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@xxxxxxxxxx>
---
drivers/gpu/drm/drm_dp_helper.c | 178 ++++++++++++++++++++++++++++++++++++++++
include/drm/drm_dp_helper.h | 4 +
2 files changed, 182 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 01a8173c6e83..8a64cf8ac8cc 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -555,3 +555,181 @@ int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link)
return 0;
}
+
+/*
+ * I2C-over-AUX implementation
+ */
+
+struct drm_dp_i2c_adapter {
+ struct i2c_adapter adapter;
+ struct drm_dp_aux *aux;
+};
+
+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)
+ 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:
+ return -EREMOTEIO;
+
+ case DP_AUX_NATIVE_REPLY_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 forc 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:
+ return -EREMOTEIO;
+
+ case DP_AUX_I2C_REPLY_DEFER:
+ 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_i2c_adapter *dp = 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(dp->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_add_i2c_bus() - register an I2C adapter for I2C-over-AUX access
+ * @aux: DisplayPort AUX channel
+ *
+ * Returns a pointer to an I2C adapter on success or an ERR_PTR()-encoded
+ * error code on failure.
+ */
+struct i2c_adapter *drm_dp_add_i2c_bus(struct drm_dp_aux *aux)
+{
+ struct drm_dp_i2c_adapter *adapter;
+ int err;
+
+ adapter = kzalloc(sizeof(*adapter), GFP_KERNEL);
+ if (!adapter)
+ return ERR_PTR(-ENOMEM);
+
+ adapter->adapter.algo = &drm_dp_i2c_algo;
+ adapter->adapter.algo_data = adapter;
+ adapter->adapter.retries = 3;
+ adapter->aux = aux;
+
+ adapter->adapter.class = I2C_CLASS_DDC;
+ adapter->adapter.owner = THIS_MODULE;
+ adapter->adapter.dev.parent = aux->dev;
+ adapter->adapter.dev.of_node = aux->dev->of_node;
+
+ strncpy(adapter->adapter.name, dev_name(aux->dev),
+ sizeof(adapter->adapter.name));
+
+ err = i2c_add_adapter(&adapter->adapter);
+ if (err < 0) {
+ kfree(adapter);
+ return ERR_PTR(err);
+ }
+
+ return &adapter->adapter;
+}
+EXPORT_SYMBOL(drm_dp_add_i2c_bus);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index bad9ee11a2e2..c4acdbc2a172 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -423,6 +423,8 @@ struct drm_dp_aux_msg {
* @transfer: transfers a message representing a single AUX transaction
*/
struct drm_dp_aux {
+ struct device *dev;
+
ssize_t (*transfer)(struct drm_dp_aux *aux,
struct drm_dp_aux_msg *msg);
};
@@ -494,4 +496,6 @@ 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);
+struct i2c_adapter *drm_dp_add_i2c_bus(struct drm_dp_aux *aux);
+
#endif /* _DRM_DP_HELPER_H_ */
--
1.8.4.2
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