On Wed, Jul 21, 2021 at 01:10:19PM +0200, Krzysztof Kozlowski wrote: > On 21/07/2021 13:02, Greg Kroah-Hartman wrote: > > On Wed, Jul 21, 2021 at 12:45:32PM +0200, Krzysztof Kozlowski wrote: > >> On 21/07/2021 12:29, Greg Kroah-Hartman wrote: > >>> On Wed, Jul 21, 2021 at 01:02:20PM +0300, Serge Semin wrote: > >>>> Hi Greg, > >>>> @Krzysztof, @Rob, please join the discussion so to finally get done > >>>> with the concerned issue. > >>>> > >>>> On Wed, Jul 21, 2021 at 09:38:54AM +0200, Greg Kroah-Hartman wrote: > >>>>> On Wed, Jul 14, 2021 at 03:48:07PM +0300, Serge Semin wrote: > >>>>>> Hello John, > >>>>>> > >>>>>> On Tue, Jul 13, 2021 at 05:07:00PM -0700, John Stultz wrote: > >>>>>>> On Tue, Oct 20, 2020 at 5:10 AM Serge Semin > >>>>>>> <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> wrote: > >>>>>>>> > >>>>>>>> In accordance with the DWC USB3 bindings the corresponding node > >>>>>>>> name is suppose to comply with the Generic USB HCD DT schema, which > >>>>>>>> requires the USB nodes to have the name acceptable by the regexp: > >>>>>>>> "^usb(@.*)?" . Make sure the "snps,dwc3"-compatible nodes are correctly > >>>>>>>> named. > >>>>>>>> > >>>>>>>> Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> > >>>>>>> > >>>>>> > >>>>>>> I know folks like to ignore this, but this patch breaks AOSP on db845c. :( > >>>>>> > >>>>>> Sorry to hear that. Alas there is no much can be done about it. > >>>>> > >>>>> Yes there is, we can revert the change. We do not break existing > >>>>> configurations, sorry. > >>>> > >>>> By reverting this patch we'll get back to the broken dt-bindings > >>>> since it won't comply to the current USB DT-nodes requirements > >>>> which at this state well describe the latest DT spec: > >>>> https://github.com/devicetree-org/devicetree-specification/releases/tag/v0.3 > >>>> Thus the dtbs_check will fail for these nodes. > >>>> > >>>> Originally this whole patchset was connected with finally getting the > >>>> DT-node names in order to comply with the standard requirement and it > >>>> was successful mostly except a few patches which still haven't been > >>>> merged in. > >>>> > >>>> Anyway @Krzysztof has already responded to the complain regarding this > >>>> issue here: > >>>> https://lore.kernel.org/lkml/20201221210423.GA2504@kozik-lap/ > >>>> but noone cared to respond on his reasonable questions in order to > >>>> get to a suitable solution for everyone. Instead we are > >>>> getting another email with the same request to revert the changes. > >>>> Here is the quote from the Krzysztof email so we could continue the > >>>> discussion: > >>>> > >>>> On Mon, 21 Dec 2020 13:04:27 -0800 (PST), Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote: > >>>>> On Mon, Dec 21, 2020 at 12:24:11PM -0800, John Stultz wrote: > >>>>>> On Sat, Dec 19, 2020 at 3:06 AM Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote: > >>>>>>> ... > >>>>>>> > >>>>>>> The node names are not part of an ABI, are they? I expect only > >>>>>>> compatibles and properties to be stable. If user-space looks for > >>>>>>> something by name, it's a user-space's mistake. Not mentioning that you > >>>>>>> also look for specific address... Imagine remapping of addresses with > >>>>>>> ranges (for whatever reason) - AOSP also would be broken? Addresses are > >>>>>>> definitely not an ABI. > >>>>>> > >>>>>> Though that is how it's exported through sysfs. > >>>>> > >>>>> The ABI is the format of sysfs file for example in /sys/devices. However > >>>>> the ABI is not the exact address or node name of each device. > >>>>> > >>>>>> In AOSP it is then used to setup the configfs gadget by writing that > >>>>>> value into /config/usb_gadget/g1/UDC. > >>>>>> > >>>>>> Given there may be multiple controllers on a device, or even if its > >>>>>> just one and the dummy hcd driver is enabled, I'm not sure how folks > >>>>>> reference the "right" one without the node name? > >>>>> > >>>>> I think it is the same type of problem as for all other subsystems, e.g. > >>>>> mmc, hwmon/iio. They usually solve it either with aliases or with > >>>>> special property with the name/label. > >>>>> > >>>>>> I understand the fuzziness with sysfs ABI, and I get that having > >>>>>> consistent naming is important, but like the eth0 -> enp3s0 changes, > >>>>>> it seems like this is going to break things. > >>>>> > >>>>> One