linux-kernel - Re: [PATCH] pciehp: Add pciehp

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Date:	Wed, 20 Mar 2013 17:39:45 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Oliver Neukum <oneukum@...e.de>, Michal Marek <mmarek@...e.cz>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pciehp: Add pciehp_surprise module option

At Wed, 20 Mar 2013 09:33:18 -0700,
Randy Dunlap wrote:
> 
> On 03/20/13 07:02, Takashi Iwai 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.
> > 
> > This patch adds a new module option, pciehp_surprise, to pciehp as a
> > workaround.  When pciehp_surprise=1 is given, pciehp handles the
> > presence change as the device on/off as if PCI_EXP_SLTCAP_HPS is set.
> > Unless it's set explicitly, there is no impact on the existing
> > behavior.
> > 
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > ---
> >  drivers/pci/hotplug/pciehp.h      | 3 ++-
> >  drivers/pci/hotplug/pciehp_core.c | 3 +++
> >  2 files changed, 5 insertions(+), 1 deletion(-)
> > 
> 
> > diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
> > index 7d72c5e..c3a574e 100644
> > --- a/drivers/pci/hotplug/pciehp_core.c
> > +++ b/drivers/pci/hotplug/pciehp_core.c
> > @@ -55,10 +56,12 @@ module_param(pciehp_debug, bool, 0644);
> >  module_param(pciehp_poll_mode, bool, 0644);
> >  module_param(pciehp_poll_time, int, 0644);
> >  module_param(pciehp_force, bool, 0644);
> > +module_param(pciehp_surprise, bool, 0644);
> >  MODULE_PARM_DESC(pciehp_debug, "Debugging mode enabled or not");
> >  MODULE_PARM_DESC(pciehp_poll_mode, "Using polling mechanism for hot-plug events or not");
> >  MODULE_PARM_DESC(pciehp_poll_time, "Polling mechanism frequency, in seconds");
> >  MODULE_PARM_DESC(pciehp_force, "Force pciehp, even if OSHP is missing");
> > +MODULE_PARM_DESC(pciehp_surprise, "Force to set hotplug-surprise capability");
> 
> 
> It appears that all of the pciehp options need to be documented,
> preferably in Documentation/kernel-parameters.txt .

Yeah, makes sense.

Off-topic: it would have been nicer if pciehp_ prefix was removed at
the first place, too.  But it's too late and we need to live with it.


Takashi
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