[PATCH 1/3] spi: xilinx: Detect stall with Unknown commands

[Ricardo Ribalda Delgado <ricardo.ribalda-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

When the core is configured in C_SPI_MODE > 0, it integrates a
lookup table that automatically configures the core in dual or quad mode
based on the command (first byte on the tx fifo).

Unfortunately, that list mode_?_memoy_*.mif does not contain all the
supported commands by the flash.

Since 4.14 spi-nor automatically tries to probe the flash using SFDP
(command 0x5a), and that command is not part of the list_mode table.

Whit the right combination of C_SPI_MODE and C_SPI_MEMORY this leads
into a stall that can only be recovered with a soft rest.

This patch detects this kind of stall and returns -EIO to the caller on
those commands. spi-nor can handle this error properly:

m25p80 spi0.0: Detected stall. Check C_SPI_MODE and C_SPI_MEMORY. 0x21 0x2404
m25p80 spi0.0: SPI transfer failed: -5
spi_master spi0: failed to transfer one message from queue
m25p80 spi0.0: s25sl064p (8192 Kbytes)

Cc: Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 drivers/spi/spi-xilinx.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/spi/spi-xilinx.c b/drivers/spi/spi-xilinx.c
index bc7100b93dfc..e0b9fe1d0e37 100644
--- a/drivers/spi/spi-xilinx.c
+++ b/drivers/spi/spi-xilinx.c
@@ -271,6 +271,7 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
 	while (remaining_words) {
 		int n_words, tx_words, rx_words;
 		u32 sr;
+		int stalled;
 
 		n_words = min(remaining_words, xspi->buffer_size);
 
@@ -299,7 +300,17 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
 
 		/* Read out all the data from the Rx FIFO */
 		rx_words = n_words;
+		stalled = 10;
 		while (rx_words) {
+			if (rx_words == n_words && !(stalled--) &&
+			    !(sr & XSPI_SR_TX_EMPTY_MASK) &&
+			    (sr & XSPI_SR_RX_EMPTY_MASK)) {
+				dev_err(&spi->dev,
+					"Detected stall. Check C_SPI_MODE and C_SPI_MEMORY\n");
+				xspi_init_hw(xspi);
+				return -EIO;
+			}
+
 			if ((sr & XSPI_SR_TX_EMPTY_MASK) && (rx_words > 1)) {
 				xilinx_spi_rx(xspi);
 				rx_words--;
-- 
2.15.0

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