[U-Boot] [PATCH v2 2/3] efi_loader: enumerate disk devices every time

Alexander Graf
2019-01-11T07:57:05Z

On 11.01.19 05:29, AKASHI Takahiro wrote:
> Alex, Heinrich and Simon,
>
> Thank you for your comments, they are all valuable but also make me
> confused as different people have different requirements :)
> I'm not sure that all of us share the same *ultimate* goal here.

The shared ultimate goal is to "merge" (as Simon put it) dm and efi objects.

But we have this annoying interim state where we would lose a few boards
because they haven't been converted to DM. That's what keeps us from it.

I think what this discussion boils down to is that someone needs to
start prototyping the DM/EFI integration. Start off with a simple
subsystem, like BLK. Then provide a DM path and have a non-DM fallback
still in its own source file that also provides EFI BLK devices.
Eventually we just remove the latter.

That way we can then work on getting hotplug working in the DM path,
which is the one we want anyway. For non-DM, you simply miss out on that
amazing new feature, but we don't regress users.

> So, first, let me reply to each of your comments.
> Through this process, I hope we will have better understandings
> of long-term solution as well as a tentative fix.
>
> On Thu, Jan 10, 2019 at 10:22:04AM +0100, Alexander Graf wrote:
>>
>>
>>> Am 10.01.2019 um 10:16 schrieb AKASHI Takahiro <takahiro.akashi@linaro.org>:
>>>
>>>> On Thu, Jan 10, 2019 at 09:15:36AM +0100, Alexander Graf wrote:
>>>>
>>>>
>>>>>> Am 10.01.2019 um 09:02 schrieb AKASHI Takahiro <takahiro.akashi@linaro.org>:
>>>>>>
>>>>>> On Thu, Jan 10, 2019 at 08:30:13AM +0100, Alexander Graf wrote:
>>>>>>
>>>>>>
>>>>>>> On 10.01.19 08:26, AKASHI Takahiro wrote:
>>>>>>> Alex,
>>>>>>>
>>>>>>>> On Thu, Jan 10, 2019 at 07:21:12AM +0100, Alexander Graf wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>> On 10.01.19 03:13, AKASHI Takahiro wrote:
>>>>>>>>> Alex,
>>>>>>>>>
>>>>>>>>>> On Wed, Jan 09, 2019 at 10:06:16AM +0100, Alexander Graf wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> On 13.12.18 08:58, AKASHI Takahiro wrote:
>>>>>>>>>>> Heinrich,
>>>>>>>>>>>
>>>>>>>>>>>>> On Tue, Dec 11, 2018 at 08:55:41PM +0100, Heinrich Schuchardt wrote:
>>>>>>>>>>>>> On 11/15/18 5:58 AM, AKASHI Takahiro wrote:
>>>>>>>>>>>>> Currently, efi_init_obj_list() scan disk devices only once, and never
>>>>>>>>>>>>> change a list of efi disk devices. This will possibly result in failing
>>>>>>>>>>>>> to find a removable storage which may be added later on. See [1].
>>>>>>>>>>>>>
>>>>>>>>>>>>> In this patch, called is efi_disk_update() which is responsible for
>>>>>>>>>>>>> re-scanning UCLASS_BLK devices and removing/adding efi disks if necessary.
>>>>>>>>>>>>>
>>>>>>>>>>>>> For example,
>>>>>>>>>>>>>
>>>>>>>>>>>>> => efishell devices
>>>>>>>>>>>>> Scanning disk pci_mmc.blk...
>>>>>>>>>>>>> Found 3 disks
>>>>>>>>>>>>> Device Name
>>>>>>>>>>>>> ============================================
>>>>>>>>>>>>> /VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b)
>>>>>>>>>>>>> /VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b)/SD(0)/SD(0)
>>>>>>>>>>>>> /VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b)/SD(0)/SD(0)/HD(2,MBR,0x086246ba,0x40800,0x3f800)
>>>>>>>>>>>>> => usb start
>>>>>>>>>>>>> starting USB...
>>>>>>>>>>>>> USB0: USB EHCI 1.00
>>>>>>>>>>>>> scanning bus 0 for devices... 3 USB Device(s) found
>>>>>>>>>>>>> scanning usb for storage devices... 1 Storage Device(s) found
>>>>>>>>>>>>> => efishell devices
>>>>>>>>>>>>> Scanning disk usb_mass_storage.lun0...
>>>>>>>>>>>>> Device Name
>>>>>>>>>>>>> ============================================
>>>>>>>>>>>>> /VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b)
>>>>>>>>>>>>> /VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b)/SD(0)/SD(0)
>>>>>>>>>>>>> /VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b)/SD(0)/SD(0)/HD(2,MBR,0x086246ba,0x40800,0x3f800)
>>>>>>>>>>>>> /VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b)/USBClass(0,0,9,0,1)/USBClass(46f4,1,0,0,0)/HD(1,0x01,0,0x40,0x14fe4c)
>>>>>>>>>>>>>
>>>>>>>>>>>>> Without this patch, the last device, USB mass storage, won't show up.
>>>>>>>>>>>>>
>>>>>>>>>>>>> [1] https://lists.denx.de/pipermail/u-boot/2018-October/345307.html
>>>>>>>>>>>>>
>>>>>>>>>>>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>>>>>>>>>>>>
>>>>>>>>>>>> Why should we try to fix something in the EFI subsystems that goes wrong
