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: 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
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@ -357,13 +357,6 @@ EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);
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* Transactions are described using a hardware-independent drm_dp_aux_msg
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* Transactions are described using a hardware-independent drm_dp_aux_msg
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* structure, which is passed into a driver's .transfer() implementation.
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* structure, which is passed into a driver's .transfer() implementation.
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* Both native and I2C-over-AUX transactions are supported.
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* Both native and I2C-over-AUX transactions are supported.
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*
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* An AUX channel can also be used to transport I2C messages to a sink. A
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* typical application of that is to access an EDID that's present in the
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* sink device. The .transfer() function can also be used to execute such
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* transactions. The drm_dp_aux_register_i2c_bus() function registers an
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* I2C adapter that can be passed to drm_probe_ddc(). Upon removal, drivers
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* should call drm_dp_aux_unregister_i2c_bus() to remove the I2C adapter.
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*/
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*/
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static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
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static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
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@ -569,3 +562,182 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
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return 0;
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return 0;
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}
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}
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EXPORT_SYMBOL(drm_dp_link_configure);
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EXPORT_SYMBOL(drm_dp_link_configure);
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/*
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* I2C-over-AUX implementation
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*/
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static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
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{
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return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
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I2C_FUNC_SMBUS_READ_BLOCK_DATA |
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I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
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I2C_FUNC_10BIT_ADDR;
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}
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/*
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* Transfer a single I2C-over-AUX message and handle various error conditions,
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* retrying the transaction as appropriate.
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*/
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static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
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{
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unsigned int retry;
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int err;
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/*
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* DP1.2 sections 2.7.7.1.5.6.1 and 2.7.7.1.6.6.1: A DP Source device
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* is required to retry at least seven times upon receiving AUX_DEFER
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* before giving up the AUX transaction.
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*/
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for (retry = 0; retry < 7; retry++) {
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err = aux->transfer(aux, msg);
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if (err < 0) {
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if (err == -EBUSY)
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continue;
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DRM_DEBUG_KMS("transaction failed: %d\n", err);
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return err;
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}
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if (err < msg->size)
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return -EPROTO;
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switch (msg->reply & DP_AUX_NATIVE_REPLY_MASK) {
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case DP_AUX_NATIVE_REPLY_ACK:
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/*
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* For I2C-over-AUX transactions this isn't enough, we
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* need to check for the I2C ACK reply.
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*/
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break;
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case DP_AUX_NATIVE_REPLY_NACK:
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DRM_DEBUG_KMS("native nack\n");
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return -EREMOTEIO;
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case DP_AUX_NATIVE_REPLY_DEFER:
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DRM_DEBUG_KMS("native defer");
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/*
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* We could check for I2C bit rate capabilities and if
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* available adjust this interval. We could also be
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* more careful with DP-to-legacy adapters where a
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* long legacy cable may force very low I2C bit rates.
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*
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* For now just defer for long enough to hopefully be
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* safe for all use-cases.
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*/
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usleep_range(500, 600);
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continue;
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default:
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DRM_ERROR("invalid native reply %#04x\n", msg->reply);
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return -EREMOTEIO;
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}
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switch (msg->reply & DP_AUX_I2C_REPLY_MASK) {
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case DP_AUX_I2C_REPLY_ACK:
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/*
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* Both native ACK and I2C ACK replies received. We
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* can assume the transfer was successful.
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*/
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return 0;
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case DP_AUX_I2C_REPLY_NACK:
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DRM_DEBUG_KMS("I2C nack\n");
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return -EREMOTEIO;
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case DP_AUX_I2C_REPLY_DEFER:
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DRM_DEBUG_KMS("I2C defer\n");
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usleep_range(400, 500);
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continue;
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default:
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DRM_ERROR("invalid I2C reply %#04x\n", msg->reply);
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return -EREMOTEIO;
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}
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}
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DRM_ERROR("too many retries, giving up\n");
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return -EREMOTEIO;
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}
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static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
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int num)
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{
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struct drm_dp_aux *aux = adapter->algo_data;
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unsigned int i, j;
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for (i = 0; i < num; i++) {
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struct drm_dp_aux_msg msg;
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int err;
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/*
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* Many hardware implementations support FIFOs larger than a
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* single byte, but it has been empirically determined that
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* transferring data in larger chunks can actually lead to
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* decreased performance. Therefore each message is simply
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* transferred byte-by-byte.
