spi: keep track of number of chipselects in spi_device

There are several places where we need to iterate over a device's
chipselect. To be able to do it efficiently, store the number of
chipselects in spi_device, like we do for controllers.

Since we now use a device supplied value, add a check to make sure it
isn't more than we can support.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Link: https://patch.msgid.link/20250915183725.219473-3-jonas.gorski@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: KanjiMonster

drivers/spi/spi.c

@@ -586,6 +586,7 @@ struct spi_device *spi_alloc_device(struct spi_controller *ctlr)
 	spi->dev.bus = &spi_bus_type;
 	spi->dev.release = spidev_release;
 	spi->mode = ctlr->buswidth_override_bits;
+	spi->num_chipselect = 1;
 
 	device_initialize(&spi->dev);
 	return spi;
@@ -635,7 +636,7 @@ static inline int spi_dev_check_cs(struct device *dev,
 	u8 idx_new;
 
 	cs = spi_get_chipselect(spi, idx);
-	for (idx_new = new_idx; idx_new < SPI_CS_CNT_MAX; idx_new++) {
+	for (idx_new = new_idx; idx_new < new_spi->num_chipselect; idx_new++) {
 		cs_new = spi_get_chipselect(new_spi, idx_new);
 		if (is_valid_cs(cs) && is_valid_cs(cs_new) && cs == cs_new) {
 			dev_err(dev, "chipselect %u already in use\n", cs_new);
@@ -652,7 +653,7 @@ static int spi_dev_check(struct device *dev, void *data)
 	int status, idx;
 
 	if (spi->controller == new_spi->controller) {
-		for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
+		for (idx = 0; idx < spi->num_chipselect; idx++) {
 			status = spi_dev_check_cs(dev, spi, idx, new_spi, 0);
 			if (status)
 				return status;
@@ -674,7 +675,13 @@ static int __spi_add_device(struct spi_device *spi)
 	int status, idx;
 	u8 cs;
 
-	for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
+	if (spi->num_chipselect > SPI_CS_CNT_MAX) {
+		dev_err(dev, "num_cs %d > max %d\n", spi->num_chipselect,
+			SPI_CS_CNT_MAX);
+		return -EOVERFLOW;
+	}
+
+	for (idx = 0; idx < spi->num_chipselect; idx++) {
 		/* Chipselects are numbered 0..max; validate. */
 		cs = spi_get_chipselect(spi, idx);
 		if (is_valid_cs(cs) && cs >= ctlr->num_chipselect) {
@@ -689,7 +696,7 @@ static int __spi_add_device(struct spi_device *spi)
 	 * For example, spi->chip_select[0] != spi->chip_select[1] and so on.
 	 */
 	if (!spi_controller_is_target(ctlr)) {
-		for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
+		for (idx = 0; idx < spi->num_chipselect; idx++) {
 			status = spi_dev_check_cs(dev, spi, idx, spi, idx + 1);
 			if (status)
 				return status;
@@ -717,7 +724,7 @@ static int __spi_add_device(struct spi_device *spi)
 	if (ctlr->cs_gpiods) {
 		u8 cs;
 
-		for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
+		for (idx = 0; idx < spi->num_chipselect; idx++) {
 			cs = spi_get_chipselect(spi, idx);
 			if (is_valid_cs(cs))
 				spi_set_csgpiod(spi, idx, ctlr->cs_gpiods[cs]);
@@ -1024,7 +1031,7 @@ static void spi_res_release(struct spi_controller *ctlr, struct spi_message *mes
 
 /*-------------------------------------------------------------------------*/
 #define spi_for_each_valid_cs(spi, idx)				\
-	for (idx = 0; idx < SPI_CS_CNT_MAX; idx++)		\
+	for (idx = 0; idx < spi->num_chipselect; idx++)		\
 		if (!(spi->cs_index_mask & BIT(idx))) {} else
 
 static inline bool spi_is_last_cs(struct spi_device *spi)
@@ -1080,8 +1087,12 @@ static void spi_set_cs(struct spi_device *spi, bool enable, bool force)
 	trace_spi_set_cs(spi, activate);
 
 	spi->controller->last_cs_index_mask = spi->cs_index_mask;
-	for (idx = 0; idx < SPI_CS_CNT_MAX; idx++)
-		spi->controller->last_cs[idx] = enable ? spi_get_chipselect(spi, 0) : SPI_INVALID_CS;
+	for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
+		if (enable && idx < spi->num_chipselect)
+			spi->controller->last_cs[idx] = spi_get_chipselect(spi, 0);
+		else
+			spi->controller->last_cs[idx] = SPI_INVALID_CS;
+	}
 
 	spi->controller->last_cs_mode_high = spi->mode & SPI_CS_HIGH;
 	if (spi->controller->last_cs_mode_high)
@@ -2452,6 +2463,8 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 		dev_err(&ctlr->dev, "SPI controller doesn't support multi CS\n");
 		return -EINVAL;
 	}
+
+	spi->num_chipselect = rc;
 	for (idx = 0; idx < rc; idx++)
 		spi_set_chipselect(spi, idx, cs[idx]);
 

include/linux/spi/spi.h

@@ -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)
@@ -229,6 +230,7 @@ struct spi_device {
 	struct spi_delay	cs_inactive;
 
 	u8			chip_select[SPI_CS_CNT_MAX];
+	u8			num_chipselect;
 
 	/*
 	 * Bit mask of the chipselect(s) that the driver need to use from
@@ -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;
 	}