}
EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);
+#define AUX_RETRY_INTERVAL 500 /* us */
+
/**
* DOC: dp helpers
*
return -EIO;
case DP_AUX_NATIVE_REPLY_DEFER:
- usleep_range(400, 500);
+ usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
break;
}
}
I2C_FUNC_10BIT_ADDR;
}
+static void drm_dp_i2c_msg_write_status_update(struct drm_dp_aux_msg *msg)
+{
+ /*
+ * In case of i2c defer or short i2c ack reply to a write,
+ * we need to switch to WRITE_STATUS_UPDATE to drain the
+ * rest of the message
+ */
+ if ((msg->request & ~DP_AUX_I2C_MOT) == DP_AUX_I2C_WRITE) {
+ msg->request &= DP_AUX_I2C_MOT;
+ msg->request |= DP_AUX_I2C_WRITE_STATUS_UPDATE;
+ }
+}
+
+#define AUX_PRECHARGE_LEN 10 /* 10 to 16 */
+#define AUX_SYNC_LEN (16 + 4) /* preamble + AUX_SYNC_END */
+#define AUX_STOP_LEN 4
+#define AUX_CMD_LEN 4
+#define AUX_ADDRESS_LEN 20
+#define AUX_REPLY_PAD_LEN 4
+#define AUX_LENGTH_LEN 8
+
+/*
+ * Calculate the duration of the AUX request/reply in usec. Gives the
+ * "best" case estimate, ie. successful while as short as possible.
+ */
+static int drm_dp_aux_req_duration(const struct drm_dp_aux_msg *msg)
+{
+ int len = AUX_PRECHARGE_LEN + AUX_SYNC_LEN + AUX_STOP_LEN +
+ AUX_CMD_LEN + AUX_ADDRESS_LEN + AUX_LENGTH_LEN;
+
+ if ((msg->request & DP_AUX_I2C_READ) == 0)
+ len += msg->size * 8;
+
+ return len;
+}
+
+static int drm_dp_aux_reply_duration(const struct drm_dp_aux_msg *msg)
+{
+ int len = AUX_PRECHARGE_LEN + AUX_SYNC_LEN + AUX_STOP_LEN +
+ AUX_CMD_LEN + AUX_REPLY_PAD_LEN;
+
+ /*
+ * For read we expect what was asked. For writes there will
+ * be 0 or 1 data bytes. Assume 0 for the "best" case.
+ */
+ if (msg->request & DP_AUX_I2C_READ)
+ len += msg->size * 8;
+
+ return len;
+}
+
+#define I2C_START_LEN 1
+#define I2C_STOP_LEN 1
+#define I2C_ADDR_LEN 9 /* ADDRESS + R/W + ACK/NACK */
+#define I2C_DATA_LEN 9 /* DATA + ACK/NACK */
+
+/*
+ * Calculate the length of the i2c transfer in usec, assuming
+ * the i2c bus speed is as specified. Gives the the "worst"
+ * case estimate, ie. successful while as long as possible.
+ * Doesn't account the the "MOT" bit, and instead assumes each
+ * message includes a START, ADDRESS and STOP. Neither does it
+ * account for additional random variables such as clock stretching.
+ */
+static int drm_dp_i2c_msg_duration(const struct drm_dp_aux_msg *msg,
+ int i2c_speed_khz)
+{
+ /* AUX bitrate is 1MHz, i2c bitrate as specified */
+ return DIV_ROUND_UP((I2C_START_LEN + I2C_ADDR_LEN +
+ msg->size * I2C_DATA_LEN +
+ I2C_STOP_LEN) * 1000, i2c_speed_khz);
+}
+
+/*
+ * Deterine how many retries should be attempted to successfully transfer
+ * the specified message, based on the estimated durations of the
+ * i2c and AUX transfers.
+ */
+static int drm_dp_i2c_retry_count(const struct drm_dp_aux_msg *msg,
+ int i2c_speed_khz)
+{
+ int aux_time_us = drm_dp_aux_req_duration(msg) +
+ drm_dp_aux_reply_duration(msg);
+ int i2c_time_us = drm_dp_i2c_msg_duration(msg, i2c_speed_khz);
+
+ return DIV_ROUND_UP(i2c_time_us, aux_time_us + AUX_RETRY_INTERVAL);
+}
+
+/*
+ * FIXME currently assumes 10 kHz as some real world devices seem
+ * to require it. We should query/set the speed via DPCD if supported.
