linux-kernel - RE: [PATCH RESEND] driver core: export device_is

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Date:   Mon, 9 Nov 2020 11:55:46 +0000
From:   Aisheng Dong <aisheng.dong@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>
Subject: RE: [PATCH RESEND] driver core: export device_is_bound() to fix build
 failure

> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Sent: Monday, November 9, 2020 7:41 PM
> 
> On Mon, Nov 09, 2020 at 10:57:05AM +0000, Aisheng Dong wrote:
> > Hi Greg,
> >
> > > From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > Sent: Monday, November 9, 2020 6:37 PM
> > > Subject: Re: [PATCH RESEND] driver core: export device_is_bound() to
> > > fix build failure
> > >
> > > On Mon, Nov 09, 2020 at 10:14:46AM +0000, Sudip Mukherjee wrote:
> > > > Hi Greg,
> > > >
> > > > On Sun, Nov 8, 2020 at 8:23 AM Greg Kroah-Hartman
> > > > <gregkh@...uxfoundation.org> wrote:
> > > > >
> > > > > On Sat, Nov 07, 2020 at 10:47:27PM +0000, Sudip Mukherjee wrote:
> > > > > > When CONFIG_MXC_CLK_SCU is configured as 'm' the build fails
> > > > > > as it is unable to find device_is_bound(). The error being:
> > > > > > ERROR: modpost: "device_is_bound" [drivers/clk/imx/clk-imx-scu.ko]
> > > > > >       undefined!
> > > > > >
> > > > > > Export the symbol so that the module finds it.
> > > > > >
> > > > > > Fixes: 77d8f3068c63 ("clk: imx: scu: add two cells binding
> > > > > > support")
> > > > > > Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>
> > > > > > ---
> > > > > >
> > > > > > resending with the Fixes: tag.
> > > > > >
> > > > > >  drivers/base/dd.c | 1 +
> > > > > >  1 file changed, 1 insertion(+)
> > > > > >
> > > > > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c index
> > > > > > 148e81969e04..a796a57e5efb 100644
> > > > > > --- a/drivers/base/dd.c
> > > > > > +++ b/drivers/base/dd.c
> > > > > > @@ -353,6 +353,7 @@ bool device_is_bound(struct device *dev)  {
> > > > > >       return dev->p &&
> > > > > > klist_node_attached(&dev->p->knode_driver);
> > > > > >  }
> > > > > > +EXPORT_SYMBOL(device_is_bound);
> > > > >
> > > > > EXPORT_SYMBOL_GPL() please, like all the other exports in this file.
> > > > >
> > > > > Also, wait, no, don't call this, are you sure you are calling it
> > > > > in a race-free way?  And what branch/tree is the above commit in?
> > > >
> > > > I have not checked fully but since it is being called from probe()
> > > > I assume the lock will be held at that time.
> > >
> > > probe() should never call this function as it makes no sense at all
> > > at that point in time.  The driver should be fixed.
> >
> > Would you suggest if any other API we can use to allow the driver to
> > know whether another device has been probed?
> 
> There is none, sorry, as that just opens up way too many problems.
> 
> > For imx scu driver in question, it has a special requirement that it
> > depends on scu power domain driver. However, there're a huge number
> > (200+) of power domains for each device clock, we can't define them all in DT
> for a single clock controller node.
> >
> > That's why we wanted to use device_is_bound() before to check if scu
> > power domain is ready or not to support defer probe.
> 
> Use the device link functionality for this type of thing, that is what it was created
> for.
> 

Thanks for the suggestion. I will check it how to use.
BTW, I wonder if dev_driver_string() could be an optional solution which seems a more
simple way?

Regards
Aisheng

> thanks,
> 
> greg k-h