On Thu, Jul 22, 2021 at 01:09:05PM -0700, John Stultz wrote: > On Thu, Jul 22, 2021 at 12:17 PM Bjorn Andersson > <bjorn.andersson@xxxxxxxxxx> wrote: > > > On Jul 21, 2021, 1:45 PM +0200, Krzysztof Kozlowski wrote: > > > > 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. > > > > > > > > Really, all normal systems depend on aliases or names and here we have > > > > dependency on device address. I proposed way how AOSP should be fixed. > > > > Anything happened? Nope. > > > > > > First time he sent a possible solution for the problem: > > > https://lore.kernel.org/lkml/20201221210423.GA2504@kozik-lap/ > > > > > > To sum up you could have used one of the more portable approaches > > > 1. add an udc alias to the controller and use it then to refer to the > > > corresponding USB controller > > > > Is there such a thing as "UDC alias"? Or are you suggesting that we > > should add such feature? > > > > I think it would be wonderful if we could identify the UDCs on our > > boards as "USB1" and "USB2", or "the one and only USB-C connector". But > > unless that will fall back to the existing naming it would break John's > > _existing_ userspace. > > Well, I'd not hold up the existing userspace I'm using as sacrosanct > (AOSP devices still usually don't have to work cross-kernel versions - > devboards being the main exception). I'm fine if we can rework > userland as proposed, so that the issues can be avoided, but I > honestly don't have enough context to really understand what that > looks like (no idea what udc aliases are). > > And whatever we do, the main constraint is that userland has to be > able to work with existing LTS kernels and newer kernels. As I said in my response to Bjorn even if it is added to the kernel it won't get to the official LTSes as it would be a new kernel feature. New features aren't normally backported to the older kernels. > > > > 2. search through DT-nodes looking for a specific compatible/reg > > > DT-properties. > > > > > > > We could define that this is the way, but again we didn't yesterday so > > your proposal is not backwards compatible. > > It may be backwards compatible, but I'm still not clear exactly how it > would work. > > I guess if we look through all > sys/bus/platform/devices/*/of_node/compatbile strings for the desired > "snps,dwc3", then find which of the directories have the desired > address in the string? (The suggestion for looking at reg seems > better, but I don't get a char value out of the dwc3 of_node/reg > file). The algorithm is simple: 1) You know what USB controllers you have on your platform. They are supposed to be compatible with snps,dwc3 string and have some pre-defined base address. 2) Find all the files in the directory /sys/class/udc/. 3) Walk through all the directories in /sys/bus/platform/devices/ with names found in 2) and stop on the device with matching compatible/base address defined in 1). In my case the strings could be retrieved like this: USB_NAME_COMPAT=$(/sys/bus/platform/devices/1f100000.usb/of_node/compatible | tr '\0' '\t' | cut -f1) USB_DEVICE_ADDR="$(head -c 4 /sys/bus/platform/devices/1f100000.usb/of_node/reg | hexdump -ve '/1 "%02x"' | sed -e 's/^0*//g')" Regards, -Sergey > > It seems much more straightforward to do an `ls /sys/class/udc/$GADGET_ADDR.*` > > But again, if folks decide the names can be rearranged to usb.<addr> > in the future, that would break too. > > thanks > -john
