[PATCH v2] soundwire: qcom: wait for fifo space to be available before read/write

[Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>]

If we write registers very fast we can endup in a situation where some
of the writes will be dropped without any notice.

So wait for the fifo space to be available before reading/writing the
soundwire registers.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
---

Changes since v1:
        merged some of the loop code to make it simple as suggested by Pierre
        updated error code and comments as suggested by Vinod


 drivers/soundwire/qcom.c | 66 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/drivers/soundwire/qcom.c b/drivers/soundwire/qcom.c
index 6affa3cd4039..5fd4a99cc8ac 100644
--- a/drivers/soundwire/qcom.c
+++ b/drivers/soundwire/qcom.c
@@ -24,6 +24,8 @@
 #define SWRM_COMP_CFG_IRQ_LEVEL_OR_PULSE_MSK			BIT(1)
 #define SWRM_COMP_CFG_ENABLE_MSK				BIT(0)
 #define SWRM_COMP_PARAMS					0x100
+#define SWRM_COMP_PARAMS_WR_FIFO_DEPTH				GENMASK(14, 10)
+#define SWRM_COMP_PARAMS_RD_FIFO_DEPTH				GENMASK(19, 15)
 #define SWRM_COMP_PARAMS_DOUT_PORTS_MASK			GENMASK(4, 0)
 #define SWRM_COMP_PARAMS_DIN_PORTS_MASK				GENMASK(9, 5)
 #define SWRM_INTERRUPT_STATUS					0x200
@@ -51,6 +53,8 @@
 #define SWRM_CMD_FIFO_CMD					0x308
 #define SWRM_CMD_FIFO_FLUSH					0x1
 #define SWRM_CMD_FIFO_STATUS					0x30C
+#define SWRM_RD_CMD_FIFO_CNT_MASK				GENMASK(20, 16)
+#define SWRM_WR_CMD_FIFO_CNT_MASK				GENMASK(12, 8)
 #define SWRM_CMD_FIFO_CFG_ADDR					0x314
 #define SWRM_CONTINUE_EXEC_ON_CMD_IGNORE			BIT(31)
 #define SWRM_RD_WR_CMD_RETRIES					0x7
@@ -104,6 +108,7 @@
 #define SWR_BROADCAST_CMD_ID    0x0F
 #define SWR_MAX_CMD_ID	14
 #define MAX_FIFO_RD_RETRY 3
+#define SWR_OVERFLOW_RETRY_COUNT 30
 
 struct qcom_swrm_port_config {
 	u8 si;
@@ -147,6 +152,8 @@ struct qcom_swrm_ctrl {
 	int (*reg_read)(struct qcom_swrm_ctrl *ctrl, int reg, u32 *val);
 	int (*reg_write)(struct qcom_swrm_ctrl *ctrl, int reg, int val);
 	u32 slave_status;
+	u32 wr_fifo_depth;
+	u32 rd_fifo_depth;
 };
 
 struct qcom_swrm_data {
@@ -238,6 +245,55 @@ static u32 swrm_get_packed_reg_val(u8 *cmd_id, u8 cmd_data,
 	return val;
 }
 
+static int swrm_wait_for_rd_fifo_avail(struct qcom_swrm_ctrl *swrm)
+{
+	u32 fifo_outstanding_data, value;
+	int fifo_retry_count = SWR_OVERFLOW_RETRY_COUNT;
+
+	do {
+		/* Check for fifo underflow during read */
+		swrm->reg_read(swrm, SWRM_CMD_FIFO_STATUS, &value);
+		fifo_outstanding_data = FIELD_GET(SWRM_RD_CMD_FIFO_CNT_MASK, value);
+
+		/* Check if read data is available in read fifo */
+		if (fifo_outstanding_data > 0)
+			return 0;
+
+		usleep_range(500, 510);
+	} while (fifo_retry_count--);
+
+	if (fifo_outstanding_data == 0) {
+		dev_err_ratelimited(swrm->dev, "%s err read underflow\n", __func__);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int swrm_wait_for_wr_fifo_avail(struct qcom_swrm_ctrl *swrm)
+{
+	u32 fifo_outstanding_cmds, value;
+	int fifo_retry_count = SWR_OVERFLOW_RETRY_COUNT;
+
+	do {
+		/* Check for fifo overflow during write */
+		swrm->reg_read(swrm, SWRM_CMD_FIFO_STATUS, &value);
+		fifo_outstanding_cmds = FIELD_GET(SWRM_WR_CMD_FIFO_CNT_MASK, value);
+
+		/* Check for space in write fifo before writing */
+		if (fifo_outstanding_cmds < swrm->wr_fifo_depth)
+			return 0;
+
+		usleep_range(500, 510);
+	} while (fifo_retry_count--);
+
+	if (fifo_outstanding_cmds == swrm->wr_fifo_depth) {
+		dev_err_ratelimited(swrm->dev, "%s err write overflow\n", __func__);
+		return -EIO;
+	}
+
+	return 0;
+}
 
 static int qcom_swrm_cmd_fifo_wr_cmd(struct qcom_swrm_ctrl *swrm, u8 cmd_data,
 				     u8 dev_addr, u16 reg_addr)
@@ -256,6 +312,9 @@ static int qcom_swrm_cmd_fifo_wr_cmd(struct qcom_swrm_ctrl *swrm, u8 cmd_data,
 					      dev_addr, reg_addr);
 	}
 
+	if (swrm_wait_for_wr_fifo_avail(swrm))
+		return SDW_CMD_FAIL_OTHER;
+
 	/* Its assumed that write is okay as we do not get any status back */
 	swrm->reg_write(swrm, SWRM_CMD_FIFO_WR_CMD, val);
 
@@ -295,6 +354,9 @@ static int qcom_swrm_cmd_fifo_rd_cmd(struct qcom_swrm_ctrl *swrm,
 	/* wait for FIFO RD CMD complete to avoid overflow */
 	usleep_range(250, 255);
 
+	if (swrm_wait_for_rd_fifo_avail(swrm))
+		return SDW_CMD_FAIL_OTHER;
+
 	do {
 		swrm->reg_read(swrm, SWRM_CMD_FIFO_RD_FIFO_ADDR, &cmd_data);
 		rval[0] = cmd_data & 0xFF;
@@ -586,6 +648,10 @@ static int qcom_swrm_init(struct qcom_swrm_ctrl *ctrl)
 				SWRM_INTERRUPT_STATUS_RMSK);
 	}
 	ctrl->slave_status = 0;
+	ctrl->reg_read(ctrl, SWRM_COMP_PARAMS, &val);
+	ctrl->rd_fifo_depth = FIELD_GET(SWRM_COMP_PARAMS_RD_FIFO_DEPTH, val);
+	ctrl->wr_fifo_depth = FIELD_GET(SWRM_COMP_PARAMS_WR_FIFO_DEPTH, val);
+
 	return 0;
 }
 
-- 
2.21.0