On Fri, Mar 5, 2021 at 3:45 AM Marek Szyprowski <m.szyprow...@samsung.com> wrote: > > Hi Saravana, > > On 04.03.2021 20:51, Saravana Kannan wrote: > > The uevents generated for an amba device need PID and CID information > > that's available only when the amba device is powered on, clocked and > > out of reset. So, if those resources aren't available, the information > > can't be read to generate the uevents. To workaround this requirement, > > if the resources weren't available, the device addition was deferred and > > retried periodically. > > > > However, this deferred addition retry isn't based on resources becoming > > available. Instead, it's retried every 5 seconds and causes arbitrary > > probe delays for amba devices and their consumers. > > > > Also, maintaining a separate deferred-probe like mechanism is > > maintenance headache. > > > > With this commit, instead of deferring the device addition, we simply > > defer the generation of uevents for the device and probing of the device > > (because drivers needs PID and CID to match) until the PID and CID > > information can be read. This allows us to delete all the amba specific > > deferring code and also avoid the arbitrary probing delays. > > > > Cc: Rob Herring <r...@kernel.org> > > Cc: Ulf Hansson <ulf.hans...@linaro.org> > > Cc: John Stultz <john.stu...@linaro.org> > > Cc: Saravana Kannan <sarava...@google.com> > > Cc: Linus Walleij <linus.wall...@linaro.org> > > Cc: Sudeep Holla <sudeep.ho...@arm.com> > > Cc: Nicolas Saenz Julienne <nsaenzjulie...@suse.de> > > Cc: Geert Uytterhoeven <geert+rene...@glider.be> > > Cc: Marek Szyprowski <m.szyprow...@samsung.com> > > Cc: Russell King <li...@armlinux.org.uk> > > Signed-off-by: Saravana Kannan <sarava...@google.com> > > --- > > > > v1 -> v2: > > - Dropped RFC tag > > - Complete rewrite to not use stub devices. > > v2 -> v3: > > - Flipped the if() condition for hard-coded periphids. > > - Added a stub driver to handle the case where all amba drivers are > > modules loaded by uevents. > > - Cc Marek after I realized I forgot to add him. > > > > Marek, > > > > Would you mind testing this? It looks okay with my limited testing. > > It looks it works fine on my test systems. I've checked current > linux-next and this patch. You can add: > > Tested-by: Marek Szyprowski <m.szyprow...@samsung.com>
Hi Marek, Thanks! Does your test set up have amda drivers that are loaded based on uevents? That's the one I couldn't test. > I've briefly scanned the code and I'm curious how does it work. Does it > depend on the recently introduced "fw_devlink=on" feature? I don't see > other mechanism, which would trigger matching amba device if pm domains, > clocks or resets were not available on time to read pid/cid while adding > a device... No, it does not depend on fw_devlink or device links in any way. When a device is attempted to be probed (when it's added or during deferred probe), it's matched with all the drivers on the bus. When a new driver is registered to a bus, all devices in that bus are matched with the driver to see if they'll work together. That's how match is called. And match() can return -EPROBE_DEFER and that'll cause the device to be put in the deferred probe list by driver core. The tricky part in this patch was the uevent handling and the chicken-and-egg issue I talk about in the comments. Russell, Does this look good now? Plan to pick it up some time? Thanks, Saravana > > Best regards > -- > Marek Szyprowski, PhD > Samsung R&D Institute Poland >