Commit 88759686 authored by Thierry Reding's avatar Thierry Reding
Browse files

drm/dp: Allow registering AUX channels as I2C busses 



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: 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 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
parent 516c0f7c

drivers/gpu/drm/drm_dp_helper.c

+179 −7
Original line number Diff line number Diff line
@@ -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);

include/drm/drm_dp_helper.h

+12 −0
Original line number Diff line number Diff line
@@ -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_ */

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