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

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Date:   Mon, 9 Nov 2020 11:32:28 +0000
From:   Aisheng Dong <aisheng.dong@....com>
To:     Sudip Mukherjee <sudipm.mukherjee@...il.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "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: Sudip Mukherjee <sudipm.mukherjee@...il.com>
> Sent: Monday, November 9, 2020 7:19 PM
> 
> 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".
> But I am sure Greg can give you better suggestion than this. :)
> 

Thanks for the suggestion. Seems like a working tricky method. :-)
For a possible easier way, I wonder if we can use dev_driver_string() which is already
exported in kernel.
Waiting for Greg's suggestions on which way to go.

Regards
Aisheng

> 
> --
> Regards
> Sudip