diff mbox series

[net-next,11/14] can: mcp251xfd: rx: prepare to workaround broken RX FIFO head index erratum

Message ID 20240629114017.1080160-12-mkl@pengutronix.de (mailing list archive)
State New
Delegated to: Netdev Maintainers
Headers show
Series [net-next,01/14] can: rcar_canfd: Simplify clock handling | expand

Checks

Context Check Description
netdev/series_format success Pull request is its own cover letter
netdev/tree_selection success Clearly marked for net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 839 this patch: 839
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers warning 4 maintainers not CCed: edumazet@google.com pabeni@redhat.com mailhol.vincent@wanadoo.fr manivannan.sadhasivam@linaro.org
netdev/build_clang success Errors and warnings before: 846 this patch: 846
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 846 this patch: 846
netdev/checkpatch warning WARNING: line length of 92 exceeds 80 columns
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline fail Was 1 now: 2
netdev/contest success net-next-2024-07-01--15-00 (tests: 664)

Commit Message

Marc Kleine-Budde June 29, 2024, 11:36 a.m. UTC 
This is a preparatory patch to work around erratum DS80000789E 6 of
the mcp2518fd, the other variants of the chip family (mcp2517fd and
mcp251863) are probably also affected.

When handling the RX interrupt, the driver iterates over all pending
FIFOs (which are implemented as ring buffers in hardware) and reads
the FIFO header index from the RX FIFO STA register of the chip.

In the bad case, the driver reads a too large head index. In the
original code, the driver always trusted the read value, which caused
old CAN frames that were already processed, or new, incompletely
written CAN frames to be (re-)processed.

Instead of reading and trusting the head index, read the head index
and calculate the number of CAN frames that were supposedly received -
replace mcp251xfd_rx_ring_update() with mcp251xfd_get_rx_len().

The mcp251xfd_handle_rxif_ring() function reads the received CAN
frames from the chip, iterates over them and pushes them into the
network stack. Prepare that the iteration can be stopped if an old CAN
frame is detected. The actual code to detect old or incomplete frames
and abort will be added in the next patch.

Link: https://lore.kernel.org/all/BL3PR11MB64844C1C95CA3BDADAE4D8CCFBC99@BL3PR11MB6484.namprd11.prod.outlook.com
Reported-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Closes: https://lore.kernel.org/all/FR0P281MB1966273C216630B120ABB6E197E89@FR0P281MB1966.DEUP281.PROD.OUTLOOK.COM
Tested-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Tested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 .../net/can/spi/mcp251xfd/mcp251xfd-ring.c    |  2 +
 drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c  | 89 +++++++++++--------
 drivers/net/can/spi/mcp251xfd/mcp251xfd.h     | 12 +--
 3 files changed, 56 insertions(+), 47 deletions(-)
diff mbox series

Patch

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
index bfe4caa0c99d..b308a375e26e 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
@@ -507,6 +507,8 @@  int mcp251xfd_ring_alloc(struct mcp251xfd_priv *priv)
 		}
 
 		rx_ring->obj_num = rx_obj_num;
+		rx_ring->obj_num_shift_to_u8 = BITS_PER_TYPE(rx_ring->obj_num_shift_to_u8) -
+			ilog2(rx_obj_num);
 		rx_ring->obj_size = rx_obj_size;
 		priv->rx[i] = rx_ring;
 	}
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
index 2c2b057b7ac7..a79e6c661ecc 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
@@ -2,7 +2,7 @@ 
 //
 // mcp251xfd - Microchip MCP251xFD Family CAN controller driver
 //
-// Copyright (c) 2019, 2020, 2021 Pengutronix,
+// Copyright (c) 2019, 2020, 2021, 2023 Pengutronix,
 //               Marc Kleine-Budde <kernel@pengutronix.de>
 //
 // Based on:
@@ -16,23 +16,14 @@ 
 
 #include "mcp251xfd.h"
 
-static inline int
-mcp251xfd_rx_head_get_from_chip(const struct mcp251xfd_priv *priv,
-				const struct mcp251xfd_rx_ring *ring,
-				u8 *rx_head, bool *fifo_empty)
+static inline bool mcp251xfd_rx_fifo_sta_empty(const u32 fifo_sta)
 {
-	u32 fifo_sta;
-	int err;
+	return !(fifo_sta & MCP251XFD_REG_FIFOSTA_TFNRFNIF);
+}
 
-	err = regmap_read(priv->map_reg, MCP251XFD_REG_FIFOSTA(ring->fifo_nr),
-			  &fifo_sta);
-	if (err)
-		return err;
-
-	*rx_head = FIELD_GET(MCP251XFD_REG_FIFOSTA_FIFOCI_MASK, fifo_sta);
-	*fifo_empty = !(fifo_sta & MCP251XFD_REG_FIFOSTA_TFNRFNIF);
-
-	return 0;
+static inline bool mcp251xfd_rx_fifo_sta_full(const u32 fifo_sta)
+{
+	return fifo_sta & MCP251XFD_REG_FIFOSTA_TFERFFIF;
 }
 
 static inline int
@@ -80,29 +71,49 @@  mcp251xfd_check_rx_tail(const struct mcp251xfd_priv *priv,
 }
 
 static int
-mcp251xfd_rx_ring_update(const struct mcp251xfd_priv *priv,
-			 struct mcp251xfd_rx_ring *ring)
+mcp251xfd_get_rx_len(const struct mcp251xfd_priv *priv,
+		     const struct mcp251xfd_rx_ring *ring,
+		     u8 *len_p)
 {
-	u32 new_head;
-	u8 chip_rx_head;
-	bool fifo_empty;
+	const u8 shift = ring->obj_num_shift_to_u8;
+	u8 chip_head, tail, len;
+	u32 fifo_sta;
 	int err;
 
