gpio: pca953x: hack to fix 24 bit gpio expanders

[ Upstream commit 3b00691c ]

24 bit expanders use REG_ADDR_AI in combination with register addressing. This
conflicts with regmap which takes this bit as part of the register number,
i.e. a second cache entry is defined for accessed with REG_ADDR_AI being
set although on the chip it is the same register as with REG_ADDR_AI being
cleared.

The problem was introduced by

	commit b32cecb4 ("gpio: pca953x: Extract the register address mangling to single function")

but only became visible by

	commit 8b9f9d4d ("regmap: verify if register is writeable before writing operations")

because before, the regmap size was effectively ignored and
pca953x_writeable_register() did know to ignore REG_ADDR_AI. Still, there
were two separate cache entries created.

Since the use of REG_ADDR_AI seems to be static we can work around this
issue by simply increasing the size of the regmap to cover the "virtual"
registers with REG_ADDR_AI being set. This only means that half of the
regmap buffer will be unused.
Reported-by: H. Nikolaus Schaller <hns@goldelico.com>
Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/gpio/gpio-pca953x.c

@@ -306,7 +306,8 @@ static const struct regmap_config pca953x_i2c_regmap = {
 	.volatile_reg = pca953x_volatile_register,
 
 	.cache_type = REGCACHE_RBTREE,
-	.max_register = 0x7f,
+	/* REVISIT: should be 0x7f but some 24 bit chips use REG_ADDR_AI */
+	.max_register = 0xff,
 };
 
 static u8 pca953x_recalc_addr(struct pca953x_chip *chip, int reg, int off,