Hi, On Wed, 28 Sept 2022 at 01:24, AKASHI Takahiro <takahiro.aka...@linaro.org> wrote: > > On Wed, Sep 28, 2022 at 08:57:43AM +0200, Heinrich Schuchardt wrote: > > > > > > On 9/28/22 03:54, Simon Glass wrote: > > > Hi, > > > > > > On Tue, 27 Sept 2022 at 00:53, Heinrich Schuchardt > > > <heinrich.schucha...@canonical.com> wrote: > > > > > > > > > > > > > > > > On 9/27/22 03:51, AKASHI Takahiro wrote: > > > > > On Mon, Sep 26, 2022 at 08:06:52AM +0200, Heinrich Schuchardt wrote: > > > > > > > > > > > > > > > > > > On 9/16/22 02:58, AKASHI Takahiro wrote: > > > > > > > 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.) > > > > > > > > > > > > This behavior matches what EDK II does if you remove a device and > > > > > > create a > > > > > > new device. > > > > > > > > > > I don't think that EDK2 has "scsi rescan" or others, which users can > > > > > invoke > > > > > at any time. Moreover, I believe that EDK2 code (drivers) checks > > > > > whether a device > > > > > is really changed or not before updating a MediaId. > > > > > > > > > > > If a device is removed and recreated anything could have happened > > > > > > in between > > > > > > like complete repartitioning. We cannot assume that any cached > > > > > > state is > > > > > > valid anymore even if GUIDs are the same. > > > > > > > > > > I'm not sure if you fully understand my point. > > > > > My assumption is the case where a device is NOT removed around "scsi > > > > > rescan" > > > > > (or usb stop/start) and stays online. In this case, > > > > > 1. access to, say, "scsi 0:1", via UEFI BLOCK_IO succeeds > > > > > 2. "scsi rescan" > > > > > 3. access to the same device, "scsi 0:1", via UEFI BLOCK_IO > > > > > currently (3) succeeds, but with your patch, it may potentially fail > > > > > because > > > > > of media_id altered. > > > > > > > > > > I admit that it will not happen under the current UEFI implementation > > > > > because > > > > > non of UEFI applications will survive across command lines and none > > > > > of information, > > > > > including media_id or handle, can be carried over from (1) to (3). > > > > > But unconditionally incrementing an internally-held media_id, as in > > > > > your patch, > > > > > is a wrong behavior. > > > > > > > > The patch issues a new media ID if a new device is probed which only > > > > happens to have the same device number if another device of that number > > > > was removed before. > > > > > > > > Commands like 'usb scan' don't necessarily issue the same numbers to the > > > > same device as before the command if a new device has been attached in > > > > the meanwhile. > > > > > > > > Assuming that a new device contains the same medium as an old one > > > > because by chance it has the same device number is definitively unsafe. > > > > > > > > If a device is probed, we have to assume that it contains a new medium. > > > > > > Sorry if I repeat myself, but this sort of thing should be handled in > > > the driver model code. Can we get some more progress on integrating > > > the EFI layer better? > > > > The last mails where about *whether* the media ID should be bumped after a > > block device has been created and not about where we will implement it. > > Indeed. I don't care "where" for now, but "how" or "whether". > > The most essential issue is that none of U-Boot block device drivers has > ability of detecting media insertion or removal immediately > (due to the lack of interrupt support). > This is even not related to DM or not.
This could be implemented using the cyclic feature now present, or perhaps using an IDLE event I am planning to introduce for VBE. But another way is to have a command to indicate that the device has been removed. Regards, Simon