linux-kernel - [PATCH] regmap: mmio: Allow passing an empty config->reg

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Message-Id: <20230511142735.316445-1-maxime.chevallier@bootlin.com>
Date:   Thu, 11 May 2023 16:27:35 +0200
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Colin Foster <colin.foster@...advantage.com>
Cc:     Maxime Chevallier <maxime.chevallier@...tlin.com>,
        linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
        alexis.lothore@...tlin.com
Subject: [PATCH] regmap: mmio: Allow passing an empty config->reg_stride

Regmap's stride is used for MMIO regmaps to check the correctness of
reg_width. However, it's acceptable to pass an empty config->reg_stride,
in that case the actual stride used is 1.

There are valid cases now to pass an empty stride, when using
down/upshifting of register address. In this case, the stride value
loses its sense, so ignore the reg_width when the stride isn't set.

Signed-off-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
---
This patch is a followup on the discussion here [1]. The regmap core
actually supports pretty-well not passing a stride, and uses a value of
1 by default. However regmap-mmio has specific checks for that case,
which is the only place such a check needs to be added.

[1] : https://lore.kernel.org/all/20230420150617.381922-1-maxime.chevallier@bootlin.com/

 drivers/base/regmap/regmap-mmio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regmap-mmio.c b/drivers/base/regmap/regmap-mmio.c
index 3ccdd86a97e7..8132b5c101c4 100644
--- a/drivers/base/regmap/regmap-mmio.c
+++ b/drivers/base/regmap/regmap-mmio.c
@@ -448,7 +448,7 @@ static struct regmap_mmio_context *regmap_mmio_gen_context(struct device *dev,
 	if (min_stride < 0)
 		return ERR_PTR(min_stride);
 
-	if (config->reg_stride < min_stride)
+	if (config->reg_stride && config->reg_stride < min_stride)
 		return ERR_PTR(-EINVAL);
 
 	if (config->use_relaxed_mmio && config->io_port)
-- 
2.40.1