Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 2 Jan 2023 12:44:33 +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 <> |
| |
Hello Alexander,
Am 02.01.23 um 10:20 schrieb Alexander Stein: > Hi everybody, > > Am Freitag, 23. Dezember 2022, 08:46:45 CET schrieb Icenowy Zheng: >> 在 2022-12-22星期四的 11:26 -0800,Doug Anderson写道: >> >>> 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? >> Well technically in my final DT a regulator is included (to have the >> Vbus enabled when enabling the hub), however I am still against this >> patch, because the driver should work w/o vdd-supply (or w/o reset- >> gpios), and changing this behavior is a DT binding stability breakage. > I second that. The bindings don't require neither vdd-supply nor reset-gpios. > > But I have to admit I lack to understand the purpose of this series in the > first place. What is the benefit or fix?
did you followed the provided link from the patch?
Best regards
> > Best regards, > Alexader > >> In addition the kernel never fails because of a lacking regulator >> unless explicitly forbid dummy regulators. >> >> BTW USB is a discoverable bus, and if a hub do not need special >> handlement, it just does not need to appear in the DT, thus no onboard >> hub DT node. >> >>> 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... 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? >> I agree. > > >
| ![\](/images/icornerr.gif) |