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From:   "Gangurde, Abhijit" <abhijit.gangurde@amd.com>
To:     Greg KH <gregkh@linuxfoundation.org>
CC:     "masahiroy@kernel.org" <masahiroy@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Simek, Michal" <michal.simek@amd.com>,
        "git (AMD-Xilinx)" <git@amd.com>,
        "Agarwal, Nikhil" <nikhil.agarwal@amd.com>,
        "Gupta, Nipun" <Nipun.Gupta@amd.com>
Subject: RE: [PATCH v2 1/4] cdx: Introduce lock to protect controller ops and
 controller list
Thread-Topic: [PATCH v2 1/4] cdx: Introduce lock to protect controller ops and
 controller list
Thread-Index: AQHZw6fpekS7+sewHkWP9KKMIHa4dK/TzKGAgAEccwCAADdNAIABuRcg
Date:   Wed, 2 Aug 2023 11:20:17 +0000
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References: <20230731120813.123247-1-abhijit.gangurde@amd.com>
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> > > From: Greg KH <gregkh@linuxfoundation.org>
> > > Sent: Monday, July 31, 2023 5:55 PM
> > > To: Gangurde, Abhijit <abhijit.gangurde@amd.com>
> > > Cc: masahiroy@kernel.org; linux-kernel@vger.kernel.org; Simek, Michal
> > > <michal.simek@amd.com>; git (AMD-Xilinx) <git@amd.com>; Agarwal,
> Nikhil
> > > <nikhil.agarwal@amd.com>; Gupta, Nipun <Nipun.Gupta@amd.com>
> > > Subject: Re: [PATCH v2 1/4] cdx: Introduce lock to protect controller=
 ops
> and
> > > controller list
> > >
> > > On Mon, Jul 31, 2023 at 05:38:10PM +0530, Abhijit Gangurde wrote:
> > > > Add a mutex lock to prevent race between controller ops initiated b=
y
> > > > the bus subsystem and the controller registration/unregistration.
> > > >
> > > > Signed-off-by: Abhijit Gangurde <abhijit.gangurde@amd.com>
> > > > ---
> > > >  drivers/cdx/cdx.c | 14 ++++++++++++++
> > > >  1 file changed, 14 insertions(+)
> > > >
> > > > diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
> > > > index d2cad4c670a0..66797c8fe400 100644
> > > > --- a/drivers/cdx/cdx.c
> > > > +++ b/drivers/cdx/cdx.c
> > > > @@ -72,6 +72,8 @@
> > > >
> > > >  /* CDX controllers registered with the CDX bus */
> > > >  static DEFINE_XARRAY_ALLOC(cdx_controllers);
> > > > +/* Lock to protect controller ops and controller list */
> > > > +static DEFINE_MUTEX(cdx_controller_lock);
> > >
> > > Wait, why do you have a local list and not just rely on the list the
> > > driver core has for you already?  Isn't this a duplicate list where y=
ou
> > > have objects on two different lists with a lifespan controlled only b=
y
> > > one of them?
> >
> > cdx_controllers list is holding just the controllers registered on the =
cdx bus
> system.
>=20
> Which are devices on the bus, so why do you need a separate list?
>=20
> > CDX devices are still maintained by driver core list. Controller list i=
s used by
> rescan
> > which triggers rescan on all the controllers.
>=20
> Again, why a separate list?  The driver core already tracks these,
> right?

As of now, cdx controllers are platform devices and maintained on cdx_contr=
ollers list.
CDX controller devices are not added on cdx bus. IIUC, you mean to use driv=
er core
list to find out different cdx controllers, in that case cdx bus would need=
 to scan=20
platform bus and access the private data of platform device to get a cdx_co=
ntroller ops.
IMHO, that would not be a right approach.

Or as an alternative cdx controller could be added on cdx bus as well. And =
we can then
get these controllers from driver core list.

Thanks,
Abhijit