[PATCH v3 2/2] regmap: spi: Check raw_[read|write] against max message size

[Lucas Tanure <tanureal@opensource.cirrus.com>]

regmap-spi will split data and address between two transfers
in the same message, so max_[read|write] must include space
for the address and padding

Signed-off-by: Lucas Tanure <tanureal@opensource.cirrus.com>
---

Changes v3:
New series

 drivers/base/regmap/regmap-spi.c |  4 ++++
 drivers/base/regmap/regmap.c     | 15 +++++++++++++++
 include/linux/regmap.h           |  3 +++
 3 files changed, 22 insertions(+)

diff --git a/drivers/base/regmap/regmap-spi.c b/drivers/base/regmap/regmap-spi.c
index 0e6552e57ecf..1434c502e340 100644
--- a/drivers/base/regmap/regmap-spi.c
+++ b/drivers/base/regmap/regmap-spi.c
@@ -123,6 +123,10 @@ static const struct regmap_bus *regmap_get_spi_bus(struct spi_device *spi,
 		bus->free_on_exit = true;
 		bus->max_raw_read = max_size;
 		bus->max_raw_write = max_size;
+
+		if (spi_max_message_size(spi) != SIZE_MAX)
+			bus->max_combined_rw = spi_max_message_size(spi);
+
 		return bus;
 	}
 
diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 21a0c2562ec0..a99152f010f8 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -735,6 +735,7 @@ struct regmap *__regmap_init(struct device *dev,
 	struct regmap *map;
 	int ret = -EINVAL;
 	enum regmap_endian reg_endian, val_endian;
+	size_t reg_pad_size;
 	int i, j;
 
 	if (!config)
@@ -840,6 +841,20 @@ struct regmap *__regmap_init(struct device *dev,
 	if (bus) {
 		map->max_raw_read = bus->max_raw_read;
 		map->max_raw_write = bus->max_raw_write;
+		if (bus->max_combined_rw) {
+			reg_pad_size = map->format.reg_bytes + map->format.pad_bytes;
+
+			if (map->max_raw_read + reg_pad_size > bus->max_combined_rw)
+				map->max_raw_read -= reg_pad_size;
+			if (map->max_raw_write + reg_pad_size > bus->max_combined_rw)
+				map->max_raw_write -= reg_pad_size;
+
+			if (map->max_raw_read  < map->format.buf_size ||
+			    map->max_raw_write < map->format.buf_size) {
+				ret = -EINVAL;
+				goto err_hwlock;
+			}
+		}
 	}
 	map->dev = dev;
 	map->bus = bus;
diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index e3c9a25a853a..a720f578b8e6 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -506,6 +506,8 @@ typedef void (*regmap_hw_free_context)(void *context);
  * @max_raw_read: Max raw read size that can be used on the bus.
  * @max_raw_write: Max raw write size that can be used on the bus.
  * @free_on_exit: kfree this on exit of regmap
+ * @max_combined_rw: Max size for raw_read + raw_write, when they are issued
+ *                   together as part of the same message
  */
 struct regmap_bus {
 	bool fast_io;
@@ -523,6 +525,7 @@ struct regmap_bus {
 	enum regmap_endian val_format_endian_default;
 	size_t max_raw_read;
 	size_t max_raw_write;
+	size_t max_combined_rw;
 	bool free_on_exit;
 };
 
-- 
2.33.0