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From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Tue, 25 Feb 2020 23:51:05 -0500
To:     Trevor Jacobs <trevor_jacobs@aol.com>
Cc:     "Michael ." <keltoiboy@gmail.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Linux PCI <linux-pci@vger.kernel.org>,
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        Kris Cleveland <tridentperfusion@yahoo.com>,
        Jeff <bluerocksaddles@willitsonline.com>,
        Morgan Klym <moklym@gmail.com>,
        Philip Langdale <philipl@overt.org>,
        Pierre Ossman <pierre@ossman.eu>,
        Maxim Levitsky <maximlevitsky@gmail.com>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>
Subject: Re: PCI device function not being enumerated [Was: PCMCIA not
 working on Panasonic Toughbook CF-29]
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On Tue, Feb 25, 2020 at 09:12:48PM -0600, Trevor Jacobs wrote:
> That's correct, I tested a bunch of the old distros including slackware, 
> and 2.6.32 is where the problem began.
> 
> Also, the Panasonic Toughbook CF-29s effected that we tested are the 
> later marks, MK4 and MK5 for certain. The MK2 CF-29 worked just fine 
> because it has different hardware supporting the PCMCIA slots. I have 
> not tested a MK3 but suspect it would work ok as it also uses the older 
> hardware.
> 
> Thanks for your help guys!
> Trevor
> 

Right, the distros probably all enabled MMC_RICOH_MMC earlier than
upstream. Can you test a custom kernel based off your distro kernel but
just disabling that config option? That's probably the easiest fix
currently, even though not ideal. Perhaps there should be a command line
option to disable specific pci quirks to make this easier.

An ideal fix is I feel hard, given this quirk is based on undocumented
config registers -- it worked on Dell machines (that's where the
original authors seem to have gotten their info from), perhaps they had
only one Cardbus slot, but the code ends up disabling your second
Cardbus slot instead of disabling the MMC controller.