[PATCH 6.1 51/98] can: mcp251xfd: mcp251xfd_ring_alloc(): fix coalescing configuration when switching CAN modes

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Marc Kleine-Budde <mkl@pengutronix.de>

commit eb9a839b3d8a989be5970035a5cf29bcd6ffd24d upstream.

Since commit 50ea5449c563 ("can: mcp251xfd: fix ring configuration
when switching from CAN-CC to CAN-FD mode"), the current ring and
coalescing configuration is passed to can_ram_get_layout(). That fixed
the issue when switching between CAN-CC and CAN-FD mode with
configured ring (rx, tx) and/or coalescing parameters (rx-frames-irq,
tx-frames-irq).

However 50ea5449c563 ("can: mcp251xfd: fix ring configuration when
switching from CAN-CC to CAN-FD mode"), introduced a regression when
switching CAN modes with disabled coalescing configuration: Even if
the previous CAN mode has no coalescing configured, the new mode is
configured with active coalescing. This leads to delayed receiving of
CAN-FD frames.

This comes from the fact, that ethtool uses usecs = 0 and max_frames =
1 to disable coalescing, however the driver uses internally
priv->{rx,tx}_obj_num_coalesce_irq = 0 to indicate disabled
coalescing.

Fix the regression by assigning struct ethtool_coalesce
ec->{rx,tx}_max_coalesced_frames_irq = 1 if coalescing is disabled in
the driver as can_ram_get_layout() expects this.

Reported-by: https://github.com/vdh-robothania
Closes: https://github.com/raspberrypi/linux/issues/6407
Fixes: 50ea5449c563 ("can: mcp251xfd: fix ring configuration when switching from CAN-CC to CAN-FD mode")
Cc: stable@vger.kernel.org
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241025-mcp251xfd-fix-coalesing-v1-1-9d11416de1df@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
@@ -2,7 +2,7 @@
 //
 // mcp251xfd - Microchip MCP251xFD Family CAN controller driver
 //
-// Copyright (c) 2019, 2020, 2021 Pengutronix,
+// Copyright (c) 2019, 2020, 2021, 2024 Pengutronix,
 //               Marc Kleine-Budde <kernel@pengutronix.de>
 //
 // Based on:
@@ -473,9 +473,11 @@ int mcp251xfd_ring_alloc(struct mcp251xf
 		};
 		const struct ethtool_coalesce ec = {
 			.rx_coalesce_usecs_irq = priv->rx_coalesce_usecs_irq,
-			.rx_max_coalesced_frames_irq = priv->rx_obj_num_coalesce_irq,
+			.rx_max_coalesced_frames_irq = priv->rx_obj_num_coalesce_irq == 0 ?
+				1 : priv->rx_obj_num_coalesce_irq,
 			.tx_coalesce_usecs_irq = priv->tx_coalesce_usecs_irq,
-			.tx_max_coalesced_frames_irq = priv->tx_obj_num_coalesce_irq,
+			.tx_max_coalesced_frames_irq = priv->tx_obj_num_coalesce_irq == 0 ?
+				1 : priv->tx_obj_num_coalesce_irq,
 		};
 		struct can_ram_layout layout;