can: mcp251xfd: __mcp251xfd_chip_set_mode(): increase poll timeout

The mcp251xfd controller needs an idle bus to enter 'Normal CAN 2.0
mode' or . The maximum length of a CAN frame is 736 bits (64 data
bytes, CAN-FD, EFF mode, worst case bit stuffing and interframe
spacing). For low bit rates like 10 kbit/s the arbitrarily chosen
MCP251XFD_POLL_TIMEOUT_US of 1 ms is too small.

Otherwise during polling for the CAN controller to enter 'Normal CAN
2.0 mode' the timeout limit is exceeded and the configuration fails
with:

| $ ip link set dev can1 up type can bitrate 10000
| [  731.911072] mcp251xfd spi2.1 can1: Controller failed to enter mode CAN 2.0 Mode (6) and stays in Configuration Mode (4) (con=0x068b0760, osc=0x00000468).
| [  731.927192] mcp251xfd spi2.1 can1: CRC read error at address 0x0e0c (length=4, data=00 00 00 00, CRC=0x0000) retrying.
| [  731.938101] A link change request failed with some changes committed already. Interface can1 may have been left with an inconsistent configuration, please check.
| RTNETLINK answers: Connection timed out

Make MCP251XFD_POLL_TIMEOUT_US timeout calculation dynamic. Use
maximum of 1ms and bit time of 1 full 64 data bytes CAN-FD frame in
EFF mode, worst case bit stuffing and interframe spacing at the
current bit rate.

For easier backporting define the macro MCP251XFD_FRAME_LEN_MAX_BITS
that holds the max frame length in bits, which is 736. This can be
replaced by can_frame_bits(true, true, true, true, CANFD_MAX_DLEN) in
a cleanup patch later.

Fixes: 55e5b97f00 ("can: mcp25xxfd: add driver for Microchip MCP25xxFD SPI CAN")
Signed-off-by: Fedor Ross <fedor.ross@ifm.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20230717-mcp251xfd-fix-increase-poll-timeout-v5-1-06600f34c684@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -227,6 +227,8 @@ static int
 __mcp251xfd_chip_set_mode(const struct mcp251xfd_priv *priv,
 			  const u8 mode_req, bool nowait)
 {
+	const struct can_bittiming *bt = &priv->can.bittiming;
+	unsigned long timeout_us = MCP251XFD_POLL_TIMEOUT_US;
 	u32 con = 0, con_reqop, osc = 0;
 	u8 mode;
 	int err;
@@ -246,12 +248,16 @@ __mcp251xfd_chip_set_mode(const struct mcp251xfd_priv *priv,
 	if (mode_req == MCP251XFD_REG_CON_MODE_SLEEP || nowait)
 		return 0;
 
+	if (bt->bitrate)
+		timeout_us = max_t(unsigned long, timeout_us,
+				   MCP251XFD_FRAME_LEN_MAX_BITS * USEC_PER_SEC /
+				   bt->bitrate);
+
 	err = regmap_read_poll_timeout(priv->map_reg, MCP251XFD_REG_CON, con,
 				       !mcp251xfd_reg_invalid(con) &&
 				       FIELD_GET(MCP251XFD_REG_CON_OPMOD_MASK,
 						 con) == mode_req,
-				       MCP251XFD_POLL_SLEEP_US,
-				       MCP251XFD_POLL_TIMEOUT_US);
+				       MCP251XFD_POLL_SLEEP_US, timeout_us);
 	if (err != -ETIMEDOUT && err != -EBADMSG)
 		return err;
 

drivers/net/can/spi/mcp251xfd/mcp251xfd.h

@@ -387,6 +387,7 @@ static_assert(MCP251XFD_TIMESTAMP_WORK_DELAY_SEC <
 #define MCP251XFD_OSC_STAB_TIMEOUT_US (10 * MCP251XFD_OSC_STAB_SLEEP_US)
 #define MCP251XFD_POLL_SLEEP_US (10)
 #define MCP251XFD_POLL_TIMEOUT_US (USEC_PER_MSEC)
+#define MCP251XFD_FRAME_LEN_MAX_BITS (736)
 
 /* Misc */
 #define MCP251XFD_NAPI_WEIGHT 32