Re: [PATCH v4 1/2] drivers: bus: simple-pm-bus: Add support for probing simple bus only devices

From: Abel Vesa
Date: Fri Nov 19 2021 - 11:17:06 EST

On 21-11-16 17:11:33, Abel Vesa wrote:
> On 21-11-16 15:59:11, Abel Vesa wrote:
> > On 21-11-15 12:17:46, Saravana Kannan wrote:
> > > On Wed, Nov 10, 2021 at 12:24 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
> > > >
> > > > On Wed, Nov 10, 2021 at 4:16 AM Abel Vesa <abelvesa@xxxxxxxxxx> wrote:
> > > > >
> > > > > On 21-09-28 17:07:33, Saravana Kannan wrote:
> > > > > > fw_devlink could end up creating device links for bus only devices.
> > > > > > However, bus only devices don't get probed and can block probe() or
> > > > > > sync_state() [1] call backs of other devices. To avoid this, probe these
> > > > > > devices using the simple-pm-bus driver.
> > > > > >
> > > > > > However, there are instances of devices that are not simple buses (they get
> > > > > > probed by their specific drivers) that also list the "simple-bus" (or other
> > > > > > bus only compatible strings) in their compatible property to automatically
> > > > > > populate their child devices. We still want these devices to get probed by
> > > > > > their specific drivers. So, we make sure this driver only probes devices
> > > > > > that are only buses.
> > > > > >
> > > > > > [1] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@xxxxxxxxxxxxxx/
> > > > > > Fixes: c442a0d18744 ("driver core: Set fw_devlink to "permissive" behavior by default")
> > > > > > Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
> > > > > > Tested-by: Saravana Kannan <saravanak@xxxxxxxxxx>
> > > > > > Tested-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> > > > > > ---
> > > > > > drivers/bus/simple-pm-bus.c | 42 ++++++++++++++++++++++++++++++++++---
> > > > > > 1 file changed, 39 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/bus/simple-pm-bus.c b/drivers/bus/simple-pm-bus.c
> > > > > > index 01a3d0cd08ed..6b8d6257ed8a 100644
> > > > > > --- a/drivers/bus/simple-pm-bus.c
> > > > > > +++ b/drivers/bus/simple-pm-bus.c
> > > > > > @@ -13,11 +13,36 @@
> > > > > > #include <linux/platform_device.h>
> > > > > > #include <linux/pm_runtime.h>
> > > > > >
> > > > > > -
> > > > > > static int simple_pm_bus_probe(struct platform_device *pdev)
> > > > > > {
> > > > > > - const struct of_dev_auxdata *lookup = dev_get_platdata(&pdev->dev);
> > > > > > - struct device_node *np = pdev->dev.of_node;
> > > > > > + const struct device *dev = &pdev->dev;
> > > > > > + const struct of_dev_auxdata *lookup = dev_get_platdata(dev);
> > > > > > + struct device_node *np = dev->of_node;
> > > > > > + const struct of_device_id *match;
> > > > > > +
> > > > > > + /*
> > > > > > + * Allow user to use driver_override to bind this driver to a
> > > > > > + * transparent bus device which has a different compatible string
> > > > > > + * that's not listed in simple_pm_bus_of_match. We don't want to do any
> > > > > > + * of the simple-pm-bus tasks for these devices, so return early.
> > > > > > + */
> > > > > > + if (pdev->driver_override)
> > > > > > + return 0;
> > > > > > +
> > > > > > + match = of_match_device(dev->driver->of_match_table, dev);
> > > > > > + /*
> > > > > > + * These are transparent bus devices (not simple-pm-bus matches) that
> > > > > > + * have their child nodes populated automatically. So, don't need to
> > > > > > + * do anything more. We only match with the device if this driver is
> > > > > > + * the most specific match because we don't want to incorrectly bind to
> > > > > > + * a device that has a more specific driver.
> > > > > > + */
> > > > > > + if (match && match->data) {
> > > > > > + if (of_property_match_string(np, "compatible", match->compatible) == 0)
> > > > > > + return 0;
> > > > > > + else
> > > > > > + return -ENODEV;
> > > > > > + }
> > > > >
> > > > > This change is breaking the expected behavior for the already existent
> > > > > simple-bus nodes. All the simple-bus compatibles should be replaced now
> > > > > to simple-pm-bus. In my case, on some i.MX8 platforms, without the
> > > > > devlink, the devices suspend sequence changes (and even breaks).
> > > > >
> > > > > To avoid breaking the already existent simple-bus nodes, maybe the logic
> > > > > should've been reversed: keep the simple-bus as is and add another
> > > > > compatible, IDK, something like simple-trasnparent-bus, or something.
> > > >
> > > > The intent of this change IS to affect existing simple-bus nodes (but