+ */
+static int dp_aux_i2c_speed_khz __read_mostly = 10;
+module_param_unsafe(dp_aux_i2c_speed_khz, int, 0644);
+MODULE_PARM_DESC(dp_aux_i2c_speed_khz,
+ "Assumed speed of the i2c bus in kHz, (1-400, default 10)");
+
/*
* Transfer a single I2C-over-AUX message and handle various error conditions,
* retrying the transaction as appropriate. It is assumed that the
*/
static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
{
- unsigned int retry;
+ unsigned int retry, defer_i2c;
int ret;
-
/*
* 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.
+ *
+ * We also try to account for the i2c bus speed.
*/
- for (retry = 0; retry < 7; retry++) {
+ int max_retries = max(7, drm_dp_i2c_retry_count(msg, dp_aux_i2c_speed_khz));
+
+ for (retry = 0, defer_i2c = 0; retry < (max_retries + defer_i2c); retry++) {
mutex_lock(&aux->hw_mutex);
ret = aux->transfer(aux, msg);
mutex_unlock(&aux->hw_mutex);
return -EREMOTEIO;
case DP_AUX_NATIVE_REPLY_DEFER:
- DRM_DEBUG_KMS("native defer");
+ DRM_DEBUG_KMS("native defer\n");
/*
* We could check for I2C bit rate capabilities and if
* available adjust this interval. We could also be
* For now just defer for long enough to hopefully be
* safe for all use-cases.
*/
- usleep_range(500, 600);
+ usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
continue;
default:
* Both native ACK and I2C ACK replies received. We
* can assume the transfer was successful.
*/
+ if (ret != msg->size)
+ drm_dp_i2c_msg_write_status_update(msg);
return ret;
case DP_AUX_I2C_REPLY_NACK:
case DP_AUX_I2C_REPLY_DEFER:
DRM_DEBUG_KMS("I2C defer\n");
+ /* DP Compliance Test 4.2.2.5 Requirement:
+ * Must have at least 7 retries for I2C defers on the
+ * transaction to pass this test
+ */
aux->i2c_defer_count++;
- usleep_range(400, 500);
+ if (defer_i2c < 7)
+ defer_i2c++;
+ usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
+ drm_dp_i2c_msg_write_status_update(msg);
+
continue;
default:
return -EREMOTEIO;
}
+static void drm_dp_i2c_msg_set_request(struct drm_dp_aux_msg *msg,
+ const struct i2c_msg *i2c_msg)
+{
+ msg->request = (i2c_msg->flags & I2C_M_RD) ?
+ DP_AUX_I2C_READ : DP_AUX_I2C_WRITE;
+ msg->request |= DP_AUX_I2C_MOT;
+}
+
/*
* Keep retrying drm_dp_i2c_do_msg until all data has been transferred.
*
for (i = 0; i < num; i++) {
msg.address = msgs[i].addr;
- msg.request = (msgs[i].flags & I2C_M_RD) ?
- DP_AUX_I2C_READ :
- DP_AUX_I2C_WRITE;
- msg.request |= DP_AUX_I2C_MOT;
+ drm_dp_i2c_msg_set_request(&msg, &msgs[i]);
/* Send a bare address packet to start the transaction.
* Zero sized messages specify an address only (bare
* address) transaction.
msg.buffer = NULL;
msg.size = 0;
err = drm_dp_i2c_do_msg(aux, &msg);
+
+ /*
+ * Reset msg.request in case in case it got
+ * changed into a WRITE_STATUS_UPDATE.
+ */
+ drm_dp_i2c_msg_set_request(&msg, &msgs[i]);
+
if (err < 0)
break;
/* We want each transaction to be as large as possible, but
msg.size = min(transfer_size, msgs[i].len - j);
err = drm_dp_i2c_drain_msg(aux, &msg);
+
+ /*
+ * Reset msg.request in case in case it got
+ * changed into a WRITE_STATUS_UPDATE.
+ */
+ drm_dp_i2c_msg_set_request(&msg, &msgs[i]);
+
if (err < 0)
break;
transfer_size = err;
Code Review / kvmfornfv.git / blobdiff