linux-kernel - Re: [PATCH v2 4/6] can: mcp251xfd: mcp251xfd_regmap_crc

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Message-ID: <20240506-aromatic-dainty-orangutan-f8b57c-mkl@pengutronix.de>
Date: Mon, 6 May 2024 11:18:55 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Gregor Herburger <gregor.herburger@...tq-group.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
	Thomas Kopp <thomas.kopp@...rochip.com>, Vincent Mailhol <mailhol.vincent@...adoo.fr>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, linux-can@...r.kernel.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux@...tq-group.com
Subject: Re: [PATCH v2 4/6] can: mcp251xfd: mcp251xfd_regmap_crc_write():
 workaround for errata 5

On 06.05.2024 07:59:46, Gregor Herburger wrote:
> 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@...tq-group.com>
> ---
>  drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c | 29 +++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
> index 65150e762007..43fcf7f50591 100644
> --- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
> +++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
> @@ -229,14 +229,41 @@ mcp251xfd_regmap_crc_gather_write(void *context,
>  	return spi_sync_transfer(spi, xfer, ARRAY_SIZE(xfer));
>  }
>  
> +static int mcp251xfd_regmap_crc_write_iocon(void *context, const void *data)
> +{
> +	u16 reg = MCP251XFD_REG_IOCON;

const

> +
> +	/* Never write to bits 16..23 of IOCON register to avoid clearing of LAT0/LAT1
> +	 *
> +	 * According to Errata DS80000789E 5 writing IOCON register using one

Just for completeness add "mcp2518fd" in front of Errata.

> +	 * 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.
> +	 */
> +
> +	/* Write IOCON[15:0] */
> +	mcp251xfd_regmap_crc_gather_write(context, &reg, 1, data, 2);
> +	reg += 3;
> +	/* Write IOCON[31:24] */
> +	mcp251xfd_regmap_crc_gather_write(context, &reg, 1, data + 3, 1);

Please add error handling.

> +
> +	return 0;
> +}
> +
>  static int
>  mcp251xfd_regmap_crc_write(void *context,
>  			   const void *data, size_t count)
>  {
>  	const size_t data_offset = sizeof(__be16) +
>  		mcp251xfd_regmap_crc.pad_bits / BITS_PER_BYTE;
> +	u16 reg = *(u16 *)data;
>  
> -	return mcp251xfd_regmap_crc_gather_write(context,
> +	if (reg == MCP251XFD_REG_IOCON)
> +		return mcp251xfd_regmap_crc_write_iocon(context, data + data_offset);

Please also check that "count" is sizeof(__le32).

> +	else
> +		return mcp251xfd_regmap_crc_gather_write(context,
>  						 data, data_offset,
>  						 data + data_offset,
>  						 count - data_offset);
> 

Also add the workaround for the nocrc regmap.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
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