Re: [PATCH] mtd: spi-nor: intel-spi: Do not try to make the SPI flash chip writable

From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Gutson <daniel@eclypsium.com>,
	Tudor Ambarus <tudor.ambarus@microchip.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Boris Brezillon <bbrezillon@kernel.org>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Alex Bazhaniuk <alex@eclypsium.com>,
	Richard Hughes <hughsient@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] mtd: spi-nor: intel-spi: Do not try to make the SPI flash chip writable
Date: Mon, 24 Aug 2020 12:44:48 +0300	[thread overview]
Message-ID: <20200824094448.GE1375436@lahna.fi.intel.com> (raw)
In-Reply-To: <CAK8P3a2ipcVLOzZ5jsDSmWkm=rsE7UQ8rgTU-o6me+vX+gVa9g@mail.gmail.com>

On Mon, Aug 24, 2020 at 11:31:40AM +0200, Arnd Bergmann wrote:
> On Mon, Aug 24, 2020 at 11:15 AM Mika Westerberg
> <mika.westerberg@linux.intel.com> wrote:
> > On Mon, Aug 24, 2020 at 11:08:33AM +0200, Arnd Bergmann wrote:
> > > On Mon, Aug 24, 2020 at 10:22 AM Mika Westerberg
> > > <mika.westerberg@linux.intel.com> wrote:
> > > > On Sat, Aug 22, 2020 at 06:06:03PM +0200, Arnd Bergmann wrote:
> > > > > On Wed, Aug 19, 2020 at 11:11 AM Mika Westerberg
> > > > >
> > > > > The mtd core just checks both the permissions on the device node (which
> > > > > default to 0600 without any special udev rules) and the MTD_WRITEABLE
> > > > > on the underlying device that is controlled by the module parameter
> > > > > in case of intel-spi{,-platform,-pci}.c.
> > > >
> > > > OK, thanks.
> > > >
> > > > Since we cannot really get rid of the module parameter (AFAIK there are
> > > > users for it), I still think we should just make the "writeable" to
> > > > apply to the PCI part as well. That should at least make it consistent,
> > > > and it also solves Daniel's case.
> > >
> > > Can you explain Daniel's case then? I still don't understand what he
> > > actually wants.
> > >
> > > As I keep repeating, the module parameter *does* apply to the pci
> > > driver front-end since it determines whether the driver will disallow
> > > writes to the mtd device without it. The only difference is that the pci
> > > driver will attempt to set the hardware bit without checking the
> > > module parameter first, while the platform driver does not. If the
> > > module parameter is not set however, the state of the hardware
> > > bit is never checked again.
> >
> > I think Daniel wants the PCI driver not to set the hardware bit by
> > default (same as the platform driver).
> 
> Sure, but *why*?

Because this is part of the platform firmware security check patch he is
also working on and, I guess making the flash chip writeable by default
is triggering some of the checks in that patch. Or something along those
lines ;-)