[BUG] issues with new bootflow, uefi and virtio

[Vincent Stehlé]

Hi,

I am hitting an issue with the new bootflow when booting with UEFI from a
virtio device on Qemu Arm.

It seems the device number computation in efiload_read_file() does not work
in the general virtio case, where it will pick the virtio device number
instead of the block device index. On Qemu arm virt machine, many virtio
mmio devices are provisioned in the memory map and no assumption can be
made on the number of the actual virtio device in use in the general case.

This is an extract of the output of `dm tree' on this platform, focused on
the virtio device from which I would like to boot:

  virtio    31  [ + ]   virtio-mmio     |-- virtio_mmio at a003e00
  blk        0  [ + ]   virtio-blk      |   |-- virtio-blk#31
  partition  0  [ + ]   blk_partition   |   |   |-- virtio-blk#31:1
  partition  1  [ + ]   blk_partition   |   |   `-- virtio-blk#31:2
  bootdev    2  [ + ]   virtio_bootdev  |   `-- virtio-blk#31.bootdev

In this extract the actual virtio device number is 31, as will be picked by
efiload_read_file(), but the desired block device index is zero, as would
be used with e.g. `ls virtio 0'.

This can be reproduced for example with Buildroot
qemu_aarch64_ebbr_defconfig or qemu_arm_ebbr_defconfig and updating the
U-Boot version to v2023.04. This was working properly with U-Boot versions
up to v2023.01.

This seems to be very specific to virtio, as the numbers align much more
nicely for e.g. USB mass storage or NVMe.

To help debugging, the following patch forces the device number to zero in
the case of virtio, which allows to boot again with UEFI and virtio on Qemu
Arm. Hopefully this should give a hint of what is going on.

I tried to create a fix by looking for the first child device of
UCLASS_BLK, and use its devnum instead in the case of virtio. Sadly, I am
not able to confirm if this is a proper fix as I am hitting other boot
issues in the case of multiple boot devices of the same class it seems...

Vincent.

[1]: https://buildroot.org

---
 boot/bootmeth_efi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/boot/bootmeth_efi.c b/boot/bootmeth_efi.c
index 6a97ac02ff5..e5b0d8614ff 100644
--- a/boot/bootmeth_efi.c
+++ b/boot/bootmeth_efi.c
@@ -117,7 +117,9 @@ static int efiload_read_file(struct blk_desc *desc, struct bootflow *bflow)
 	 * this can go away.
 	 */
 	media_dev = dev_get_parent(bflow->dev);
-	snprintf(devnum_str, sizeof(devnum_str), "%x", dev_seq(media_dev));
+	snprintf(devnum_str, sizeof(devnum_str), "%x",
+		 device_get_uclass_id(media_dev) == UCLASS_VIRTIO ? 0 :
+		 dev_seq(media_dev));
 
 	strlcpy(dirname, bflow->fname, sizeof(dirname));
 	last_slash = strrchr(dirname, '/');
-- 
2.39.2