could argue whether interface name is or is not ABI. But please tell > >>>>> me how the address of a device in one's representation (for example DT) > >>>>> is a part of a stable interface? > >>>>> > >>>>>> Greg? Is there some better way AOSP should be doing this? > >>>>> > >>>>> If you need to find specific device, maybe go through the given bus and > >>>>> check compatibles? > >>>>> > >>>>> Best regards, > >>>>> Krzysztof > >>>> > >>>> So the main question is how is the DT-node really connected with ABI > >>>> and is supposed to be stable in that concern? > >>>> > >>>> As I see it even if it affects the configfs node name, then we may > >>>> either need to break that connection and somehow deliver DT-node-name > >>>> independent interface to the user-space or we have no choice but to > >>>> export the node with an updated name and ask of user-space to deal > >>>> with it. In both suggested cases the DT-node name will still conform > >>>> to the USB-node name DT spec. Currently we are at the second one. > >>> > >>> I really do not care what you all decide on, but you CAN NOT break > >>> existing working systems, sorry. That is why I have reverted this > >>> change in my tree and will send it to Linus soon. > >> > >> I had impression that kernel defines interfaces which should be used and > >> are stable (e.g. syscalls, sysfs and so on). This case is example of > >> user-space relying on something not being marked as part of ABI. Instead > >> they found something working for them and now it is being used in "we > >> cannot break existing systems". Basically, AOSP unilaterally created a > >> stable ABI and now kernel has to stick to it. > > > > Since when are configfs names NOT a user-visable api? > > > > Why would you not depend on them? > > It's not good example. The configfs entries (file names) are > user-visible however the USB gadget exposes specific value for specific > one device. It encodes device specific DT node name and HW address and > gives it to user-space. It is valid only on this one HW, all other > devices will have different values. > > User-space has hard-coded this value (DT node name and hardware > address). This value was never part of configfs ABI, maybe except of its > format "[a-z]+\.[0-9a-f]+". Format is not broken. Just the value changes > for a specific device/hardware. > > It's like you depend that lsusb will always report: > Bus 003 Device 008: ID 046d:c52b Logitech, Inc. Unifying Receiver > and then probing order changed and this Logitech ends as Device 009. > Then AOSP guys come, wait, we hard-coded that Logitech on our device > will be always Device 008, not 009. Please revert it, we depend on > specific value of Device number. It must be always 009... > > For the record - the change discussed here it's nothing like USB VID/PID. :) Right I was wrong referring to the configfs names in this context. That must have mislead Greg. Getting back to the topic AFAICS from what John said in here https://lore.kernel.org/lkml/CALAqxLWGujgR7p8Vb5S_RimRVYxwm5XF-c4NkKgMH-43wEBaWg@xxxxxxxxxxxxxx/ AOSP developers somehow hardcoded a USB-controller UDC name in the internal property called "sys.usb.controller" with a value "ff100000.dwc3". That value is generated by the kernel based on the corresponding DT-node name. The property is then used to pre-initialize the system like it's done here: https://android.googlesource.com/platform/system/core/+/master/rootdir/init.usb.configfs.rc Since we changed the DT-node name in the recent kernel, we thus changed the UDC controller name so AOSP init procedure now fails to bring up the Linux USB-gadget using on the older UDC name. UDC is supposed to be ff100000.usb now (after this patch has been merged in). What problems I see here: 1) the AOSP developers shouldn't have hard-coded the value but read from the /sys/class/udc/* directory and then decided which controller to use. As it's described for instance here: https://www.kernel.org/doc/Documentation/usb/gadget_configfs.txt 2) even if they hard-coded the value, then they should have used an older dts file for their platform, since DTS is more platform-specific, but not the kernel one. Even if a dts-file is supplied in the kernel it isn't supposed to have the node names unchanged from release to release. Regards, -Sergey > > Best regards, > Krzysztof
