 79 +++++++++++++++++++++++++++++ 2 files changed, 189 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 9e978aae8972..da6bcfe178a6 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -346,3 +346,113 @@ int drm_dp_bw_code_to_link_rate(u8 link_bw) } } EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate); + +/** + * DOC: dp helpers + * + * The DisplayPort AUX channel is an abstraction to allow generic, driver- + * independent access to AUX functionality. Drivers can take advantage of + * this by filling in the fields of the drm_dp_aux structure. + * + * Transactions are described using a hardware-independent drm_dp_aux_msg + * structure, which is passed into a driver's .transfer() implementation. + * Both native and I2C-over-AUX transactions are supported. + * + * An AUX channel can also be used to transport I2C messages to a sink. A + * typical application of that is to access an EDID that's present in the + * sink device. The .transfer() function can also be used to execute such + * transactions. The drm_dp_aux_register_i2c_bus() function registers an + * I2C adapter that can be passed to drm_probe_ddc(). Upon removal, drivers + * should call drm_dp_aux_unregister_i2c_bus() to remove the I2C adapter. + */ + +static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request, + unsigned int offset, void *buffer, size_t size) +{ + struct drm_dp_aux_msg msg; + unsigned int retry; + int err; + + memset(&msg, 0, sizeof(msg)); + msg.address = offset; + msg.request = request; + msg.buffer = buffer; + msg.size = size; + + /* + * The specification doesn't give any recommendation on how often to + * retry native transactions, so retry 7 times like for I2C-over-AUX + * transactions. + */ + for (retry = 0; retry < 7; retry++) { + err = aux->transfer(aux, &msg); + if (err < 0) { + if (err == -EBUSY) + continue; + + return err; + } + + if (err < size) + return -EPROTO; + + switch (msg.reply & DP_AUX_NATIVE_REPLY_MASK) { + case DP_AUX_NATIVE_REPLY_ACK: + return err; + + case DP_AUX_NATIVE_REPLY_NACK: + return -EIO; + + case DP_AUX_NATIVE_REPLY_DEFER: + usleep_range(400, 500); + break; + } + } + + DRM_ERROR("too many retries, giving up\n"); + return -EIO; +} + +/** + * drm_dp_dpcd_read() - read a series of bytes from the DPCD + * @aux: DisplayPort AUX channel + * @offset: address of the (first) register to read + * @buffer: buffer to store the register values + * @size: number of bytes in @buffer + * + * Returns the number of bytes transferred on success, or a negative error + * code on failure. -EIO is returned if the request was NAKed by the sink or + * if the retry count was exceeded. If not all bytes were transferred, this + * function returns -EPROTO. Errors from the underlying AUX channel transfer + * function, with the exception of -EBUSY (which causes the transaction to + * be retried), are propagated to the caller. + */ +ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset, + void *buffer, size_t size) +{ + return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset, buffer, + size); +} +EXPORT_SYMBOL(drm_dp_dpcd_read); + +/** + * drm_dp_dpcd_write() - write a series of bytes to the DPCD + * @aux: DisplayPort AUX channel + * @offset: address of the (first) register to write + * @buffer: buffer containing the values to write + * @size: number of bytes in @buffer + * + * Returns the number of bytes transferred on success, or a negative error + * code on failure. -EIO is returned if the request was NAKed by the sink or + * if the retry count was exceeded. If not all bytes were transferred, this + * function returns -EPROTO. Errors from the underlying AUX channel transfer + * function, with the exception of -EBUSY (which causes the transaction to + * be retried), are propagated to the caller. + */ +ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset, + void *buffer, size_t size) +{ + return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_WRITE, offset, buffer, + size); +} +EXPORT_SYMBOL(drm_dp_dpcd_write); diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index 73c3d1f2b20d..0eb29f089e61 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -408,4 +408,83 @@ drm_dp_enhanced_frame_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) (dpcd[DP_MAX_LANE_COUNT] & DP_ENHANCED_FRAME_CAP); }
+/* + * DisplayPort AUX channel + */ + +/** + * struct drm_dp_aux_msg - DisplayPort AUX channel transaction + * @address: address of the (first) register to access + * @request: contains the type of transaction (see DP_AUX_* macros) + * @reply: upon completion, contains the reply type of the transaction + * @buffer: pointer to a transmission or reception buffer + * @size: size of @buffer + */ +struct drm_dp_aux_msg { + unsigned int address; + u8 request; + u8 reply; + void *buffer; + size_t size; +}; + +/** + * struct drm_dp_aux - DisplayPort AUX channel + * @dev: pointer to struct device that is the parent for this AUX channel + * @transfer: transfers a message representing a single AUX transaction + * + * The .dev field should be set to a pointer to the device that implements + * the AUX channel. + * + * Drivers provide a hardware-specific implementation of how transactions + * are executed via the .transfer() function. A pointer to a drm_dp_aux_msg + * structure describing the transaction is passed into this function. Upon + * success, the implementation should return the number of payload bytes + * that were transferred, or a negative error-code on failure. Helpers + * propagate errors from the .transfer() function, with the exception of + * the -EBUSY error, which causes a transaction to be retried. On a short, + * helpers will return -EPROTO to make it simpler to check for failure. + */ +struct drm_dp_aux { + struct device *dev; + + ssize_t (*transfer)(struct drm_dp_aux *aux, + struct drm_dp_aux_msg *msg); +}; + +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, + void *buffer, size_t size); + +/** + * drm_dp_dpcd_readb() - read a single byte from the DPCD + * @aux: DisplayPort AUX channel + * @offset: address of the register to read + * @valuep: location where the value of the register will be stored + * + * Returns the number of bytes transferred (1) on success, or a negative + * error code on failure. + */ +static inline ssize_t drm_dp_dpcd_readb(struct drm_dp_aux *aux, + unsigned int offset, u8 *valuep) +{ + return drm_dp_dpcd_read(aux, offset, valuep, 1); +} + +/** + * drm_dp_dpcd_writeb() - write a single byte to the DPCD + * @aux: DisplayPort AUX channel + * @offset: address of the register to write + * @value: value to write to the register + * + * Returns the number of bytes transferred (1) on success, or a negative + * error code on failure. + */ +static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux, + unsigned int offset, u8 value) +{ + return drm_dp_dpcd_write(aux, offset, &value, 1); +} + #endif /* _DRM_DP_HELPER_H_ */