diff options
Diffstat (limited to 'drivers/gpu/drm/drm_dp_helper.c')
| -rw-r--r-- | drivers/gpu/drm/drm_dp_helper.c | 99 |
1 files changed, 94 insertions, 5 deletions
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 80a02a412607..291734e87fca 100644 --- 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; } } @@ -422,6 +424,90 @@ static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter) I2C_FUNC_10BIT_ADDR; } +#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 @@ -434,13 +520,16 @@ 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); @@ -476,7 +565,7 @@ 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: @@ -506,7 +595,7 @@ 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); continue; default: |