On Sun 15 Aug 14:46 CDT 2021, Serge Semin wrote: > Hello John > > On Fri, Aug 13, 2021 at 06:06:24PM -0700, John Stultz wrote: > > On Thu, Jul 22, 2021 at 3:09 PM Serge Semin <fancer.lancer@xxxxxxxxx> wrote: > > > 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')" > > > > > > > Hey Serge, > > I just wanted to follow up here. Amit has reworked the db845c AOSP > > userland so that it no longer uses the fixed node name, but instead > > probes for it: > > https://android-review.googlesource.com/c/device/linaro/dragonboard/+/1774872 > > > > Admittedly, it does take a short-cut. As your algorithm above, > > digging up the devices and finding the sys/bus path to read the reg > > value and pipe through hexdump (which android doesn't have) seemed > > overly obtuse when the address is in the node name itself (while the > > only way to be sure, one normally doesn't use spectroscopy to > > determine the value of a coin when you can read what's printed on it > > :). But, should the node naming be further changed at least the > > infrastructure we have can be reworked fairly easily to adapt now. > > > > In any case, as we can handle the name change now, if you want to > > resubmit your patch, we would no longer object (but can't promise no > > one else might be bitten). Sorry for the delay this caused, and we > > appreciate you working with us to find a solution. > > Great! Thanks for sending the notification. I'll resend the patch with a > reference to your report and to the update made to AOSP, as soon as I > am done with my current task. > Amit's change makes future versions of AOSP able to cope with changes in the UDC name, unfortunately it doesn't change the fact that renaming the node breaks compatibility in non-Android user space (or any existing branches/tags of AOSP). Regards, Bjorn
