Re: [PATCH v2 1/4] spi: allow ancillary devices to share parent's chip selects

On 2/6/26 10:07 AM, Antoniu Miclaus wrote:

When registering an ancillary SPI device, the current code flags a chip
select conflict with the parent device. This happens because the
ancillary device intentionally uses one of the parent's chip selects,
but __spi_add_device() checks against all existing devices including
the parent.

Allow this by passing the parent device pointer to __spi_add_device()
and skipping the conflict check when the existing device is the parent.

...

 static int spi_dev_check(struct device *dev, void *data)
 {
 	struct spi_device *spi = to_spi_device(dev);
-	struct spi_device *new_spi = data;
+	struct spi_dev_check_info *info = data;
+	struct spi_device *new_spi = info->new_spi;
 	int status, idx;
 
+	/*
+	 * When registering an ancillary device, skip checking against the
+	 * parent device since the ancillary is intentionally using one of
+	 * the parent's chip selects.
+	 */
+	if (info->parent && spi == info->parent)

spi should never be NULL (or we would get a segfault later), so
if `(spi == info->parent)` should be enough.

+		return 0;
+

Reviewed-by: David Lechner <dlechner@baylibre.com>