Messages in this thread | | | Date | Thu, 5 Jan 2023 08:50:17 +0100 | Subject | Re: [PATCH v2 1/2] usb: misc: onboard_usb_hub: Don't create platform devices for DT nodes without 'vdd-supply' | From | Stefan Wahren <> |
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Hi Matthias,
Am 04.01.23 um 20:37 schrieb Matthias Kaehlcke: > On Wed, Jan 04, 2023 at 10:00:43AM +0100, Alexander Stein wrote: >> Hi Matthias, >> >> Am Dienstag, 3. Januar 2023, 18:12:24 CET schrieb Matthias Kaehlcke: >>> On Thu, Dec 22, 2022 at 11:26:26AM -0800, Doug Anderson wrote: >>>> Hi, >>>> >>>> On Wed, Dec 21, 2022 at 6:26 PM Matthias Kaehlcke <mka@chromium.org> >> wrote: >>>>> The primary task of the onboard_usb_hub driver is to control the >>>>> power of an onboard USB hub. The driver gets the regulator from the >>>>> device tree property "vdd-supply" of the hub's DT node. Some boards >>>>> have device tree nodes for USB hubs supported by this driver, but >>>>> don't specify a "vdd-supply". This is not an error per se, it just >>>>> means that the onboard hub driver can't be used for these hubs, so >>>>> don't create platform devices for such nodes. >>>>> >>>>> This change doesn't completely fix the reported regression. It >>>>> should fix it for the RPi 3 B Plus and boards with similar hub >>>>> configurations (compatible DT nodes without "vdd-supply"), boards >>>>> that actually use the onboard hub driver could still be impacted >>>>> by the race conditions discussed in that thread. Not creating the >>>>> platform devices for nodes without "vdd-supply" is the right >>>>> thing to do, independently from the race condition, which will >>>>> be fixed in future patch. >>>>> >>>>> Fixes: 8bc063641ceb ("usb: misc: Add onboard_usb_hub driver") >>>>> Link: >>>>> https://lore.kernel.org/r/d04bcc45-3471-4417-b30b-5cf9880d785d@i2se.com >>>>> / Reported-by: Stefan Wahren <stefan.wahren@i2se.com> >>>>> Signed-off-by: Matthias Kaehlcke <mka@chromium.org> >>>>> --- >>>>> >>>>> Changes in v2: >>>>> - don't create platform devices when "vdd-supply" is missing, >>>>> >>>>> rather than returning an error from _find_onboard_hub() >>>>> >>>>> - check for "vdd-supply" not "vdd" (Johan) >>>>> - updated subject and commit message >>>>> - added 'Link' tag (regzbot) >>>>> >>>>> drivers/usb/misc/onboard_usb_hub_pdevs.c | 13 +++++++++++++ >>>>> 1 file changed, 13 insertions(+) >>>> I'm a tad bit skeptical. >>>> >>>> It somehow feels a bit too much like "inside knowledge" to add this >>>> here. I guess the "onboard_usb_hub_pdevs.c" is already pretty >>>> entangled with "onboard_usb_hub.c", but I'd rather the "pdevs" file >>>> keep the absolute minimum amount of stuff in it and all of the details >>>> be in the other file. >>>> >>>> If this was the only issue though, I'd be tempted to let it slide. As >>>> it is, I'm kinda worried that your patch will break Alexander Stein, >>>> who should have been CCed (I've CCed him now) or Icenowy Zheng (also >>>> CCed now). I believe those folks are using the USB hub driver >>>> primarily to drive a reset GPIO. Looking at the example in the >>>> bindings for one of them (genesys,gl850g.yaml), I even see that the >>>> reset-gpio is specified but not a vdd-supply. I think you'll break >>>> that? >>> Thanks for pointing that out. My assumption was that the regulator is >>> needed for the driver to do anything useful, but you are right, the >>> reset GPIO alone could be used in combination with an always-on regulator >>> to 'switch the hub on and off'. >>> >>>> In general, it feels like it should actually be fine to create the USB >>>> hub driver even if vdd isn't supplied. Sure, it won't do a lot, but it >>>> shouldn't actively hurt anything. You'll just be turning off and on >>>> bogus regulators and burning a few CPU cycles. I guess the problem is >>>> some race condition that you talk about in the commit message. I'd >>>> rather see that fixed... >>> Yes, the race conditions needs to be fixed as well, I didn't have enough >>> time to write and test a patch before taking a longer break for the >>> holidays, so I only sent out this (supposed) partial mitigation. >>> >>>> That being said, if we want to be more efficient and not burn CPU cycles >>>> and memory in Stefan Wahren's case, maybe the USB hub driver itself could >>>> return a canonical error value from its probe when it detects that it has >>>> no useful job and then "onboard_usb_hub_pdevs" could just silently bail >>>> out? >>> _probe() could return an error, however onboard_hub_create_pdevs() can't >>> rely on that, since the actual onboard_hub driver might not have been >>> loaded yet when the