[PATCH 3/9] regmap: spi: SPI_CONTROLLER_CS_PER_TRANSFER affects max read/write

[Lucas Tanure <tanureal@xxxxxxxxxxxxxxxxxxxxx>]

regmap-spi will split data and address between two transfers in the
same message so use addr_affects_max_raw_rw to flag that the number
bytes to read or write should be a little less (address + padding size),
so that the SPI controller can merge the entire message into a single
CS period

Signed-off-by: Lucas Tanure <tanureal@xxxxxxxxxxxxxxxxxxxxx>
---
 drivers/base/regmap/regmap-spi.c | 14 ++++++++++++--
 drivers/base/regmap/regmap.c     |  9 +++++++++
 include/linux/regmap.h           |  2 ++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/base/regmap/regmap-spi.c b/drivers/base/regmap/regmap-spi.c
index 603a4c1c2066..0c1f2e51c0c7 100644
--- a/drivers/base/regmap/regmap-spi.c
+++ b/drivers/base/regmap/regmap-spi.c
@@ -115,12 +115,22 @@ static const struct regmap_bus *regmap_get_spi_bus(struct spi_device *spi,
 	struct spi_master *master = spi->master;
 	struct regmap_bus *bus = NULL;
 
-	if (master->max_transfer_size) {
+	if (master->max_transfer_size || (master->flags & SPI_CONTROLLER_CS_PER_TRANSFER)) {
 		bus = kmemdup(&regmap_spi, sizeof(*bus), GFP_KERNEL);
 		if (!bus)
 			return ERR_PTR(-ENOMEM);
 		bus->free_on_exit = true;
-		bus->max_raw_read = bus->max_raw_write = master->max_transfer_size(spi);
+
+		/* regmap-spi will split data and address between two transfers in the same message
+		 * so use addr_affects_max_raw_rw to flag that the number bytes to read or write
+		 * should be a little less (address + padding size), so the controller can
+		 * fit both transfers in a single CS period
+		 */
+		bus->addr_affects_max_raw_rw = master->flags & SPI_CONTROLLER_CS_PER_TRANSFER;
+
+		if (master->max_transfer_size)
+			bus->max_raw_read = bus->max_raw_write = master->max_transfer_size(spi);
+
 		return bus;
 	}
 
diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 6ad41d0720ba..31d0949b6c2f 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -815,6 +815,15 @@ 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->addr_affects_max_raw_rw) {
+			if (map->max_raw_read  < map->format.buf_size ||
+			    map->max_raw_write < map->format.buf_size) {
+				ret = -EINVAL;
+				goto err_name;
+			}
+			map->max_raw_read -= (map->format.reg_bytes + map->format.pad_bytes);
+			map->max_raw_write -= (map->format.reg_bytes + map->format.pad_bytes);
+		}
 	}
 	map->dev = dev;
 	map->bus = bus;
diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index 77755196277c..a90d1e270b1f 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -504,6 +504,7 @@ 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
+ * @addr_affects_max_raw_rw: max_raw_[read|write] must include the address and padding preamble
  */
 struct regmap_bus {
 	bool fast_io;
@@ -522,6 +523,7 @@ struct regmap_bus {
 	size_t max_raw_read;
 	size_t max_raw_write;
 	bool free_on_exit;
+	bool addr_affects_max_raw_rw;
 };
 
 /*
-- 
2.33.0