2 files changed, 23 insertions, 1 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 47eff8012a77..2c0c26a57f03 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1581,13 +1581,30 @@ static void of_register_spi_devices(struct spi_master *master) { }
 static int acpi_spi_add_resource(struct acpi_resource *ares, void *data)
 {
         struct spi_device *spi = data;
+        struct spi_master *master = spi->master;
 
         if (ares->type == ACPI_RESOURCE_TYPE_SERIAL_BUS) {
                 struct acpi_resource_spi_serialbus *sb;
 
                 sb = &ares->data.spi_serial_bus;
                 if (sb->type == ACPI_RESOURCE_SERIAL_TYPE_SPI) {
-                        spi->chip_select = sb->device_selection;
+                        /*
+                         * ACPI DeviceSelection numbering is handled by the
+                         * host controller driver in Windows and can vary
+                         * from driver to driver. In Linux we always expect
+                         * 0 .. max - 1 so we need to ask the driver to
+                         * translate between the two schemes.
+                         */
+                        if (master->fw_translate_cs) {
+                                int cs = master->fw_translate_cs(master,
+                                                sb->device_selection);
+                                if (cs < 0)
+                                        return cs;
+                                spi->chip_select = cs;
+                        } else {
+                                spi->chip_select = sb->device_selection;
+                        }
+
                         spi->max_speed_hz = sb->connection_speed;
 
                         if (sb->clock_phase == ACPI_SPI_SECOND_PHASE)
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 53be3a4c60cb..8a25e6c2fb56 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -369,6 +369,9 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  * @dma_rx: DMA receive channel
  * @dummy_rx: dummy receive buffer for full-duplex devices
  * @dummy_tx: dummy transmit buffer for full-duplex devices
+ * @fw_translate_cs: If the boot firmware uses different numbering scheme
+ *      what Linux expects, this optional hook can be used to translate
+ *      between the two.
  *
  * Each SPI master controller can communicate with one or more @spi_device
  * children.  These make a small bus, sharing MOSI, MISO and SCK signals
@@ -537,6 +540,8 @@ struct spi_master {
         /* dummy data for full duplex devices */
         void                    *dummy_rx;
         void                    *dummy_tx;
+
+        int (*fw_translate_cs)(struct spi_master *master, unsigned cs);
 };
 
 static inline void *spi_master_get_devdata(struct spi_master *master)