linux-kernel - RE: [PATCH 3/3] crypto: inside-secure

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Message-ID: <MN2PR20MB29736FBE530B603C71F99AD6CA6D0@MN2PR20MB2973.namprd20.prod.outlook.com>
Date:   Thu, 17 Oct 2019 14:14:03 +0000
From:   Pascal Van Leeuwen <pvanleeuwen@...imatrix.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Antoine Tenart <antoine.tenart@...tlin.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Pascal van Leeuwen <pascalvanl@...il.com>,
        Kelsey Skunberg <skunberg.kelsey@...il.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [PATCH 3/3] crypto: inside-secure - Remove #ifdef checks

> -----Original Message-----
> From: Arnd Bergmann <arnd@...db.de>
> Sent: Thursday, October 17, 2019 3:48 PM
> To: Pascal Van Leeuwen <pvanleeuwen@...imatrix.com>
> Cc: Antoine Tenart <antoine.tenart@...tlin.com>; Herbert Xu <herbert@...dor.apana.org.au>;
> David S. Miller <davem@...emloft.net>; Bjorn Helgaas <bhelgaas@...gle.com>; Pascal van Leeuwen
> <pascalvanl@...il.com>; Kelsey Skunberg <skunberg.kelsey@...il.com>; linux-
> crypto@...r.kernel.org; linux-kernel@...r.kernel.org; linux-pci@...r.kernel.org
> Subject: Re: [PATCH 3/3] crypto: inside-secure - Remove #ifdef checks
> 
> On Thu, Oct 17, 2019 at 3:26 PM Pascal Van Leeuwen
> <pvanleeuwen@...imatrix.com> wrote:
> 
> > >       /* Register PCI driver */
> > > -     pcireg_rc = pci_register_driver(&safexcel_pci_driver);
> > > -#endif
> > > +     ret = pci_register_driver(&safexcel_pci_driver);
> > >
> > > -#if IS_ENABLED(CONFIG_OF)
> > >       /* Register platform driver */
> > > -     ofreg_rc = platform_driver_register(&crypto_safexcel);
> > > - #if IS_ENABLED(CONFIG_PCI)
> > > -     /* Return success if either PCI or OF registered OK */
> > > -     return pcireg_rc ? ofreg_rc : 0;
> > > - #else
> > > -     return ofreg_rc;
> > > - #endif
> > > -#else
> > > - #if IS_ENABLED(CONFIG_PCI)
> > > -     return pcireg_rc;
> > > - #else
> > > -     return -EINVAL;
> > > - #endif
> > > -#endif
> > > +     if (IS_ENABLED(CONFIG_OF) && !ret) {
> > >
> > Hmm ... this would make it skip the OF registration if the PCIE
> > registration failed. Note that the typical embedded  system will
> > have a PCIE subsystem (e.g. Marvell A7K/A8K does) but will have
> > the EIP embedded on the SoC as an OF device.
> >
> > So the question is: is it possible somehow that PCIE registration
> > fails while OF registration does pass? Because in that case, this
> > code would be wrong ...
> 
> I don't see how it would fail. When CONFIG_PCI is disabled,
> pci_register_driver() does nothing, and the pci_driver as well
> as everything referenced from it will be silently dropped from
> the object file.
> If CONFIG_PCI is enabled, then the driver will be registered
> to the PCI subsystem, waiting for a device to show up, but
> the driver registration does not care about whether there is
> such a device.
> 
I know it does not care about the device being present or not.
I was just worried some issue with the PCIE subsystem would propagate
to (unrelated) OF device use this way. But I have no idea on the exact
ways PCIE registration may fail. If it is because of lack of memory,
I assume that subsequent OF device registration would fail as well.
So maybe I'm worried about an issue that doesn't really exist.

> > Other than that, I don't care much how this code is implemented
> > as long as it works for both my use cases, being an OF embedded
> > device (on a SoC _with_ or _without_ PCIE support) and a device
> > on a PCIE board in a PCI (which has both PCIE and OF support).
> 
> Yes, that should be fine. There are a lot of drivers that support
> multiple bus interfaces, and this is the normal way to handle them.
> 
Ok, if this is the "normal way to handle this" and a lot of other
drivers do it the same way, then I'm OK with that ...
I already verified it works correctly for my specific use cases.

Thanks.

>     Arnd

Regards,
Pascal van Leeuwen
Silicon IP Architect, Multi-Protocol Engines @ Verimatrix
www.insidesecure.com