linux-kernel - Re: [RFC PATCH v2 6/6] driver core: add compatible string in sysfs for platform devices

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Date:   Wed, 17 Aug 2022 09:04:18 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Nipun Gupta <nipun.gupta@....com>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, rafael@...nel.org,
        eric.auger@...hat.com, alex.williamson@...hat.com,
        cohuck@...hat.com, puneet.gupta@....com,
        song.bao.hua@...ilicon.com, mchehab+huawei@...nel.org,
        maz@...nel.org, f.fainelli@...il.com, jeffrey.l.hugo@...il.com,
        Michael.Srba@...nam.cz, mani@...nel.org, yishaih@...dia.com,
        jgg@...pe.ca, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, kvm@...r.kernel.org, okaya@...nel.org,
        harpreet.anand@....com, nikhil.agarwal@....com,
        michal.simek@....com, git@....com
Subject: Re: [RFC PATCH v2 6/6] driver core: add compatible string in sysfs
 for platform devices

On Wed, Aug 17, 2022 at 8:31 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Aug 17, 2022 at 08:35:42PM +0530, Nipun Gupta wrote:
> > This change adds compatible string for the platform based
> > devices.
>
> What exactly is a "compatible string"?

Didn't read the rest of the patches in the series yet, but Nack to
this. This info is already available under:

<device folder>/of_node/compatible for any device in any (or at least
most) bus that was created from an of_node.

Unless compatible is now also in ACPI. In which case, it's probably be
better to have an of_node like symlink.


-Saravana

>
> >
> > Signed-off-by: Nipun Gupta <nipun.gupta@....com>
> > ---
> >  Documentation/ABI/testing/sysfs-bus-platform |  8 +++++++
> >  drivers/base/platform.c                      | 23 ++++++++++++++++++++
> >  2 files changed, 31 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform
> > index c4dfe7355c2d..d95ff83d768c 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-platform
> > +++ b/Documentation/ABI/testing/sysfs-bus-platform
> > @@ -54,3 +54,11 @@ Description:
> >               Other platform devices use, instead:
> >
> >                       - platform:`driver name`
> > +
> > +What:                /sys/bus/platform/devices/.../compatible
> > +Date:                August 2022
> > +Contact:     Nipun Gupta <nipun.gupta@....com>
> > +Description:
> > +             compatible string associated with the device. This is
> > +             a read only and is visible if the device have "compatible"
> > +             property associated with it.
>
> Where is it defined what a compatible property is?
>
> > diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> > index 51bb2289865c..94c33efaa9b8 100644
> > --- a/drivers/base/platform.c
> > +++ b/drivers/base/platform.c
> > @@ -1289,10 +1289,25 @@ static ssize_t driver_override_store(struct device *dev,
> >  }
> >  static DEVICE_ATTR_RW(driver_override);
> >
> > +static ssize_t compatible_show(struct device *dev, struct device_attribute *attr,
> > +                           char *buf)
> > +{
> > +     const char *compat;
> > +     int ret;
> > +
> > +     ret = device_property_read_string(dev, "compatible", &compat);
> > +     if (ret != 0)
> > +             return 0;
>
> Shouldn't you return an error here?
>
> thanks,
>
> greg k-h