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*/
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for (j = 0; j < msgs[i].len; j++) {
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memset(&msg, 0, sizeof(msg));
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msg.address = msgs[i].addr;
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msg.request = (msgs[i].flags & I2C_M_RD) ?
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DP_AUX_I2C_READ :
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DP_AUX_I2C_WRITE;
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/*
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* All messages except the last one are middle-of-
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* transfer messages.
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*/
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if ((i < num - 1) || (j < msgs[i].len - 1))
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msg.request |= DP_AUX_I2C_MOT;
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msg.buffer = msgs[i].buf + j;
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msg.size = 1;
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err = drm_dp_i2c_do_msg(aux, &msg);
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if (err < 0)
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return err;
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}
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}
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return num;
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}
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static const struct i2c_algorithm drm_dp_i2c_algo = {
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.functionality = drm_dp_i2c_functionality,
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.master_xfer = drm_dp_i2c_xfer,
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};
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/**
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* drm_dp_aux_register_i2c_bus() - register an I2C adapter for I2C-over-AUX
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* @aux: DisplayPort AUX channel
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*
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* Returns 0 on success or a negative error code on failure.
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*/
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int drm_dp_aux_register_i2c_bus(struct drm_dp_aux *aux)
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{
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aux->ddc.algo = &drm_dp_i2c_algo;
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aux->ddc.algo_data = aux;
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aux->ddc.retries = 3;
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aux->ddc.class = I2C_CLASS_DDC;
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aux->ddc.owner = THIS_MODULE;
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aux->ddc.dev.parent = aux->dev;
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aux->ddc.dev.of_node = aux->dev->of_node;
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strncpy(aux->ddc.name, dev_name(aux->dev), sizeof(aux->ddc.name));
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return i2c_add_adapter(&aux->ddc);
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}
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EXPORT_SYMBOL(drm_dp_aux_register_i2c_bus);
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/**
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* drm_dp_aux_unregister_i2c_bus() - unregister an I2C-over-AUX adapter
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* @aux: DisplayPort AUX channel
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*/
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void drm_dp_aux_unregister_i2c_bus(struct drm_dp_aux *aux)
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{
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i2c_del_adapter(&aux->ddc);
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}
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EXPORT_SYMBOL(drm_dp_aux_unregister_i2c_bus);
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@ -421,6 +421,7 @@ struct drm_dp_aux_msg {
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/**
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/**
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* struct drm_dp_aux - DisplayPort AUX channel
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* struct drm_dp_aux - DisplayPort AUX channel
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* @ddc: I2C adapter that can be used for I2C-over-AUX communication
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* @dev: pointer to struct device that is the parent for this AUX channel
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* @dev: pointer to struct device that is the parent for this AUX channel
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* @transfer: transfers a message representing a single AUX transaction
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* @transfer: transfers a message representing a single AUX transaction
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*
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*
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@ -435,8 +436,16 @@ struct drm_dp_aux_msg {
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* propagate errors from the .transfer() function, with the exception of
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* propagate errors from the .transfer() function, with the exception of
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* the -EBUSY error, which causes a transaction to be retried. On a short,
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* the -EBUSY error, which causes a transaction to be retried. On a short,
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* helpers will return -EPROTO to make it simpler to check for failure.
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* helpers will return -EPROTO to make it simpler to check for failure.
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*
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* An AUX channel can also be used to transport I2C messages to a sink. A
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* typical application of that is to access an EDID that's present in the
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* sink device. The .transfer() function can also be used to execute such
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* transactions. The drm_dp_aux_register_i2c_bus() function registers an
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* I2C adapter that can be passed to drm_probe_ddc(). Upon removal, drivers
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* should call drm_dp_aux_unregister_i2c_bus() to remove the I2C adapter.
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*/
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*/
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struct drm_dp_aux {
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struct drm_dp_aux {
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struct i2c_adapter ddc;
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struct device *dev;
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struct device *dev;
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ssize_t (*transfer)(struct drm_dp_aux *aux,
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ssize_t (*transfer)(struct drm_dp_aux *aux,
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@ -497,4 +506,7 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link);
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int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);
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int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);
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int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
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int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
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int drm_dp_aux_register_i2c_bus(struct drm_dp_aux *aux);
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void drm_dp_aux_unregister_i2c_bus(struct drm_dp_aux *aux);
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#endif /* _DRM_DP_HELPER_H_ */
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#endif /* _DRM_DP_HELPER_H_ */
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