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drm/dp: Allow registering AUX channels as I2C busses

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Implements an I2C-over-AUX I2C adapter on top of the generic drm_dp_aux
infrastructure. It extracts the retry logic from existing drivers, which
should help in porting those drivers to this new helper.

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 to header file
- keep MOT set between I2C messages
- return -EPROTO on short reads

Changes in v4:
- fix typo "bitrate" -> "bit rate"

Changes in v3:
- add back DRM_DEBUG_KMS and DRM_ERROR messages
- embed i2c_adapter within struct drm_dp_aux
- fix typo in comment
This commit is contained in:
Thierry Reding 2013-12-12 09:57:53 +01:00
parent 516c0f7c0a
commit 88759686c7
2 changed files with 191 additions and 7 deletions
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186
drivers/gpu/drm/drm_dp_helper.c
View File

@ -357,13 +357,6 @@ EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);
* 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,
@ -569,3 +562,182 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
return 0;
}
EXPORT_SYMBOL(drm_dp_link_configure);
/*
* I2C-over-AUX implementation
*/
static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
{
return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
I2C_FUNC_SMBUS_READ_BLOCK_DATA |
I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
I2C_FUNC_10BIT_ADDR;
}
/*
* Transfer a single I2C-over-AUX message and handle various error conditions,
* retrying the transaction as appropriate.
*/
static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
{
unsigned int retry;
int err;
/*
* DP1.2 sections 2.7.7.1.5.6.1 and 2.7.7.1.6.6.1: A DP Source device
* is required to retry at least seven times upon receiving AUX_DEFER
* before giving up the AUX transaction.
*/
for (retry = 0; retry < 7; retry++) {
err = aux->transfer(aux, msg);
if (err < 0) {
if (err == -EBUSY)
continue;
DRM_DEBUG_KMS("transaction failed: %d\n", err);
return err;
}
if (err < msg->size)
return -EPROTO;
switch (msg->reply & DP_AUX_NATIVE_REPLY_MASK) {
case DP_AUX_NATIVE_REPLY_ACK:
/*
* For I2C-over-AUX transactions this isn't enough, we
* need to check for the I2C ACK reply.
*/
break;
case DP_AUX_NATIVE_REPLY_NACK:
DRM_DEBUG_KMS("native nack\n");
return -EREMOTEIO;
case DP_AUX_NATIVE_REPLY_DEFER:
DRM_DEBUG_KMS("native defer");
/*
* We could check for I2C bit rate capabilities and if
* available adjust this interval. We could also be
* more careful with DP-to-legacy adapters where a
* long legacy cable may force very low I2C bit rates.
*
* For now just defer for long enough to hopefully be
* safe for all use-cases.
*/
usleep_range(500, 600);
continue;
default:
DRM_ERROR("invalid native reply %#04x\n", msg->reply);
return -EREMOTEIO;
}
switch (msg->reply & DP_AUX_I2C_REPLY_MASK) {
case DP_AUX_I2C_REPLY_ACK:
/*
* Both native ACK and I2C ACK replies received. We
* can assume the transfer was successful.
*/
return 0;
case DP_AUX_I2C_REPLY_NACK:
DRM_DEBUG_KMS("I2C nack\n");
return -EREMOTEIO;
case DP_AUX_I2C_REPLY_DEFER:
DRM_DEBUG_KMS("I2C defer\n");
usleep_range(400, 500);
continue;
default:
DRM_ERROR("invalid I2C reply %#04x\n", msg->reply);
return -EREMOTEIO;
}
}
DRM_ERROR("too many retries, giving up\n");
return -EREMOTEIO;
}
static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
int num)
{
struct drm_dp_aux *aux = adapter->algo_data;
unsigned int i, j;
for (i = 0; i < num; i++) {
struct drm_dp_aux_msg msg;
int err;
/*
* Many hardware implementations support FIFOs larger than a
* single byte, but it has been empirically determined that
* transferring data in larger chunks can actually lead to
* decreased performance. Therefore each message is simply
* transferred byte-by-byte.
*/
for (j = 0; j < msgs[i].len; j++) {
memset(&msg, 0, sizeof(msg));
msg.address = msgs[i].addr;
msg.request = (msgs[i].flags & I2C_M_RD) ?
DP_AUX_I2C_READ :
DP_AUX_I2C_WRITE;
/*
* All messages except the last one are middle-of-
* transfer messages.
*/
if ((i < num - 1) || (j < msgs[i].len - 1))
msg.request |= DP_AUX_I2C_MOT;
msg.buffer = msgs[i].buf + j;
msg.size = 1;
err = drm_dp_i2c_do_msg(aux, &msg);
if (err < 0)
return err;
}
}
return num;
}
static const struct i2c_algorithm drm_dp_i2c_algo = {
.functionality = drm_dp_i2c_functionality,
.master_xfer = drm_dp_i2c_xfer,
};
/**
* drm_dp_aux_register_i2c_bus() - register an I2C adapter for I2C-over-AUX
* @aux: DisplayPort AUX channel
*
* Returns 0 on success or a negative error code on failure.
*/
int drm_dp_aux_register_i2c_bus(struct drm_dp_aux *aux)
{
aux->ddc.algo = &drm_dp_i2c_algo;
aux->ddc.algo_data = aux;
aux->ddc.retries = 3;
aux->ddc.class = I2C_CLASS_DDC;
aux->ddc.owner = THIS_MODULE;
aux->ddc.dev.parent = aux->dev;
aux->ddc.dev.of_node = aux->dev->of_node;
strncpy(aux->ddc.name, dev_name(aux->dev), sizeof(aux->ddc.name));
return i2c_add_adapter(&aux->ddc);
}
EXPORT_SYMBOL(drm_dp_aux_register_i2c_bus);
/**
* drm_dp_aux_unregister_i2c_bus() - unregister an I2C-over-AUX adapter
* @aux: DisplayPort AUX channel
*/
void drm_dp_aux_unregister_i2c_bus(struct drm_dp_aux *aux)
{
i2c_del_adapter(&aux->ddc);
}
EXPORT_SYMBOL(drm_dp_aux_unregister_i2c_bus);

12
include/drm/drm_dp_helper.h
View File

@ -421,6 +421,7 @@ struct drm_dp_aux_msg {
/**
* struct drm_dp_aux - DisplayPort AUX channel
* @ddc: I2C adapter that can be used for I2C-over-AUX communication
* @dev: pointer to struct device that is the parent for this AUX channel
* @transfer: transfers a message representing a single AUX transaction
*
@ -435,8 +436,16 @@ struct drm_dp_aux_msg {
* 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.
*
* 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.
*/
struct drm_dp_aux {
struct i2c_adapter ddc;
struct device *dev;
ssize_t (*transfer)(struct drm_dp_aux *aux,
@ -497,4 +506,7 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link);
int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);
int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
int drm_dp_aux_register_i2c_bus(struct drm_dp_aux *aux);
void drm_dp_aux_unregister_i2c_bus(struct drm_dp_aux *aux);
#endif /* _DRM_DP_HELPER_H_ */