-	err = mcp251xfd_rx_head_get_from_chip(priv, ring, &chip_rx_head,
-					      &fifo_empty);
-	if (err || fifo_empty)
+	err = regmap_read(priv->map_reg, MCP251XFD_REG_FIFOSTA(ring->fifo_nr),
+			  &fifo_sta);
+	if (err)
 		return err;
 
-	/* chip_rx_head, is the next RX-Object filled by the HW.
-	 * The new RX head must be >= the old head.
+	if (mcp251xfd_rx_fifo_sta_empty(fifo_sta)) {
+		*len_p = 0;
+		return 0;
+	}
+
+	if (mcp251xfd_rx_fifo_sta_full(fifo_sta)) {
+		*len_p = ring->obj_num;
+		return 0;
+	}
+
+	chip_head = FIELD_GET(MCP251XFD_REG_FIFOSTA_FIFOCI_MASK, fifo_sta);
+
+	err =  mcp251xfd_check_rx_tail(priv, ring);
+	if (err)
+		return err;
+	tail = mcp251xfd_get_rx_tail(ring);
+
+	/* First shift to full u8. The subtraction works on signed
+	 * values, that keeps the difference steady around the u8
+	 * overflow. The right shift acts on len, which is an u8.
 	 */
-	new_head = round_down(ring->head, ring->obj_num) + chip_rx_head;
-	if (new_head <= ring->head)
-		new_head += ring->obj_num;
+	BUILD_BUG_ON(sizeof(ring->obj_num) != sizeof(chip_head));
+	BUILD_BUG_ON(sizeof(ring->obj_num) != sizeof(tail));
+	BUILD_BUG_ON(sizeof(ring->obj_num) != sizeof(len));
 
-	ring->head = new_head;
+	len = (chip_head << shift) - (tail << shift);
+	*len_p = len >> shift;
 
-	return mcp251xfd_check_rx_tail(priv, ring);
+	return 0;
 }
 
 static void
@@ -208,6 +219,8 @@  mcp251xfd_handle_rxif_ring_uinc(const struct mcp251xfd_priv *priv,
 	if (!len)
 		return 0;
 
+	ring->head += len;
+
 	/* Increment the RX FIFO tail pointer 'len' times in a
 	 * single SPI message.
 	 *
@@ -233,22 +246,22 @@  mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 			   struct mcp251xfd_rx_ring *ring)
 {
 	struct mcp251xfd_hw_rx_obj_canfd *hw_rx_obj = ring->obj;
-	u8 rx_tail, len;
+	u8 rx_tail, len, l;
 	int err, i;
 
-	err = mcp251xfd_rx_ring_update(priv, ring);
+	err = mcp251xfd_get_rx_len(priv, ring, &len);
 	if (err)
 		return err;
 
-	while ((len = mcp251xfd_get_rx_linear_len(ring))) {
+	while ((l = mcp251xfd_get_rx_linear_len(ring, len))) {
 		rx_tail = mcp251xfd_get_rx_tail(ring);
 
 		err = mcp251xfd_rx_obj_read(priv, ring, hw_rx_obj,
-					    rx_tail, len);
+					    rx_tail, l);
 		if (err)
 			return err;
 
-		for (i = 0; i < len; i++) {
+		for (i = 0; i < l; i++) {
 			err = mcp251xfd_handle_rxif_one(priv, ring,
 							(void *)hw_rx_obj +
 							i * ring->obj_size);
@@ -256,9 +269,11 @@  mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 				return err;
 		}
 
-		err = mcp251xfd_handle_rxif_ring_uinc(priv, ring, len);
+		err = mcp251xfd_handle_rxif_ring_uinc(priv, ring, l);
 		if (err)
 			return err;
+
+		len -= l;
 	}
 
 	return 0;
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
index 4d31689d73c8..453a2b193c75 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
@@ -556,6 +556,7 @@  struct mcp251xfd_rx_ring {
 	u8 nr;
 	u8 fifo_nr;
 	u8 obj_num;
+	u8 obj_num_shift_to_u8;
 	u8 obj_size;
 
 	union mcp251xfd_write_reg_buf irq_enable_buf;
@@ -931,18 +932,9 @@  static inline u8 mcp251xfd_get_rx_tail(const struct mcp251xfd_rx_ring *ring)
 	return ring->tail & (ring->obj_num - 1);
 }
 
-static inline u8 mcp251xfd_get_rx_len(const struct mcp251xfd_rx_ring *ring)
-{
-	return ring->head - ring->tail;
-}
-
 static inline u8
-mcp251xfd_get_rx_linear_len(const struct mcp251xfd_rx_ring *ring)
+mcp251xfd_get_rx_linear_len(const struct mcp251xfd_rx_ring *ring, u8 len)
 {
-	u8 len;
-
-	len = mcp251xfd_get_rx_len(ring);
-
 	return min_t(u8, len, ring->obj_num - mcp251xfd_get_rx_tail(ring));
 }