linux-kernel - Re: [PATCH] SPI LPC information kernel module

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Message-ID: <CAK8P3a3rkiBMB55HJGi8T4Nw4gUrG2M=BAq+w=WMbS8DzwnPqw@mail.gmail.com>
Date:   Mon, 6 Jul 2020 12:22:17 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Daniel Gutson <daniel@...ypsium.com>
Cc:     Derek Kiernan <derek.kiernan@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Richard Hughes <hughsient@...il.com>,
        Alex Bazhaniuk <alex@...ypsium.com>,
        linux-pci <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] SPI LPC information kernel module

On Fri, Jul 3, 2020 at 10:43 PM Daniel Gutson <daniel@...ypsium.com> wrote:

> After analyzing the intel-spi driver, I came up to these observations that led me conclude that it is not what I need to use:
>
> * Some SPI Controllers have 0xFFFF as their VID DID bytes in the PCI config space. This causes that the PCI devices enumeration doesn't include them,
> and thus a PCI device driver won't be probed even despite listing the DID that the datasheet specifies. I effectively confirmed this by doing a PCI device driver and
> trying the intel-spi in systems with this characteristic. In short, the intel-spi driver doesn't work with these systems.

Maybe this part can be handled with a fixup in drivers/pci that
changes the effective
PCI device ID on the systems that do need to access the device.

Adding the PCI mailing list for other ideas. Basically it sounds like
the BIOS has
intentionally configured the SPI-NOR device to be hidden from PCI probing to
prevent operating systems from accessing it, but you want to ignore that and
access it anyway, correct?

      Arnd