Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Russ Weight <russell.h.weight@intel.com>
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,
        Russ Weight <russell.h.weight@intel.com>
Subject: [PATCH 1/1] regmap: spi-avmm: Fix regmap_bus max_raw_write
Date:   Tue, 20 Jun 2023 13:28:24 -0700
Message-Id: <20230620202824.380313-1-russell.h.weight@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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>
---
 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,
 };
 
-- 
2.25.1