>>>>>>>>>>>> in the handling of device enumeration.
>>>>>>>>>>>
>>>>>>>>>>> No.
>>>>>>>>>>> This is a natural result from how efi disks are currently implemented on u-boot.
>>>>>>>>>>> Do you want to totally re-write/re-implement efi disks?
>>>>>>>>>>
>>>>>>>>>> Could we just make this event based for now? Call a hook from the
>>>>>>>>>> storage dm subsystem when a new u-boot block device gets created to
>>>>>>>>>> issue a sync of that in the efi subsystem?
>>>>>>>>>
>>>>>>>>> If I correctly understand you, your suggestion here corresponds
>>>>>>>>> with my proposal#3 in [1] while my current approach is #2.
>>>>>>>>>
>>>>>>>>> [1] https://lists.denx.de/pipermail/u-boot/2018-October/345307.html
>>>>>>>>
>>>>>>>> Yes, I think so.
>>>>>>>>
>>>>>>>>> So we will call, say, efi_disk_create(struct udevice *) in
>>>>>>>>> blk_create_device() and efi_dsik_delete() in blk_unbind_all().
>>>>>>>>
>>>>>>>> I would prefer if we didn't call them directly, but through an event
>>>>>>>> mechanism. So the efi_disk subsystem registers an event with the dm
>>>>>>>> block subsystem and that will just call all events when block devices
>>>>>>>> get created which will automatically also include the efi disk creation
>>>>>>>> callback. Same for reverse.
>>>>>>>
>>>>>>> Do you mean efi event by "event?"
>>>>>>> (I don't think there is any generic event interface on DM side.)
>>>>>>>
>>>>>>> Whatever an "event" is or whether we call efi_disk_create() directly
>>>>>>> or indirectly via an event, there is one (big?) issue in this approach
>>>>>>> (while I've almost finished prototyping):
>>>>>>>
>>>>>>> We cannot call efi_disk_create() within blk_create_device() because
>>>>>>> some data fields of struct blk_desc, which are to be used by efi disk,
>>>>>>> are initialized *after* blk_create_device() in driver side.
>>>>>>>
>>>>>>> So we need to add a hook at/after every occurrence of blk_create_device()
>>>>>>> on driver side. For example,
>>>>>>>
>>>>>>> === drivers/scsi/scsi.c ===
>>>>>>> int do_scsi_scan_one(struct udevice *dev, int id, int lun, bool verbose)
>>>>>>> {
>>>>>>> ...
>>>>>>> ret = blk_create_devicef(dev, "scsi_blk", str, IF_TYPE_SCSI, -1,
>>>>>>> bd.blksz, bd.lba, &bdev);
>>>>>>> ...
>>>>>>> bdesc = dev_get_uclass_platdata(bdev);
>>>>>>> bdesc->target = id;
>>>>>>> bdesc->lun = lun;
>>>>>>> ...
>>>>>>>
>>>>>>> /*
>>>>>>> * We need have efi_disk_create() called here because bdesc->target
>>>>>>> * and lun will be used by dp helpers in efi_disk_add_dev().
>>>>>>> */
>>>>>>> efi_disk_create(bdev);
>>>>>>> }
>>>>>>>
>>>>>>> int scsi_scan_dev(struct udevice *dev, bool verbose)
>>>>>>> {
>>>>>>> for (i = 0; i < uc_plat->max_id; i++)
>>>>>>> for (lun = 0; lun < uc_plat->max_lun; lun++)
>>>>>>> do_scsi_scan_one(dev, i, lun, verbose);
>>>>>>> ...
>>>>>>> }
>>>>>>>
>>>>>>> int scsi_scan(bool verbose)
>>>>>>> {
>>>>>>> ret = uclass_get(UCLASS_SCSI, &uc);
>>>>>>> ...
>>>>>>> uclass_foreach_dev(dev, uc)
>>>>>>> ret = scsi_scan_dev(dev, verbose);
>>>>>>> ...
>>>>>>> }
>>>>>>> === ===
>>>>>>>
>>>>>>> Since scsn_scan() can be directly called by "scsi rescan" command,
>>>>>>> There seems to be no generic hook, or event, available in order to
>>>>>>> call efi_disk_create().
>>>>>>>
>>>>>>> Do I miss anything?
>>>>>>
>>>>>> Could the event handler that gets called from somewhere around
>>>>>> blk_create_device() just put it into an efi internal "todo list" which
>>>>>> we then process using an efi event?
>>>>>>
>>>>>> EFI events will only get triggered on the next entry to efi land, so by
>>>>>> then we should be safe.
>>>>>
>>>>> I think I now understand your suggestion; we are going to invent
>>>>> a specialized event-queuing mechanism so that we can take any actions
>>>>> later at appropriate time (probably in efi_init_obj_list()?).
>>>>
>>>> Uh, not sure I follow. There would be 2 events. One from the u-boot block layer to the efi_loader disk layer.
>>>
>>> This is a to-be-invented "specialized event-queuing mechanism"
>>> in my language :) as we cannot use efi_create/signal_event() before
>>> initializing EFI environment.
>>>
>>> This event will be expected to be 'signal'ed at every creation/deletion
>>> of UCLASS_BLK device. Right?
>>
>> Correct.
>>
>>>
>>>> That event handler creates a new efi event (like a timer w/ timeout=0).
>>>
>>> But when is this event handler fired?
>>> I think the only possible timing is at efi_init_obj_list().
>>
>> We already walk through the event list on any u-boot/efi world switch.
>
> ? Where is the code?

