Date:	Wed, 10 Apr 2013 11:19:48 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Oliver Neukum <oneukum@...e.de>, Michal Marek <mmarek@...e.cz>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	Matthew Garrett <matthew.garrett@...ula.com>
Subject: Re: [PATCH] pciehp: Add pciehp_surprise module option

On Wed, Apr 10, 2013 at 10:34 AM, Takashi Iwai <tiwai@...e.de> wrote:
> Hi Bjorn,
>
> sorry for the late follow up as I was on vacation and has been busy
> for other tasks.  Since this topic went to nirvana, I try to whip
> again...
>
> At Mon, 25 Mar 2013 10:58:40 -0600,
> Bjorn Helgaas wrote:
>>
>> On Wed, Mar 20, 2013 at 8:02 AM, Takashi Iwai <tiwai@...e.de> wrote:
>> > We encountered a problem that on some HP machines the Realtek PCI-e
>> > card reader device appears only when you inserted a card before the
>> > cold boot.  While debugging, it turned out that the device is actually
>> > handled via PCI-e hotplug in some level.  The device sends a presence
>> > change notification, and pciehp receives it, but it's ignored because
>> > of lack of the hotplug surprise (PCI_EXP_SLTCAP_HPS) capability bit.
>> > Once when this check passes, everything starts working -- the device
>> > appears upon plugging the card properly.
>> >
>> > There are a few other bug reports indicating the similar problems
>> > (e.g. on recent Dell laptops), and I guess the culprit is same.
>>
>> Can you point us at these bug reports, e.g., with URLs?  Hopefully
>> they will contain complete dmesg logs and "lspci -vv" outputs so we
>> can debug this a bit more.
>
> The machine isn't in market yet, so we cannot expose all things, but I
> attach the lspci snippet of the relevant parts, pci-e ports and the
> card reader, at least.  If you need anything else, let me know.
>
> As Oliver and Michal already replied, Windows (both 7/8) identifies
> the device without modification.  This implies that Windows handles
> the hotplug no matter whether the surprise bit is set or not, either
> globally or device-specifically.  But, since this is pretty new
> hardware, we highly doubt it's done in a white-list basis.
>
>> I'm strongly opposed to adding a module option to work around this
>> issue because the user experience is unacceptable.  We can't expect
>> users to debug the problem and discover the option.
>>
>> I'm also opposed to a DMI quirk system because I think it's very
>> likely that this device works correctly under Windows, and I doubt
>> very much that Windows has to include the equivalent of DMI quirks.
>> So we should, at least in principle, be able to figure out how to make
>> it work, too.
>
> In order to get things a bit straight, let me list up the things we
> found again:
>
> - The Realtek card reader devices doesn't appear in lspci at the
>   fresh boot in multiple kernel versions from 3.0 to 3.9.
>
> - Once when the card is inserted, it issues the hotplug IRQ event.
>
> - pciehp receives and handles the event but it doesn't add/remove the
>   device actually because the corresponding controller has no surprise
>   bit.
>
>   When forcibly enabling the hotplug device addition by my patch, it
>   starts working.  The device is added at card insert.  The removal
>   doesn't trigger on our system, but the event itself seems
>   generated.
>
> - The surprise bit can't be changed as it's supposed to be read-only
>   register bits.  Thus no PCI quirk seems possible, and it has to be
>   fixed in pciehp.
>
> - Another way to detect the PCI card reader device is to perform
>      echo 1 > /sys/bus/pci/rescan
>   with a memory card inserted.  It doesn't work without the card,
>   and it is less sophisticated than pciehp, of course.
>
> Right now, we applied a patch for pciehp to ignore the surprise bit
> per basis of DMI string match.  This works, but doesn't scale; if the
> same problem happens on a similar model, the driver must be compiled
> again.  A module option would be really convenient for that, although
> I understand your concern, too.
>
> Of course, an alternative (and more radical) solution is to remove the
> surprise bit check completely from pciehp, as Matthew suggested in the
> thread.  What risk would it bring?

I think we need to ignore the surprise bit as Matthew suggested.

Alex raised an issue with this (secondary bus reset causes a device
remove followed by device add), so we'd have to work through that
somehow.  I think doing the remove/add would actually be more correct
because we would be doing the whole device initialization after the
reset.  We currently save/restore some device state around the reset,
but that's a piecemeal approach that is certain to miss internal
hidden state.  But I don't know how to deal with the KVM implications
of remove/add.

Bjorn
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