On Thu, Sep 15, 2022 at 10:02:40PM +0200, Heinrich Schuchardt wrote:
The medium a device like 'mmc 0' or 'usb 0' points to may change over time. Hence device type and number are not sufficient to identify the inserted medium. The same is true for the device path generated for such a device.
Well, it depends on how a device path is generated in U-Boot's UEFI implementation. I believe that a device path represents an "unique path" to a given device however this device is enumerated. In this sense, the current dp_fill()/efi_dp_from_part() is not a right implementation as it relies on device numbers. Furthermore, a generated device path here is different from one generated by EDK2 (even if both software are run on the same board).
This is an issue that I used to tackle in https://lists.denx.de/pipermail/u-boot/2021-November/468216.html although I have since had no progress.
This is why the EFI_BLOCK_IO_PROTOCOL provides a field MediaId.
Whenever a removable medium is changed or a new block device with a previously used device path is created we should provide a different MediaID.
This series adds a field media_id to the block device descriptor and fills it after probing. The value of the field is then copied to the EFI_BLOCK_IO_PROTOCOL.
I'm afraid that your patch doesn't always work as you expect. When "scsi rescan" or "usb stop; usb start", for instance, is invoked, all the existing devices and associated blk_desc structures are once freed and even if nothing is changed, i.e. a device is neither removed nor added, the exact same structures will be re-created. With your patch applied, however, a new (and different) "media_id" will be assigned to an existing device. UEFI User may be notified of "media change". (To be honest, this is quite unlikely because the current UEFI implementation doesn't use BLOCK_IO_PROTOCOL internally, say, for file system access.)
-Takahiro Akashi
With future patches we can refine this in sub-systems like USB, MMC, SCSI to indicate media changes
Heinrich Schuchardt (2): dm: blk: assign media ID to block devices efi_loader: fill media_id from block device descriptor
drivers/block/blk-uclass.c | 16 +++++++++++++++- include/blk.h | 11 +++++++++++ lib/efi_loader/efi_disk.c | 6 +----- 3 files changed, 27 insertions(+), 6 deletions(-)
-- 2.37.2