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Date:   Mon, 9 Nov 2020 13:05:12 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Aisheng Dong <aisheng.dong@nxp.com>
Cc:     Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>
Subject: Re: [PATCH RESEND] driver core: export device_is_bound() to fix
 build failure
Message-ID: <20201109120512.GB1832201@kroah.com>
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On Mon, Nov 09, 2020 at 11:55:46AM +0000, Aisheng Dong wrote:
> > From: Greg Kroah-Hartman <gregkh@linuxfoundation.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@linuxfoundation.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@linuxfoundation.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@gmail.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?

Also, how do you really know you even have a valid pointer to that other
device structure?  How are you getting access to that?

thanks,

greg k-h