On Tue, 21 Jan 2014, Thierry Reding thierry.reding@gmail.com wrote:
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 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 | 67 ++++++++++++++++++++++++ 2 files changed, 177 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 9e978aae8972..3e74ed93b19f 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.
- The .transfer() function is the hardware-specific implementation of how
- a transaction is executed on the AUX channel. A pointer to a struct
- drm_dp_aux_msg describing the transaction is passed into this function.
- Upon success, the implementation should return the number of 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.
A little more bikeshedding... ;)
Might be useful to clarify that the .transfer() function must return the number of *payload* bytes that were transferred.
The documentation of the .transfer() function might be better suited within struct drm_dp_aux where it's actually defined.
BR, Jani.
- The .dev field should be set to a pointer to the device that implements
- the AUX channel.
- */
+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 == 0)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 no bytes were transferred, -EPROTO is
- returned. Errors from the underlying AUX channel transfer function, with
- the exception of -EBUSY (upon which the transaction will 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 no bytes were transferred, -EPROTO is
- returned. Errors from the underlying AUX channel transfer function, with
- the exception of -EBUSY (upon which the transaction will 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 1d09050a8c00..c69c1dc1b741 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -398,4 +398,71 @@ 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
- */
+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_ */
1.8.4.2