> > > > not in the way it's affecting you). But if it's breaking stuff, we
> > > > obviously need to fix it.
> > > >
> > > > I have a hunch on what's going on in your case, but can you point me
> > > > to the specific simple-bus node that's getting affected? I'm expecting
> > > > it to be a simple-bus node that gets added AFTER this driver is
> > > > registered at device_initcall (module_init gets converted to
> > > > device_initcall).
> > > >
> >
> > Well, for now, I can't pinpoint exactly one specific dts node.
> > My usecase is a little bit more complicated since it's only happening
> > in conjunction with a local change in the imx-mu-irq driver
> > in our local tree. Basically, the local change is forcing a suspend abort by
> > calling pm_system_wake if there is an irq from SCU triggered after the
> > suspend noirq imx-mu-irq driver callback has been called.
> > If we replace all the simple-bus with simple-pm-bus, everything works
> > fine.
> >
> > > > Also, can you try this hack patch to see if it helps your case?
> > > > https://lore.kernel.org/lkml/CAGETcx9U130Oq-umrvXME4JhEpO0Wadoki3kNxx=0-YvTR6PtQ@xxxxxxxxxxxxxx/
> > > >
> >
> > Nope, it doesn't work with this patch either.
> >
> > And the funny thing is, even if I add the pm_runtime_enable to your patch
> > like this:
> >
> > diff --git a/drivers/bus/simple-pm-bus.c b/drivers/bus/simple-pm-bus.c
> > index 6b8d6257ed8a..a13324fd700b 100644
> > --- a/drivers/bus/simple-pm-bus.c
> > +++ b/drivers/bus/simple-pm-bus.c
> > @@ -38,9 +38,11 @@ static int simple_pm_bus_probe(struct platform_device *pdev)
> > * a device that has a more specific driver.
> > */
> > if (match && match->data) {
> > - if (of_property_match_string(np, "compatible", match->compatible) == 0)
> > + if (of_property_match_string(np, "compatible", match->compatible) == 0) {
> > + pm_runtime_enable(&pdev->dev);
> > + of_platform_populate(np, NULL, lookup, &pdev->dev);
> > return 0;
> > - else
> > + } else
> > return -ENODEV;
> > }
> >
> > I get the following warning:
> >
> > [ 1.009392] ------------[ cut here ]------------
> > [ 1.013681] Enabling runtime PM for inactive device (bus@5d000000) with active children
> > [ 1.021721] WARNING: CPU: 3 PID: 1 at drivers/base/power/runtime.c:1439 pm_runtime_enable+0xc0/0x100
> > [ 1.030794] Modules linked in:
> > [ 1.033837] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.15.0-04906-gc0a8c67532b6-dirty #226
> > [ 1.042175] Hardware name: Freescale i.MX8QXP MEK (DT)
> > [ 1.047302] pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > [ 1.054248] pc : pm_runtime_enable+0xc0/0x100
> > [ 1.058594] lr : pm_runtime_enable+0xc0/0x100
> > [ 1.062938] sp : ffff800011e4bb60
> > [ 1.066237] x29: ffff800011e4bb60 x28: 0000000000000000 x27: ffff8000119204d0
> > [ 1.073361] x26: ffff8000119c1060 x25: ffff8000119c1078 x24: ffff80001190f0a0
> > [ 1.080484] x23: 0000000000000000 x22: 0000000000000000 x21: ffff0008006a00f4
> > [ 1.087608] x20: 0000000000000000 x19: ffff0008006a0010 x18: 0000000000000030
> > [ 1.094732] x17: 6974636120687469 x16: 7720293030303030 x15: 3064354073756228
> > [ 1.101856] x14: 2065636976656420 x13: ffff800011c21dc0 x12: 0000000000000246
> > [ 1.108981] x11: 00000000000000c2 x10: ffff800011c79dc0 x9 : 00000000fffff000
> > [ 1.116103] x8 : ffff800011c21dc0 x7 : ffff800011c79dc0 x6 : 0000000000000000
> > [ 1.123227] x5 : 000000000000bff4 x4 : 0000000000000000 x3 : 00000000ffffefff
> > [ 1.130351] x2 : ffff800011c21d30 x1 : 6bf7c63081c63600 x0 : 0000000000000000
> > [ 1.137478] Call trace:
> > [ 1.139910] pm_runtime_enable+0xc0/0x100
> > [ 1.143903] simple_pm_bus_probe+0x80/0xf0
> > [ 1.147986] platform_probe+0x6c/0xe0
> > [ 1.151637] really_probe.part.0+0x9c/0x310
> > [ 1.155805] __driver_probe_device+0x98/0x144
> > [ 1.160149] driver_probe_device+0xc8/0x15c
> > [ 1.164319] __driver_attach+0xfc/0x190
> > [ 1.168141] bus_for_each_dev+0x70/0xc0
> > [ 1.171964] driver_attach+0x28/0x3c
> > [ 1.175526] bus_add_driver+0x108/0x1f0
> > [ 1.179348] driver_register+0x7c/0x130
> > [ 1.183173] __platform_driver_register+0x2c/0x40
> > [ 1.187862] simple_pm_bus_driver_init+0x20/0x2c
> > [ 1.192466] do_one_initcall+0x54/0x1bc
> > [ 1.196289] kernel_init_freeable+0x210/0x294
> > [ 1.200633] kernel_init+0x28/0x130
> > [ 1.204110] ret_from_fork+0x10/0x20
> > [ 1.207678] ---[ end trace 719a02e69bfeb03f ]---
> >
> > though it should be behaving exactly like in the case of simple-pm-bus.
> >
> > Maybe I'm missing something here.
> >
> > I'll keep digging.
> >

