[PATCH v4 4/9] spi: restrict CS logical values to a contiguous sequence

[Jonathan Santos <Jonathan.Santos@analog.com>]

When a device uses more than one chip select, require the logical CS
numbers to be consecutive (for example 2, 3, 4). If they aren't,
__spi_add_device() now fails with -EINVAL and logs which CS breaks
the sequence.

Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
---
Changes in v4:
* New patch, suggested by Andy. I assume this might have impacts on
  existing users. Should we make something else to complement this?
---
 drivers/spi/spi.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 7a0406ec200e..2b2eeaa4c15d 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -902,6 +902,16 @@ static int __spi_add_device(struct spi_device *spi, struct spi_device *parent)
 	for (idx = spi->num_chipselect; idx < SPI_DEVICE_CS_CNT_MAX; idx++)
 		spi_set_chipselect(spi, idx, SPI_INVALID_CS);
 
+	/* Restrict CS logical values to a contiguous sequence */
+	for (idx = 1; idx < spi->num_chipselect; idx++) {
+		if (spi_get_chipselect(spi, idx) != spi_get_chipselect(spi, idx - 1) + 1) {
+			dev_err(dev, "cs%d is not consecutive with cs%d\n",
+				spi_get_chipselect(spi, idx),
+				spi_get_chipselect(spi, idx - 1));
+			return -EINVAL;
+		}
+	}
+
 	/* Set the bus ID string */
 	spi_dev_set_name(spi);
 
-- 
2.34.1