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From:   Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
To:     broonie@kernel.org
Cc:     srivasam@codeaurora.org, rafael@kernel.org,
        dp@opensource.wolfsonmicro.com, linux-kernel@vger.kernel.org,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        stable@vger.kernel.org, Marek Szyprowski <m.szyprowski@samsung.com>
Subject: [PATCH] regmap: move readable check before accessing regcache.
Date:   Fri, 18 Jun 2021 12:35:58 +0100
Message-Id: <20210618113558.10046-1-srinivas.kandagatla@linaro.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The issue that I encountered is when doing regmap_update_bits on
a write only register. In regcache path this will not do the right
thing as the register is not readable and driver which is using
regmap_update_bits will never notice that it can not do a update
bits on write only register leading to inconsistent writes and
random hardware behavior.

There seems to be missing checks in regcache_read() which is
now added by moving the orignal check in _regmap_read() before
accessing regcache.

Cc: stable@vger.kernel.org
Fixes: 5d1729e7f02f ("regmap: Incorporate the regcache core into regmap")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
---
 drivers/base/regmap/regmap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 297e95be25b3..3ed37a09a8e9 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -2677,6 +2677,9 @@ static int _regmap_read(struct regmap *map, unsigned int reg,
 	int ret;
 	void *context = _regmap_map_get_context(map);
 
+	if (!regmap_readable(map, reg))
+		return -EIO;
+
 	if (!map->cache_bypass) {
 		ret = regcache_read(map, reg, val);
 		if (ret == 0)
@@ -2686,9 +2689,6 @@ static int _regmap_read(struct regmap *map, unsigned int reg,
 	if (map->cache_only)
 		return -EBUSY;
 
-	if (!regmap_readable(map, reg))
-		return -EIO;
-
 	ret = map->reg_read(context, reg, val);
 	if (ret == 0) {
 		if (regmap_should_log(map))
-- 
2.21.0