Looking at this, it seems the devlinks are actually dropped after being
created:

[ 36.993371] Hardware name: Freescale i.MX8QXP MEK (DT)
[ 36.998498] Call trace:
[ 37.000928] dump_backtrace+0x0/0x19c
[ 37.004578] show_stack+0x1c/0x70
[ 37.007878] dump_stack_lvl+0x68/0x84
[ 37.011527] dump_stack+0x1c/0x38
[ 37.014826] __device_link_del+0x40/0xbc
[ 37.018738] device_link_drop_managed+0x74/0x90
[ 37.023253] device_links_driver_bound+0x1b4/0x280
[ 37.028031] driver_bound+0x68/0xd0
[ 37.031509] really_probe.part.0+0x258/0x310
[ 37.035763] __driver_probe_device+0x98/0x144
[ 37.040107] driver_probe_device+0xc8/0x15c
[ 37.044279] __driver_attach+0xfc/0x190
[ 37.048100] bus_for_each_dev+0x70/0xc0
[ 37.051924] driver_attach+0x28/0x3c
[ 37.055484] bus_add_driver+0x108/0x1f0
[ 37.059306] driver_register+0x7c/0x130
[ 37.063131] __platform_driver_register+0x2c/0x40
[ 37.067820] simple_pm_bus_driver_init+0x20/0x2c
[ 37.072424] do_one_initcall+0x54/0x1bc
[ 37.076249] kernel_init_freeable+0x210/0x294
[ 37.080591] kernel_init+0x28/0x130
[ 37.084068] ret_from_fork+0x10/0x20
[ 37.087688] simple-pm-bus bus@56220000: Dropping the link to 5d090000.gpio
[ 37.094501] device: 'platform:5d090000.gpio--platform:bus@56220000': device_unregister

So, before your patch, the devlinks were not dropped because there was
no driver to probe for the "simple-bus" compatible.

And I think this tells us why your hack patch didn't solve the problem
either.

>
> One more thing.
>
> So basically, your already upstream patch removes the devlinks for all the simple-bus
> nodes.
>
> By adding your hack patch, it also removes devlinks between subnodes of the simple-bus
> node.
>
> > > > I have some thoughts on how I could fix this, but I need to think
> > > > about a few cases.
> > >
> > > Hi Abel,
> > >
> > > Friendly reminder.
> > >
> >
> > Sorry for the late reply.
> >
> > > -Saravana