[PATCH v3 5/8] can: mcp251xfd: add workaround for errata 5

[Gregor Herburger <gregor.herburger@xxxxxxxxxxxxxxx>]

According to Errata DS80000789E 5 writing IOCON register using one SPI
write command clears LAT0/LAT1.

Errata Fix/Work Around suggests to write registers with single byte write
instructions. However, it seems that every write to the second byte
causes the overwrite of LAT0/LAT1.

Never write byte 2 of IOCON register to avoid clearing of LAT0/LAT1.

Signed-off-by: Gregor Herburger <gregor.herburger@xxxxxxxxxxxxxxx>
---
 drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c | 89 ++++++++++++++++++++++--
 1 file changed, 83 insertions(+), 6 deletions(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
index 52716cce73ec..8499a303ad77 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
@@ -13,9 +13,9 @@
 static const struct regmap_config mcp251xfd_regmap_crc;
 
 static int
-mcp251xfd_regmap_nocrc_gather_write(void *context,
-				    const void *reg, size_t reg_len,
-				    const void *val, size_t val_len)
+_mcp251xfd_regmap_nocrc_gather_write(void *context,
+				     const void *reg, size_t reg_len,
+				     const void *val, size_t val_len)
 {
 	struct spi_device *spi = context;
 	struct mcp251xfd_priv *priv = spi_get_drvdata(spi);
@@ -39,6 +39,45 @@ mcp251xfd_regmap_nocrc_gather_write(void *context,
 	return spi_sync_transfer(spi, xfer, ARRAY_SIZE(xfer));
 }
 
+static int
+mcp251xfd_regmap_nocrc_gather_write(void *context,
+				    const void *reg_p, size_t reg_len,
+				    const void *val, size_t val_len)
+{
+	const u16 byte_exclude = MCP251XFD_REG_IOCON +
+				 mcp251xfd_first_byte_set(MCP251XFD_REG_IOCON_GPIO_MASK);
+	u16 reg = be16_to_cpu(*(u16 *)reg_p) & MCP251XFD_SPI_ADDRESS_MASK;
+	int ret;
+
+	/* Never write to bits 16..23 of IOCON register to avoid clearing of LAT0/LAT1
+	 *
+	 * According to MCP2518FD Errata DS80000789E 5 writing IOCON register using one
+	 * SPI write command clears LAT0/LAT1.
+	 *
+	 * Errata Fix/Work Around suggests to write registers with single byte
+	 * write instructions. However, it seems that the byte at 0xe06(IOCON[23:16])
+	 * is for read-only access and writing to it causes the clearing of LAT0/LAT1.
+	 */
+	if (reg <= byte_exclude && reg + val_len > byte_exclude) {
+		size_t len = byte_exclude - reg;
+
+		/* Write up to 0xe05 */
+		ret = _mcp251xfd_regmap_nocrc_gather_write(context, reg_p, reg_len, val, len);
+		if (ret)
+			return ret;
+
+		/* Write from 0xe07 on */
+		reg += len + 1;
+		reg = cpu_to_be16(MCP251XFD_SPI_INSTRUCTION_WRITE | reg);
+		return _mcp251xfd_regmap_nocrc_gather_write(context, &reg, reg_len,
+							    val + len + 1,
+							    val_len - len - 1);
+	}
+
+	return _mcp251xfd_regmap_nocrc_gather_write(context, reg_p, reg_len,
+						  val, val_len);
+}
+
 static int
 mcp251xfd_regmap_nocrc_write(void *context, const void *data, size_t count)
 {
@@ -197,9 +236,9 @@ mcp251xfd_regmap_nocrc_read(void *context,
 }
 
 static int
-mcp251xfd_regmap_crc_gather_write(void *context,
-				  const void *reg_p, size_t reg_len,
-				  const void *val, size_t val_len)
+_mcp251xfd_regmap_crc_gather_write(void *context,
+				   const void *reg_p, size_t reg_len,
+				   const void *val, size_t val_len)
 {
 	struct spi_device *spi = context;
 	struct mcp251xfd_priv *priv = spi_get_drvdata(spi);
@@ -230,6 +269,44 @@ mcp251xfd_regmap_crc_gather_write(void *context,
 	return spi_sync_transfer(spi, xfer, ARRAY_SIZE(xfer));
 }
 
+static int
+mcp251xfd_regmap_crc_gather_write(void *context,
+				  const void *reg_p, size_t reg_len,
+				  const void *val, size_t val_len)
+{
+	const u16 byte_exclude = MCP251XFD_REG_IOCON +
+				 mcp251xfd_first_byte_set(MCP251XFD_REG_IOCON_GPIO_MASK);
+	u16 reg = *(u16 *)reg_p;
+	int ret;
+
+	/* Never write to bits 16..23 of IOCON register to avoid clearing of LAT0/LAT1
+	 *
+	 * According to MCP2518FD Errata DS80000789E 5 writing IOCON register using one
+	 * SPI write command clears LAT0/LAT1.
+	 *
+	 * Errata Fix/Work Around suggests to write registers with single byte
+	 * write instructions. However, it seems that the byte at 0xe06(IOCON[23:16])
+	 * is for read-only access and writing to it causes the clearing of LAT0/LAT1.
+	 */
+	if (reg <= byte_exclude  && reg + val_len > byte_exclude) {
+		size_t len = byte_exclude - reg;
+
+		/* Write up to 0xe05 */
+		ret = _mcp251xfd_regmap_crc_gather_write(context, &reg, reg_len, val, len);
+		if (ret)
+			return ret;
+
+		/* Write from 0xe07 on */
+		reg += len + 1;
+		return _mcp251xfd_regmap_crc_gather_write(context, &reg, reg_len,
+							  val + len + 1,
+							  val_len - len - 1);
+	}
+
+	return _mcp251xfd_regmap_crc_gather_write(context, reg_p, reg_len,
+						  val, val_len);
+}
+
 static int
 mcp251xfd_regmap_crc_write(void *context,
 			   const void *data, size_t count)

-- 
2.34.1