spi: multi CS cleanup and controller CS limit

Merge series from Jonas Gorski <jonas.gorski@gmail.com>:

This series aims at cleaning up the current multi CS parts and removing
the CS limit per controller that was introduced with the multi CS
support.

To do this, store the assigned chip selects per device in
spi_device::num_chipselects, which allows us to use that instead of
SPI_CS_CNT_MAX for most loops, as well as remove the check for
SPI_INVALID_CS for any chip select.

This should hopefully make it obvious that SPI_CS_CNT_MAX only limits
accesses to arrays indexed by the number of chip selects of a device,
not the controller, and we can remove the check for
spi_controller::num_chipselects being less than SPI_CS_CNT_MAX in device
registration (which was the wrong place to do that anyway).

After having done that, we can reduce SPI_CS_CNT_MAX again to 4 without
breaking devices on higher CS lines.

Finally, rename SPI_CS_CNT_MAX to SPI_DEVICE_CNT_MAX to make it more
clear that this limit only applies to devices, not controllers.

There are still more issues left, but these can be addressed in future
submissions:

* The code allows multi-cs devices for any controller, as long as the
  device does not set parallel-memories.
* No current spi controller driver handles logical chip selects other
  than the first one, and always use it, regardless what cs_index_mask
  says.
* While most spi controllers should be able to handle devices that have
  multiple cs that just get enabled selectively, but not at the same
  time, there is no way to tell that to the core (ties into the above).
* There is no parallel memories/multi cs flag for devices, so any
  implementing driver needs to check the device tree node, making it
  impossible to register these kind of devices via platform code.

1 files changed, 9 insertions, 7 deletions

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index e9ea43234d9a..cb2c2df31089 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -21,7 +21,7 @@
 #include <uapi/linux/spi/spi.h>
 
 /* Max no. of CS supported per spi device */
-#define SPI_CS_CNT_MAX 24
+#define SPI_DEVICE_CS_CNT_MAX 4
 
 struct dma_chan;
 struct software_node;
@@ -170,6 +170,7 @@ extern void spi_transfer_cs_change_delay_exec(struct spi_message *msg,
  *	two delays will be added up.
  * @chip_select: Array of physical chipselect, spi->chipselect[i] gives
  *	the corresponding physical CS for logical CS i.
+ * @num_chipselect: Number of physical chipselects used.
  * @cs_index_mask: Bit mask of the active chipselect(s) in the chipselect array
  * @cs_gpiod: Array of GPIO descriptors of the corresponding chipselect lines
  *	(optional, NULL when not using a GPIO line)
@@ -228,7 +229,8 @@ struct spi_device {
 	struct spi_delay	cs_hold;
 	struct spi_delay	cs_inactive;
 
-	u8			chip_select[SPI_CS_CNT_MAX];
+	u8			chip_select[SPI_DEVICE_CS_CNT_MAX];
+	u8			num_chipselect;
 
 	/*
 	 * Bit mask of the chipselect(s) that the driver need to use from
@@ -236,9 +238,9 @@ struct spi_device {
 	 * multiple chip selects & memories are connected in parallel
 	 * then more than one bit need to be set in cs_index_mask.
 	 */
-	u32			cs_index_mask : SPI_CS_CNT_MAX;
+	u32			cs_index_mask : SPI_DEVICE_CS_CNT_MAX;
 
-	struct gpio_desc	*cs_gpiod[SPI_CS_CNT_MAX];	/* Chip select gpio desc */
+	struct gpio_desc	*cs_gpiod[SPI_DEVICE_CS_CNT_MAX];	/* Chip select gpio desc */
 
 	/*
 	 * Likely need more hooks for more protocol options affecting how
@@ -315,7 +317,7 @@ static inline bool spi_is_csgpiod(struct spi_device *spi)
 {
 	u8 idx;
 
-	for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
+	for (idx = 0; idx < spi->num_chipselect; idx++) {
 		if (spi_get_csgpiod(spi, idx))
 			return true;
 	}
@@ -719,8 +721,8 @@ struct spi_controller {
 	bool				auto_runtime_pm;
 	bool                            fallback;
 	bool				last_cs_mode_high;
-	s8				last_cs[SPI_CS_CNT_MAX];
-	u32				last_cs_index_mask : SPI_CS_CNT_MAX;
+	s8				last_cs[SPI_DEVICE_CS_CNT_MAX];
+	u32				last_cs_index_mask : SPI_DEVICE_CS_CNT_MAX;
 	struct completion               xfer_completion;
 	size_t				max_dma_len;