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Date:   Tue, 20 Jun 2023 14:22:15 -0700
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Subject: Re: [PATCH 1/1] regmap: spi-avmm: Fix regmap_bus max_raw_write
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To:     <broonie@kernel.org>, <gregkh@linuxfoundation.org>,
        <rafael@kernel.org>, <linux-kernel@vger.kernel.org>
CC:     <yilun.xu@intel.com>, <matthew.gerlach@linux.intel.com>
References: <20230620202824.380313-1-russell.h.weight@intel.com>
From:   Russ Weight <russell.h.weight@intel.com>
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On 6/20/23 13:28, Russ Weight wrote:
> The max_raw_write member of the regmap_spi_avmm_bus structure is defined
> as:
> 	.max_raw_write = SPI_AVMM_VAL_SIZE * MAX_WRITE_CNT
>
> SPI_AVMM_VAL_SIZE == 4 and MAX_WRITE_CNT == 1 so this results in a
> maximum write transfer size of 4 bytes which provides only enough space to
> transfer the address of the target register. It provides no space for the
> value to be transferred. This bug became an issue (divide-by-zero in
> _regmap_raw_write()) after the following was accepted into mainline:
>
> commit 3981514180c9 ("regmap: Account for register length when chunking")
>
> Change max_raw_write to include space (4 additional bytes) for both the
> register address and value:
>
> 	.max_raw_write = SPI_AVMM_REG_SIZE + SPI_AVMM_VAL_SIZE * MAX_WRITE_CNT
>
> Fixes: 7f9fb67358a2 ("regmap: add Intel SPI Slave to AVMM Bus Bridge support")
> Reviewed-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
> Signed-off-by: Russ Weight <russell.h.weight@intel.com>

Cc: stable@vger.kernel.org
> ---
>  drivers/base/regmap/regmap-spi-avmm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/base/regmap/regmap-spi-avmm.c b/drivers/base/regmap/regmap-spi-avmm.c
> index 4c2b94b3e30b..6af692844c19 100644
> --- a/drivers/base/regmap/regmap-spi-avmm.c
> +++ b/drivers/base/regmap/regmap-spi-avmm.c
> @@ -660,7 +660,7 @@ static const struct regmap_bus regmap_spi_avmm_bus = {
>  	.reg_format_endian_default = REGMAP_ENDIAN_NATIVE,
>  	.val_format_endian_default = REGMAP_ENDIAN_NATIVE,
>  	.max_raw_read = SPI_AVMM_VAL_SIZE * MAX_READ_CNT,
> -	.max_raw_write = SPI_AVMM_VAL_SIZE * MAX_WRITE_CNT,
> +	.max_raw_write = SPI_AVMM_REG_SIZE + SPI_AVMM_VAL_SIZE * MAX_WRITE_CNT,
>  	.free_context = spi_avmm_bridge_ctx_free,
>  };
>