Date:   Mon, 15 Nov 2021 12:17:46 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Abel Vesa <abelvesa@...nel.org>
Cc:     Russell King <linux@...linux.org.uk>,
        Neil Armstrong <narmstrong@...libre.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Damien Le Moal <damien.lemoal@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, kernel-team@...roid.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-oxnas@...ups.io, linux-renesas-soc@...r.kernel.org,
        linux-omap@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 1/2] drivers: bus: simple-pm-bus: Add support for
 probing simple bus only devices

On Wed, Nov 10, 2021 at 12:24 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> On Wed, Nov 10, 2021 at 4:16 AM Abel Vesa <abelvesa@...nel.org> 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@mail.gmail.com/
> > > Fixes: c442a0d18744 ("driver core: Set fw_devlink to "permissive" behavior by default")
> > > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > > Tested-by: Saravana Kannan <saravanak@...gle.com>
> > > Tested-by: Ulf Hansson <ulf.hansson@...aro.org>
> > > ---
> > >  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).
>
> Also, can you try this hack patch to see if it helps your case?
> https://lore.kernel.org/lkml/CAGETcx9U130Oq-umrvXME4JhEpO0Wadoki3kNxx=0-YvTR6PtQ@mail.gmail.com/
>
> I have some thoughts on how I could fix this, but I need to think
> about a few cases.

Hi Abel,

Friendly reminder.

-Saravana

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