In order to optimize FIFO access, especially on m_can cores attached to slow busses like SPI, in patch

| e39381770ec9 ("can: m_can: Disable IRQs on FIFO bus errors")

bulk read/write support has been added to the m_can_fifo_{read,write} functions.

That change leads to the tcan driver to call regmap_bulk_{read,write}() with a length of 0 (for CAN frames with 0 data length). regmap treats this as an error:

| tcan4x5x spi1.0 tcan4x5x0: FIFO write returned -22

This patch fixes the problem by not calling the cdev->ops->{read,write)_fifo() in case of a 0 length read/write.

Fixes: e39381770ec9 ("can: m_can: Disable IRQs on FIFO bus errors") Link: https://lore.kernel.org/all/20220114153130.2647738-1-mkl@pengutronix.de Cc: stable@vger.kernel.org Cc: Matt Kline matt@bitbashing.io Cc: Chandrasekar Ramakrishnan rcsekar@samsung.com Reported-by: Michael Anochin anochin@photo-meter.com Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- drivers/net/can/m_can/m_can.c | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c index 5b47cd867783..1a4b56f6fa8c 100644 --- a/drivers/net/can/m_can/m_can.c +++ b/drivers/net/can/m_can/m_can.c @@ -336,6 +336,9 @@ m_can_fifo_read(struct m_can_classdev *cdev, u32 addr_offset = cdev->mcfg[MRAM_RXF0].off + fgi * RXF0_ELEMENT_SIZE + offset;

+ if (val_count == 0) + return 0; + return cdev->ops->read_fifo(cdev, addr_offset, val, val_count); }

@@ -346,6 +349,9 @@ m_can_fifo_write(struct m_can_classdev *cdev, u32 addr_offset = cdev->mcfg[MRAM_TXB].off + fpi * TXB_ELEMENT_SIZE + offset;

+ if (val_count == 0) + return 0; + return cdev->ops->write_fifo(cdev, addr_offset, val, val_count); }