function is called. >>> >>> It would be nice not to instantiate the pdev and onboard_hub USB instances >>> if the DT node has neither a 'vdd-supply' nor 'reset-gpios'. If we aren't >>> ok with doing that in onboard_hub_create_pdevs() then at least the 'raw' >>> platform device would be created. onboard_hub_probe() could still >>> bail if both properties are absent, _find_onboard_hub() would have to >>> check it again to avoid the deferred probing 'loop' for the USB instances. >> I'm not really fond of checking for optional features like 'vdd-supply' and >> 'reset-gpios'. This issue will pop up again if some new optional feature is >> added again, e.g. power-domains. > It's not just any optional feature, it needs to be involved in controlling > power. I'm not super-exited about it either, but if we prefer not to > instantiate the drivers for certain DT nodes (TBD if that's a preference), we > need some sort of sentinel since the compatible string alone doesn't provide > enough information. > >>> Alternatively we could 'just' fix the race condition involving the 'attach >>> work' and the onboard_hub driver is fully instantiated even on (certain) >>> boards where it does nothing. It's relatively rare that USB hub nodes are >>> specified in the DT (unless the intention is to use this driver) and >>> CONFIG_USB_ONBOARD_HUB needs to be set for the instances to be created, >>> so maybe creating the useless instances is not such a big deal. >> IMHO creating a pdev shouldn't harm in any case. It's similar to having a DT >> node without a corresponding driver enabled or even existing. > If we only want a 'raw' pdev (no instantiation of the onboard hub platform and > USB drivers) then a similar logic will be needed in the onboard hub driver(s). > > So if we don't want any logic checking that at least one power related property > is defined then we have to accept that the onboard hub driver will be fully > instantiated even when it effectively does nothing. > > If we add logic to the driver it needs to be checked in both the platform and > the USB driver (in the latter to avoid a deferred probe loop). It would be > simpler to just skip the creation of the 'raw' platform device in the first > place. > >> Also adding USB devices to DT is something which is to be expected. >> usb-device.yaml exists since 2020 and the txt version since 2016. > Yes it it perfectly legal, so we need to handle this case somehow, and we > are currently discussing how to best do that :) > > I still don't expect the combo of supported hub in the DT + > CONFIG_USB_ONBOARD_HUB=y/m to become super-popular, which could be an > argument for the option "just instantiate the drivers even if they do > nothing". Not my favorite option, but probably not that bad either.
i disagree in this point. The driver becomes more and more popular [1] and this breaks arm64 for RPi 3B+ too. So it's only a question of time until distributions run into this problem.
I willing to help in debugging the real issue, but i need a little bit guidance here.
[1] - https://lore.kernel.org/linux-arm-kernel/2188024.ZfL8zNpBrT@steina-w/T/
> >> Unfortunately I'm not able to reproduce this issue on a different platform >> where the same HUB but no reset-gpios is required. I also noticed that >> onboard-usb-hub raises the error >>> Failed to attach USB driver: -22 >> for each hub it is supposed to support. > Interesting > > I also see the error with v6.2-rc1 but not a downstream v5.15 kernel which > runs most of the time on my boards. It turns out that with v6.2-rc1 the 'bus' > field of 'onboard_hub_usbdev_driver.drvwrap.driver' (passed to driver_attach()) > is NULL, which causes driver_attach() / bus_for_each_dev() to return -EINVAL. > > I did some testing (unbind/bind, unloading/reloading the driver) around the > 'attach work' independently from your report. I couldn't repro a situation > where the onboard_hub USB devices aren't probed by the driver, which is what > the 'attach work' is supposed to solve. At some point I observed issues with > that in the past, which is why driver_attach() is called. The driver_attach() > call was added to the onboard_hub series in early 2021, by that time I was > probably testing with a v5.4 kernel, it's not unconceivable that the issue I > saw back then is fixed in newer kernels. > > With that I was already considering to remove the 'attach work', the error you > reported reinforces that, since the driver_attach() call from the onboard_hub > driver does nothing in more recent kernels due to 'bus' being NULL. > > Thanks > > Matthias
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