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

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Date:   Mon, 9 Nov 2020 12:42:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:     Aisheng Dong <aisheng.dong@....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

On Mon, Nov 09, 2020 at 11:18:56AM +0000, Sudip Mukherjee wrote:
> Hi Aisheng,
> 
> On Mon, Nov 9, 2020 at 10:57 AM Aisheng Dong <aisheng.dong@....com> 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.
> > > > > >
> 
> <snip>
> 
> > >
> > > 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?
> >
> > 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.
> 
> iiuc, you are waiting for "fsl,scu-pd" to be registered.
> I think you might be able to use bus_for_each_dev() to check if the
> device has registered with the bus or not. It will be on the bus only
> after bind was successful. The bus will be "platform_bus_type".

No, do not do that, again, no individual driver should ever have to do
that.  Think about what would be involved if _every_ driver started
doing this.

> But I am sure Greg can give you better suggestion than this. :)

device link :)

thanks,

greg k-h