Hi Pawel, Pawel Laszczak <pawell@xxxxxxxxxxx> writes: >>Pawel Laszczak <pawell@xxxxxxxxxxx> writes: >>> From: Pawel Laszczak <pawell@xxxxxxxxxxx> >>> >>> Patch adds disabling endpoint before enabling it during changing >>> alternate setting. Lack of this functionality causes that in some >>> cases uac2 queue the same request multiple time. >>> Such situation can occur when host send set interface with >>> alternate setting 1 twice. >> >>Which host is doing that? > > I've found out this issue on different scenario, but we can imaging the case with double alternate setting. > > My case looks like: > - host send Set Alternate Interface (1) > - device controller doesn't send ACK for SETUP packet > - device delegates request to class and class starts processing it (enable endpoints, etc.) > - in the meantime host re-send the same SETUP packet > - device controller driver detects this packet and try to finish previous one (according to USB spec), but it cannot disable enabled endpoints. > - device delegate the new SETUP packet to uac2 class > - uac2 again enables endpoint and try to queues again queued requests > - system crash > > The similar solution exist in f_uvc.c: > https://elixir.bootlin.com/linux/v5.12-rc8/source/drivers/usb/gadget/function/f_uvc.c#L290 > > I didn't check the other drivers. Maybe such fix should be added somewhere else. > > Such issue can be very rare and very hard to debug. yeah, this is a requirement by the spec, IIRC. A SetAlt to the same interface/altSetting means the host wants to reset that altSetting. From the peripheral point of view that means disabling the endpoints and reenabling them. I'm just not entirely sure if we should do this in u_audio or f_uac[12].c. Arguably, composite.c could detect this and disable the altSetting, but that would require a huge refactor on the framework. My gut feeling is that for the minimal bug fix, we should patch f_uac[12].c, but all audio function drivers have the same exact bug, so I don't know. If we follow the "standard" of patching the relevant set_alt functions in the function drivers, the moment we decide to go for a refactoring, it'll be easier to see common constructs. -- balbi
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