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.
Signed-off-by: Thierry Reding treding@nvidia.com --- Changes in v3: - add back DRM_DEBUG_KMS and DRM_ERROR messages - embed i2c_adapter within struct drm_dp_aux - fix typo in comment
drivers/gpu/drm/drm_dp_helper.c | 183 ++++++++++++++++++++++++++++++++++++++++ include/drm/drm_dp_helper.h | 5 ++ 2 files changed, 188 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index ac2e12789634..dc25f63bbb0b 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -364,6 +364,13 @@ EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate); * * The .dev field should be set to a pointer to the device that implements * the AUX channel. + * + * 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, @@ -566,3 +573,179 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
return 0; } + +/* + * 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; + } + + 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 bitrate 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 (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); diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index c7b3c736c40a..4d67bd12089b 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -421,10 +421,12 @@ 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 */ struct drm_dp_aux { + struct i2c_adapter ddc; struct device *dev;
ssize_t (*transfer)(struct drm_dp_aux *aux, @@ -485,4 +487,7 @@ 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_ */