linux-kernel - Re: [PATCH] pci: host: xgene: fix incorrectly returned address by map

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Message-ID: <20150306041243.GA20077@google.com>
Date:	Thu, 5 Mar 2015 22:12:43 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Feng Kan <fkan@....com>
Cc:	patches <patches@....com>, linux-pci@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Mark Salter <msalter@...hat.com>
Subject: Re: [PATCH] pci: host: xgene: fix incorrectly returned address by
 map_bus

On Thu, Mar 05, 2015 at 08:53:38AM -0800, Feng Kan wrote:
> Please take Mark's patch if you think it is better.
> 
> 
> 
> On Thu, Mar 5, 2015 at 8:38 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> > [+cc Mark]
> >
> > On Thu, Feb 26, 2015 at 06:21:51PM -0600, Bjorn Helgaas wrote:
> >> On Tue, Feb 17, 2015 at 03:14:00PM -0800, Feng Kan wrote:
> >> > The generic accessor functions for pci-xgene uses map_bus
> >> > call that returns the base address but did not add the additional
> >> > offset.
> >> >
> >> > Signed-off-by: Feng Kan <fkan@....com>
> >> > ---
> >> >  drivers/pci/host/pci-xgene.c | 4 ++--
> >> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >> >
> >> > diff --git a/drivers/pci/host/pci-xgene.c b/drivers/pci/host/pci-xgene.c
> >> > index aab5547..ee082c0 100644
> >> > --- a/drivers/pci/host/pci-xgene.c
> >> > +++ b/drivers/pci/host/pci-xgene.c
> >> > @@ -127,7 +127,7 @@ static bool xgene_pcie_hide_rc_bars(struct pci_bus *bus, int offset)
> >> >     return false;
> >> >  }
> >> >
> >> > -static int xgene_pcie_map_bus(struct pci_bus *bus, unsigned int devfn,
> >> > +static void __iomem *xgene_pcie_map_bus(struct pci_bus *bus, unsigned int devfn,
> >> >                           int offset)
> >> >  {
> >> >     struct xgene_pcie_port *port = bus->sysdata;
> >> > @@ -137,7 +137,7 @@ static int xgene_pcie_map_bus(struct pci_bus *bus, unsigned int devfn,
> >> >             return NULL;
> >> >
> >> >     xgene_pcie_set_rtdid_reg(bus, devfn);
> >> > -   return xgene_pcie_get_cfg_base(bus);
> >> > +   return xgene_pcie_get_cfg_base(bus) + offset;
> >>
> >> Where's the locking here?  ECAM doesn't need locking because the
> >> bus/dev/fn/offset is all encoded in the MMIO address.  But it looks
> >> like X-Gene doesn't work that way and bus/dev/fn is in the RTDID register.
> >>
> >> So it seems like X-Gene needs locking that not everybody needs.  Are you
> >> relying on higher-level locking somewhere?
> >
> > Ping, what's going on here?  I've gotten at least three patches for this
> > offset issue, so we need to get it resolved.
> >
> > If there's no locking problem, I can just apply this and we'll be finished.
> > Actually, I think Mark's patch is better, because it correctly returns NULL
> > (failure) if xgene_pcie_get_cfg_base() fails.  So please review and ack
> > that one or explain why this one is better.

Huh, I could swear I saw a failure path in xgene_pcie_get_cfg_base().  But
I don't see a way it can fail, so I don't think it matters which way we fix
this.

Bjorn
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