Merge tag 'v4.3-rc2' into topic/drm-misc

[cascardo/linux.git] / drivers / gpu / drm / drm_dp_helper.c

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 5a55d90..9535c5b 100644 (file)
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -159,6 +159,8 @@ int drm_dp_bw_code_to_link_rate(u8 link_bw)
 }
 EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);
 
+#define AUX_RETRY_INTERVAL 500 /* us */
+
 /**
  * DOC: dp helpers
  *
@@ -213,7 +215,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
                        return -EIO;
 
                case DP_AUX_NATIVE_REPLY_DEFER:
-                       usleep_range(400, 500);
+                       usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
                        break;
                }
        }
@@ -435,6 +437,90 @@ static void drm_dp_i2c_msg_write_status_update(struct drm_dp_aux_msg *msg)
        }
 }
 
+#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
@@ -447,13 +533,16 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 {
        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, defer_i2c = 0; retry < (7 + defer_i2c); 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);
@@ -489,7 +578,7 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
                         * 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:
@@ -521,8 +610,9 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
                        aux->i2c_defer_count++;
                        if (defer_i2c < 7)
                                defer_i2c++;
-                       usleep_range(400, 500);
+                       usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
                        drm_dp_i2c_msg_write_status_update(msg);
+
                        continue;
 
                default: