This is a note to let you know that I've just added the patch titled
spi: microchip-core: defer asserting chip select until just before write to TX FIFO
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
spi-microchip-core-defer-asserting-chip-select-until.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 04a8f0db32f200bcb777681f28f0c75e33a0f367
Author: Steve Wilkins <steve.wilkins@xxxxxxxxxxxxx>
Date: Mon Jul 15 12:13:53 2024 +0100
spi: microchip-core: defer asserting chip select until just before write to TX FIFO
[ Upstream commit 22fd98c107c792e35db7abe45298bc3a29bf4723 ]
Setting up many of the registers for a new SPI transfer requires the
SPI controller to be disabled after set_cs() has been called to assert
the chip select line. However, disabling the controller results in the
SCLK and MOSI output pins being tristate, which can cause clock
transitions to be seen by a slave device whilst SS is active. To fix
this, the CS is only set to inactive inline, whilst setting it active
is deferred until all registers are set up and the any controller
disables have been completed.
Fixes: 9ac8d17694b6 ("spi: add support for microchip fpga spi controllers")
Signed-off-by: Steve Wilkins <steve.wilkins@xxxxxxxxxxxxx>
Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20240715-sanitizer-recant-dd96b7a97048@wendy
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/spi/spi-microchip-core.c b/drivers/spi/spi-microchip-core.c
index 1a19701cc6118..b49843f0c2e8e 100644
--- a/drivers/spi/spi-microchip-core.c
+++ b/drivers/spi/spi-microchip-core.c
@@ -103,6 +103,7 @@ struct mchp_corespi {
u8 *rx_buf;
u32 clk_gen; /* divider for spi output clock generated by the controller */
u32 clk_mode;
+ u32 pending_slave_select;
int irq;
int tx_len;
int rx_len;
@@ -249,8 +250,18 @@ static void mchp_corespi_set_cs(struct spi_device *spi, bool disable)
reg = mchp_corespi_read(corespi, REG_SLAVE_SELECT);
reg &= ~BIT(spi_get_chipselect(spi, 0));
reg |= !disable << spi_get_chipselect(spi, 0);
+ corespi->pending_slave_select = reg;
- mchp_corespi_write(corespi, REG_SLAVE_SELECT, reg);
+ /*
+ * Only deassert chip select immediately. Writing to some registers
+ * requires the controller to be disabled, which results in the
+ * output pins being tristated and can cause the SCLK and MOSI lines
+ * to transition. Therefore asserting the chip select is deferred
+ * until just before writing to the TX FIFO, to ensure the device
+ * doesn't see any spurious clock transitions whilst CS is enabled.
+ */
+ if (((spi->mode & SPI_CS_HIGH) == 0) == disable)
+ mchp_corespi_write(corespi, REG_SLAVE_SELECT, reg);
}
static int mchp_corespi_setup(struct spi_device *spi)
@@ -266,6 +277,7 @@ static int mchp_corespi_setup(struct spi_device *spi)
if (spi->mode & SPI_CS_HIGH) {
reg = mchp_corespi_read(corespi, REG_SLAVE_SELECT);
reg |= BIT(spi_get_chipselect(spi, 0));
+ corespi->pending_slave_select = reg;
mchp_corespi_write(corespi, REG_SLAVE_SELECT, reg);
}
return 0;
@@ -307,7 +319,8 @@ static void mchp_corespi_init(struct spi_master *master, struct mchp_corespi *sp
* select is relinquished to the hardware. SSELOUT is enabled too so we
* can deal with active high slaves.
*/
- mchp_corespi_write(spi, REG_SLAVE_SELECT, SSELOUT | SSEL_DIRECT);
+ spi->pending_slave_select = SSELOUT | SSEL_DIRECT;
+ mchp_corespi_write(spi, REG_SLAVE_SELECT, spi->pending_slave_select);
control = mchp_corespi_read(spi, REG_CONTROL);
@@ -476,6 +489,8 @@ static int mchp_corespi_transfer_one(struct spi_master *master,
mchp_corespi_set_xfer_size(spi, (spi->tx_len > FIFO_DEPTH)
? FIFO_DEPTH : spi->tx_len);
+ mchp_corespi_write(spi, REG_SLAVE_SELECT, spi->pending_slave_select);
+
while (spi->tx_len)
mchp_corespi_write_fifo(spi);
