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spi: spi-cadence: Avoid read of RX FIFO before its ready

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Recent changes to cdns_spi_irq introduced some issues.

Firstly, when writing the end of a longer transaction, the code in
cdns_spi_irq will write data into the TX FIFO, then immediately
fall into the if (!xspi->tx_bytes) path and attempt to read data
from the RX FIFO. However this required waiting for the TX FIFO to
empty before the RX data was ready.

Secondly, the variable trans_cnt is now rather inaccurately named
since in cases, where the watermark is set to 1, trans_cnt will be
1 but the count of bytes transferred would be much longer.

Finally, when setting up the transaction we set the watermark to 50%
of the FIFO if the transaction is great than 50% of the FIFO. However,
there is no need to split a tranaction that is smaller than the
whole FIFO, so anything up to the FIFO size can be done in a single
transaction.

Tidy up the code a little, to avoid repeatedly calling
cdns_spi_read_rx_fifo with a count of 1, and correct the three issues
noted above.

Fixes: b1b90514ea ("spi: spi-cadence: Add support for Slave mode")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com
Link: https://lore.kernel.org/r/20230509164153.3907694-1-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org
This commit is contained in:
Charles Keepax 2023-05-09 17:41:52 +01:00 • committed by Mark Brown
parent 4c329f5da7
commit a84c11e16d
No known key found for this signature in database
GPG key ID: 24D68B725D5487D0
1 changed files with 14 additions and 26 deletions
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40
drivers/spi/spi-cadence.c
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@ -304,13 +304,11 @@ static int cdns_spi_setup_transfer(struct spi_device *spi,
* cdns_spi_fill_tx_fifo - Fills the TX FIFO with as many bytes as possible * cdns_spi_fill_tx_fifo - Fills the TX FIFO with as many bytes as possible
* @xspi: Pointer to the cdns_spi structure * @xspi: Pointer to the cdns_spi structure
*/ */
static void cdns_spi_fill_tx_fifo(struct cdns_spi *xspi) static void cdns_spi_fill_tx_fifo(struct cdns_spi *xspi, unsigned int avail)
{ {
unsigned long trans_cnt = 0; unsigned long trans_cnt = 0;
while ((trans_cnt < xspi->tx_fifo_depth) && while ((trans_cnt < avail) && (xspi->tx_bytes > 0)) {
(xspi->tx_bytes > 0)) {
/* When xspi in busy condition, bytes may send failed, /* When xspi in busy condition, bytes may send failed,
* then spi control did't work thoroughly, add one byte delay * then spi control did't work thoroughly, add one byte delay
*/ */
@ -381,33 +379,23 @@ static irqreturn_t cdns_spi_irq(int irq, void *dev_id)
spi_finalize_current_transfer(ctlr); spi_finalize_current_transfer(ctlr);
status = IRQ_HANDLED; status = IRQ_HANDLED;
} else if (intr_status & CDNS_SPI_IXR_TXOW) { } else if (intr_status & CDNS_SPI_IXR_TXOW) {
int trans_cnt = cdns_spi_read(xspi, CDNS_SPI_THLD); int threshold = cdns_spi_read(xspi, CDNS_SPI_THLD);
int trans_cnt = xspi->rx_bytes - xspi->tx_bytes;
if (threshold > 1)
trans_cnt -= threshold;
/* Set threshold to one if number of pending are /* Set threshold to one if number of pending are
* less than half fifo * less than half fifo
*/ */
if (xspi->tx_bytes < xspi->tx_fifo_depth >> 1) if (xspi->tx_bytes < xspi->tx_fifo_depth >> 1)
cdns_spi_write(xspi, CDNS_SPI_THLD, 1); cdns_spi_write(xspi, CDNS_SPI_THLD, 1);
while (trans_cnt) { cdns_spi_read_rx_fifo(xspi, trans_cnt);
cdns_spi_read_rx_fifo(xspi, 1);
if (xspi->tx_bytes) { if (xspi->tx_bytes) {
if (xspi->txbuf) cdns_spi_fill_tx_fifo(xspi, trans_cnt);
cdns_spi_write(xspi, CDNS_SPI_TXD, } else {
*xspi->txbuf++);
else
cdns_spi_write(xspi, CDNS_SPI_TXD, 0);
xspi->tx_bytes--;
}
trans_cnt--;
}
if (!xspi->tx_bytes) {
/* Fixed delay due to controller limitation with
* RX_NEMPTY incorrect status
* Xilinx AR:65885 contains more details
*/
udelay(10);
cdns_spi_read_rx_fifo(xspi, xspi->rx_bytes);
cdns_spi_write(xspi, CDNS_SPI_IDR, cdns_spi_write(xspi, CDNS_SPI_IDR,
CDNS_SPI_IXR_DEFAULT); CDNS_SPI_IXR_DEFAULT);
spi_finalize_current_transfer(ctlr); spi_finalize_current_transfer(ctlr);
@ -456,10 +444,10 @@ static int cdns_transfer_one(struct spi_controller *ctlr,
/* Set TX empty threshold to half of FIFO depth /* Set TX empty threshold to half of FIFO depth
* only if TX bytes are more than half FIFO depth. * only if TX bytes are more than half FIFO depth.
*/ */
if (xspi->tx_bytes > (xspi->tx_fifo_depth >> 1)) if (xspi->tx_bytes > xspi->tx_fifo_depth)
cdns_spi_write(xspi, CDNS_SPI_THLD, xspi->tx_fifo_depth >> 1); cdns_spi_write(xspi, CDNS_SPI_THLD, xspi->tx_fifo_depth >> 1);
cdns_spi_fill_tx_fifo(xspi); cdns_spi_fill_tx_fifo(xspi, xspi->tx_fifo_depth);
spi_transfer_delay_exec(transfer); spi_transfer_delay_exec(transfer);
cdns_spi_write(xspi, CDNS_SPI_IER, CDNS_SPI_IXR_DEFAULT); cdns_spi_write(xspi, CDNS_SPI_IER, CDNS_SPI_IXR_DEFAULT);