Ah, I must have misremembered, sorry. I think that was one proposed
patch a while ago, but we didn't put it in.

But worst case we can just put additional efi_timer_check() calls at
strategic places if needed.

>
>>>
>>>> This new event's handler can then create the actual efi block device.
>>>
>>> I assume that this event handler is fired immediately after
>>> efi_signal_event() with timeout=0.
>>
>> Right, and that signal_event() will happen the next time we go back into efi land. By that time, the dm blk struct will be complete.
>
> This will be true.
>
>>>
>>> If so, why do we need to create an efi event? To isolate the disk code
>>> from the other init code?
>>
>> I don't think we should call init code during runtime, yes. These are 2 paths.
>>
>>>
>>> (If so, for the same reason, we should re-write efi_init_obj_list()
>>> with events for other efi resources as well.)
>>>
>>>>>
>>>>> But if so, it's not much different from my current approach where
>>>>> a list of efi disks are updated in efi_init_obj_list() :)
>>>>
>>>> The main difference is that disk logic stays in the disc code scope :).
>>>
>>> My efi_disk_update() (and efi_disk_register()) is the only function
>>> visible outside the disk code, isn't it?
>>>
>>> Using some kind of events here is smart, but looks to me a bit overdoing
>>> because we anyhow have to go through all the UCLASS_BLK devices to mark
>>> whether they are still valid or not :)
>>
>> What do you mean?
>
> "all the UCLASS_BLK deivces" -> all efi_disk_obj's
>
> Let me rephrase it;
> all efi_disk_obj's will be re-visisted in efi_init_obj_list() to determine
> its backing u-boot block device is still valid.
> If not valid, a said efi_disk_obj should be marked so to prevent further
> accessing in efi world.

Correct.

Alex