From 4d6d5f1d08d2138dc43b28966eb6200e3db2e623 Mon Sep 17 00:00:00 2001 From: Russell King Date: Fri, 18 Nov 2016 19:40:10 +0000 Subject: [PATCH] i2c: designware: fix rx fifo depth tracking When loading the TX fifo to receive bytes on the I2C bus, we incorrectly count the number of bytes: rx_limit = dev->rx_fifo_depth - dw_readl(dev, DW_IC_RXFLR); while (buf_len > 0 && tx_limit > 0 && rx_limit > 0) { if (rx_limit - dev->rx_outstanding <= 0) break; rx_limit--; dev->rx_outstanding++; } DW_IC_RXFLR indicates how many bytes are available to be read in the FIFO, dev->rx_fifo_depth is the FIFO size, and dev->rx_outstanding is the number of bytes that we've requested to be read so far, but which have not been read. Firstly, increasing dev->rx_outstanding and decreasing rx_limit and then comparing them results in each byte consuming "two" bytes in this tracking, so this is obviously wrong. Secondly, the number of bytes that _could_ be received into the FIFO at any time is the number of bytes we have so far requested but not yet read from the FIFO - in other words dev->rx_outstanding. So, in order to request enough bytes to fill the RX FIFO, we need to request dev->rx_fifo_depth - dev->rx_outstanding bytes. Modifying the code thusly results in us reaching the maximum number of bytes outstanding each time we queue more "receive" operations, provided the transfer allows that to happen. Signed-off-by: Russell King Reviewed-by: Mika Westerberg Acked-by: Jarkko Nikula Signed-off-by: Wolfram Sang --- drivers/i2c/busses/i2c-designware-core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c index 066a2ba6aeda..c53058d6139c 100644 --- a/drivers/i2c/busses/i2c-designware-core.c +++ b/drivers/i2c/busses/i2c-designware-core.c @@ -611,7 +611,7 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev) if (msgs[dev->msg_write_idx].flags & I2C_M_RD) { /* avoid rx buffer overrun */ - if (rx_limit - dev->rx_outstanding <= 0) + if (dev->rx_outstanding >= dev->rx_fifo_depth) break; dw_writel(dev, cmd | 0x100, DW_IC_DATA_CMD); -- 2.20.1