linux-kernel - Re: [PATCH] base: soc: Export soc_device_to

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Message-ID: <20190919215300.GC1418@minitux>
Date:   Thu, 19 Sep 2019 14:53:00 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Murali Nalajala <mnalajal@...eaurora.org>, rafael@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] base: soc: Export soc_device_to_device API

On Thu 19 Sep 14:32 PDT 2019, Greg KH wrote:

> On Thu, Sep 19, 2019 at 02:13:44PM -0700, Murali Nalajala wrote:
> > If the soc drivers want to add custom sysfs entries it needs to
> > access "dev" field in "struct soc_device". This can be achieved
> > by "soc_device_to_device" API. Soc drivers which are built as a
> > module they need above API to be exported. Otherwise one can
> > observe compilation issues.
> > 
> > Signed-off-by: Murali Nalajala <mnalajal@...eaurora.org>
> > ---
> >  drivers/base/soc.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/base/soc.c b/drivers/base/soc.c
> > index 7c0c5ca..4ad52f6 100644
> > --- a/drivers/base/soc.c
> > +++ b/drivers/base/soc.c
> > @@ -41,6 +41,7 @@ struct device *soc_device_to_device(struct soc_device *soc_dev)
> >  {
> >  	return &soc_dev->dev;
> >  }
> > +EXPORT_SYMBOL_GPL(soc_device_to_device);
> >  
> >  static umode_t soc_attribute_mode(struct kobject *kobj,
> >  				struct attribute *attr,
> 
> What in-kernel driver needs this?
> 

Half of the drivers interacting with the soc driver calls this API,
several of these I see no reason for being builtin (e.g.
ux500 andversatile). So I think this patch makes sense to allow us to
build these as modules.

> Is linux-next breaking without this?
> 

No, we postponed the addition of any sysfs attributes in the Qualcomm
socinfo driver.

> We don't export things unless we have a user of the export.
> 
> Also, adding "custom" sysfs attributes is almost always not the correct
> thing to do at all.  The driver should be doing it, by setting up the
> attribute group properly so that the driver core can do it automatically
> for it.
> 
> No driver should be doing individual add/remove of sysfs files.  If it
> does so, it is almost guaranteed to be doing it incorrectly and racing
> userspace.
> 

The problem here is that the attributes are expected to be attached to
the soc driver, which is separate from the platform-specific drivers. So
there's no way to do platform specific attributes the right way.

> And yes, there's loads of in-kernel examples of doing this wrong, I've
> been working on fixing that up, look at the patches now in Linus's tree
> for platform and USB drivers that do this as examples of how to do it
> right.
> 

Agreed, this patch should not be used as an approval for any crazy
attributes; but it's necessary in order to extend the soc device's
attributes, per the current design.

So:

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn