[PATCH 1/2] efi_loader: firmware: decouple dfu_alt_num from image_index

RAW capsule updates assume dfu_alt_num is always image_index - 1, i.e.
that fw_images[] is a positionally-ordered mirror of the DFU alt
settings. That holds for every board that builds its fw_images[] table
by hand, but a platform whose image list is discovered at runtime
(varying per board, with gaps for missing components) can't guarantee
image_index and dfu_alt_num stay in lockstep.

Move the (image_index - 1) calculation into a __weak function that
platforms can override, following the pattern already used for
efi_firmware_get_image_type_id(). The default keeps the
existing behaviour, so no other board needs any change.

Signed-off-by: Balaji Selvanathan <[email protected]>
---
 include/efi_loader.h          | 17 +++++++++++++++++
 lib/efi_loader/efi_firmware.c | 21 +++++++++++++++++++--
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/include/efi_loader.h b/include/efi_loader.h
index 3a4d502631c..6626674f738 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -1187,11 +1187,15 @@ efi_status_t efi_capsule_authenticate(const void *capsule,
  * @fw_name:		Name of the firmware image
  * @image_index:	Image Index, same as value passed to SetImage FMP
  *                      function
+ * @dfu_alt_num:	DFU alt setting number for this image. Only consulted
+ *                      by a platform's efi_firmware_get_dfu_alt_num()
+ *                      override
  */
 struct efi_fw_image {
 	efi_guid_t image_type_id;
 	u16 *fw_name;
 	u8 image_index;
+	u8 dfu_alt_num;
 };
 
 /**
@@ -1240,6 +1244,19 @@ efi_status_t efi_ecpt_register(void);
 efi_status_t efi_esrt_populate(void);
 efi_status_t efi_load_capsule_drivers(void);
 
+/**
+ * efi_firmware_get_dfu_alt_num() - get the DFU alt setting number for an image
+ * @image_index:	image index
+ *
+ * Return the DFU alt setting number to use when writing the image
+ * identified by @image_index. Weak default derives it positionally as
+ * (image_index - 1); a platform whose fw_images[] is not laid out 1:1 with
+ * DFU alt numbers should override this function.
+ *
+ * Return:		DFU alt setting number
+ */
+u8 efi_firmware_get_dfu_alt_num(u8 image_index);
+
 efi_status_t platform_get_eventlog(struct udevice *dev, u64 *addr, u32 *sz);
 
 efi_status_t efi_locate_handle_buffer_int(enum efi_locate_search_type search_type,
diff --git a/lib/efi_loader/efi_firmware.c b/lib/efi_loader/efi_firmware.c
index b41969c70fd..c7339412055 100644
--- a/lib/efi_loader/efi_firmware.c
+++ b/lib/efi_loader/efi_firmware.c
@@ -80,6 +80,22 @@ efi_guid_t *efi_firmware_get_image_type_id(u8 image_index)
 	return NULL;
 }
 
+/**
+ * efi_firmware_get_dfu_alt_num - get the DFU alt setting number for an image
+ * @image_index:	image index
+ *
+ * Return the DFU alt setting number to use when writing the image
+ * identified by @image_index. The generic default derives it positionally
+ * from @image_index; a platform whose fw_images[] is not laid out 1:1 with
+ * DFU alt numbers should override this function.
+ *
+ * Return:		DFU alt setting number
+ */
+u8 __weak efi_firmware_get_dfu_alt_num(u8 image_index)
+{
+	return image_index - 1;
+}
+
 /* Place holder; not supported */
 static
 efi_status_t EFIAPI efi_firmware_get_image_unsupported(
@@ -768,9 +784,10 @@ efi_status_t EFIAPI efi_firmware_raw_set_image(
 	/*
 	 * dfu_alt_num is assigned from 0 while image_index starts from 1.
 	 * dfu_alt_num is calculated by (image_index - 1) when multi bank update
-	 * is not used.
+	 * is not used. A platform may override efi_firmware_get_dfu_alt_num()
+	 * if its fw_images[] is not laid out 1:1 with DFU alt numbers.
 	 */
-	dfu_alt_num = image_index - 1;
+	dfu_alt_num = efi_firmware_get_dfu_alt_num(image_index);
 	if (IS_ENABLED(CONFIG_FWU_MULTI_BANK_UPDATE)) {
 		/*
 		 * Based on the value of update bank, derive the

-- 
2.34.1