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    SubjectRe: [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@google.com> wrote:
    >
    > On Wed, Nov 10, 2021 at 4:16 AM Abel Vesa <abelvesa@kernel.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@google.com>
    > > > Tested-by: Saravana Kannan <saravanak@google.com>
    > > > Tested-by: Ulf Hansson <ulf.hansson@linaro.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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