On Fri, Sep 3, 2021 at 3:16 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > On Thu, Sep 2, 2021 at 5:53 PM Rob Herring <robh+dt@xxxxxxxxxx> wrote: > > > > On Thu, Sep 2, 2021 at 2:29 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > > > > > On Thu, Sep 2, 2021 at 12:03 PM Rob Herring <robh+dt@xxxxxxxxxx> wrote: > > > > > > > > On Thu, Sep 2, 2021 at 11:57 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > > > > > > > > > On Thu, Sep 2, 2021 at 7:24 AM Rob Herring <robh+dt@xxxxxxxxxx> wrote: > > > > > > > > > > > > On Wed, Sep 1, 2021 at 9:55 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > We don't want fw_devlink creating device links for bus devices as > > > > > > > they'll never probe. So mark those device node with this flag. > > > > > > > > > > > > > > Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx> > > > > > > > --- > > > > > > > drivers/of/platform.c | 16 ++++++++++++++++ > > > > > > > 1 file changed, 16 insertions(+) > > > > > > > > > > > > > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c > > > > > > > index 74afbb7a4f5e..42b3936d204a 100644 > > > > > > > --- a/drivers/of/platform.c > > > > > > > +++ b/drivers/of/platform.c > > > > > > > @@ -392,6 +392,22 @@ static int of_platform_bus_create(struct device_node *bus, > > > > > > > if (!dev || !of_match_node(matches, bus)) > > > > > > > return 0; > > > > > > > > > > > > > > + /* > > > > > > > + * If the bus node has only one compatible string value and it has > > > > > > > + * matched as a bus node, it's never going to get probed by a device > > > > > > > + * driver. So flag it as such so that fw_devlink knows not to create > > > > > > > + * device links with this device. > > > > > > > + * > > > > > > > + * This doesn't catch all devices that'll never probe, but this is good > > > > > > > + * enough for now. > > > > > > > + * > > > > > > > + * This doesn't really work for PPC because of how it uses > > > > > > > + * of_platform_bus_probe() to add normal devices. So ignore PPC cases. > > > > > > > + */ > > > > > > > + if (!IS_ENABLED(CONFIG_PPC) && > > > > > > > + of_property_count_strings(bus, "compatible") == 1) > > > > > > > + bus->fwnode.flags |= FWNODE_FLAG_NOT_DEVICE; > > > > > > > > > > > > This looks fragile relying on 1 compatible string, and the DT flags in > > > > > > this code have been fragile too. I'm pretty sure we have cases of > > > > > > simple-bus or simple-mfd that also have another compatible. > > > > > > > > > > > > Couldn't we solve this with a simple driver? > > > > > > > > > > Oh, I didn't think you'd like that. I'd lean towards that option too > > > > > if we can address some of the other concerns below. > > > > > > > > > > > Make 'simple-pm-bus' > > > > > > driver work for other cases? > > > > > > > > > > > BTW, this patch doesn't even work for > > > > > > simple-pm-bus. > > > > > > > > > > How do you mean? Because simple-pm-bus already has a driver and > > > > > doesn't set "matches" param when it calls of_platform_populate() and > > > > > this flag won't be set. So at least for simple-pm-bus I don't see any > > > > > issue. > > > > > > > > You're right. > > > > > > > > > I was trying to reuse of_default_bus_match_table without explicitly > > > > > referring to it, but if it's confusing I can add a separate list of > > > > > compatible strings and use those here instead of using "matches". > > > > > > > > What happens with a non-default table? I'm not sure we can assume the > > > > same behavior. > > > > > > > > > > A driver for simple-bus may cause issues if there's a > > > > > > more specific driver to bind to as we don't handle that. It's simply > > > > > > whichever matches first. > > > > > > > > > > Right, this is my worry. Especially for devices like this (there are > > > > > plenty of cases like this) which have a driver that probes them but > > > > > also lists simple-bus > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/arm-realview-pb11mp.dts?id=73f3af7b4611d77bdaea303fb639333eb28e37d7#n299 > > > > > > > > Uhh, that one is certainly a leakage of wanting an soc_device in the > > > > hierarchy, not any real bus structure reflecting the h/w. I'm not a > > > > fan of the soc_device stuff and its optional nature. Everything is an > > > > SoC, so it should always be there? Or your device hierarchy should > > > > change when you decide to add a soc_device? > > > > > > > > > So as long as there's a compatible string that's not one of the > > > > > "transparent" busses, this driver shouldn't match. So, I don't think I > > > > > can get away from checking the compatible strings. > > > > > > > > > > How about I check here to make sure all the "compatible" strings are > > > > > from an approved transparent bus list, and if it's true, I use > > > > > driver_override to force match it to a transparent bus driver? Would > > > > > you be okay with that? > > > > > > > > Can't we do that within a driver? We check this and fail probe if > > > > there's a more specific compatible. Then another driver can match and > > > > probe. > > > > > > I was thinking that initially, but if we fail a probe, the driver core > > > will permanently give up (won't search further) or might end up > > > retrying with the same driver and never get to the other driver. I'll > > > send out a v2 with what I described above. It's not too bad and it > > > will also allow us to handle the PPC cases (we'll just need to keep > > > adding the simple-bus equivalent entries to a table). > > > > I wasn't sure, but I traced the calls and it looks like based on > > __driver_attach() that if a driver fails probe another one matching > > should get to probe: > > __driver_attach() is called over every device already in a bus. It's > called only when a new driver is registered. So it makes sense that > one ignores the error returned from probe(). You don't want to fail > driver registration because one specific device needs to defer probe. > > The comment is actually from __device_attach_driver() > > > > > /* > > * Ignore errors returned by ->probe so that the next driver can try > > * its luck. > > */ > > I saw that comment too, but isn't the comment wrong/stale? > > bus_probe_device() -> device_initial_probe() -> __device_attach(). > > In __device_attach() we have: > ret = bus_for_each_drv(dev->bus, NULL, &data, __device_attach_driver); > > If you look at bus_for_each_drv()'s comment: > * ...... If @fn returns anything but 0, we break out > * and return it. If @start is not NULL, we use it as the head > * of the list. > > Inside __device_attach_driver() we see: > /* > * Ignore errors returned by ->probe so that the next driver can try > * its luck. > */ > ret = driver_probe_device(drv, dev); > if (ret < 0) > return ret; > > So if probe() returned an error, we'd return it right back out. And > then bus_for_each_drv() will stop searching for more drivers that > match. Well, not quite. If ->probe() returns an error, really_probe() will convert it into a positive number. __driver_probe_device() will then return as is and driver_probe_device() doesn't touch that value. Bottom line: you'll see a positive number here, so the check above will not trigger and 0 is returned, so bus_for_each_drv() will actually continue searching. > So I don't think one driver can give up after a match and have another > driver give a device a shot. Yes, it can.
