Commit c197db75 authored by Thierry Reding's avatar Thierry Reding

drm/dp: Add AUX channel infrastructure

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: default avatarAlex Deucher <alexander.deucher@amd.com>
Reviewed-by: default avatarJani Nikula <jani.nikula@intel.com>
Signed-off-by: default avatarThierry 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
parent 38dbfb59
......@@ -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);
......@@ -398,4 +398,83 @@ 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_ */
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