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Date: Tue, 2 Jun 2015 15:55:10 +0100
From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Guenter Roeck <linux@...ck-us.net>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
Will Deacon <Will.Deacon@....com>
Subject: Re: [PATCH] PCI: Only enable IO window if supported
Bjorn, Guenter,
On Wed, May 27, 2015 at 10:04:47PM +0100, Bjorn Helgaas wrote:
> [+cc Lorenzo, Suravee, Will]
>
> I cc'd Lorenzo, Suravee, and Will because Lorenzo is working on calling
> pci_read_bases() from the PCI core instead of from arch code, and there are
> likely some dependencies between these two things.
>
> On Fri, May 22, 2015 at 05:52:16PM -0700, Guenter Roeck wrote:
> > The PCI subsystem always assumes that I/O is supported on PCIe bridges
> > and tries to assign an I/O window to each port even if that is not
> > the case.
> >
> > This may result in messages such as
> >
> > pcieport 0000:02:00.0: res[7]=[io 0x1000-0x0fff]
> > get_res_add_size add_size 1000
> > pcieport 0000:02:00.0: BAR 7: no space for [io size 0x1000]
> > pcieport 0000:02:00.0: BAR 7: failed to assign [io size 0x1000]
> >
> > for each bridge port, even if a port or its parent does not support
> > I/O in the first place.
> >
> > To avoid this message, check if a port supports I/O before trying to
> > enable it. Also check if port's parent supports I/O, and only modify
> > a port's I/O resource size if both the port and its parent support I/O.
> >
> > If IO is disabled after the initial port scan, the IO base and size
> > registers are set to 0x00f0 to indicate that IO is disabled. A later
> > rescan interprets this as "IO supported" and enables the IO range,
> > even if the parent does not support IO. Handle this situation as well.
> >
> > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > ---
> > drivers/pci/probe.c | 14 ++++++++++++++
> > drivers/pci/setup-bus.c | 4 ++--
> > include/linux/pci.h | 9 +++++++++
> > 3 files changed, 25 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 6675a7a1b9fc..f4944ef45148 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -354,6 +354,20 @@ static void pci_read_bridge_io(struct pci_bus *child)
> > base = (io_base_lo & io_mask) << 8;
> > limit = (io_limit_lo & io_mask) << 8;
> >
> > + /* If necessary, check if the bridge supports an I/O aperture */
> > + if (!io_base_lo && !io_limit_lo) {
> > + u16 io;
> > +
> > + if (!pci_parent_supports_io(child))
> > + return;
> > +
> > + pci_write_config_word(dev, PCI_IO_BASE, 0xe0f0);
> > + pci_read_config_word(dev, PCI_IO_BASE, &io);
> > + pci_write_config_word(dev, PCI_IO_BASE, 0x0);
> > + if (!io)
> > + return;
> > + }
>
> I really like the idea of pushing this into pci_read_bridge_io().
>
> I wonder if we can do the same with pci_read_bridge_mmio_pref(), and
> somehow get rid of pci_bridge_check_ranges() altogether?
>
> I think I looked at doing that a while back, and it seems like there was
> some wrinkle, but I don't remember what it was.
While at it, do you think it is reasonable to also claim the bridge
windows (resources) in the respective pci_read_bridge_* calls ?
Is there a reason why we don't/can't do it ? I noticed that on
PROBE_ONLY systems on ARM/ARM64 at the moment we do not claim
the bridge apertures and this is not correct, see below:
[5.980127] pcieport 0000:00:02.1: can't enable device: BAR 8
[mem 0xbff00000 - 0xbfffffff] not claimed
[5.988056] pcieport: probe of 0000:00:02.1 failed with error -22
Thanks,
Lorenzo
> It does make sense that if the bridge supports an I/O aperture, but there's
> no possibility of I/O resources on the primary side, we should pretend the
> bridge has no I/O aperture. But I think it might be nice to emit a
> diagnostic about *why* we're ignoring it. Otherwise there's a little
> discrepancy between dmesg and lspci.
>
> > +
> > if ((io_base_lo & PCI_IO_RANGE_TYPE_MASK) == PCI_IO_RANGE_TYPE_32) {
> > u16 io_base_hi, io_limit_hi;
> >
> > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> > index 4fd0cacf7ca0..963b31a109a9 100644
> > --- a/drivers/pci/setup-bus.c
> > +++ b/drivers/pci/setup-bus.c
> > @@ -750,12 +750,12 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
> > b_res[1].flags |= IORESOURCE_MEM;
> >
> > pci_read_config_word(bridge, PCI_IO_BASE, &io);
> > - if (!io) {
> > + if (!io && pci_parent_supports_io(bus)) {
> > pci_write_config_word(bridge, PCI_IO_BASE, 0xe0f0);
> > pci_read_config_word(bridge, PCI_IO_BASE, &io);
> > pci_write_config_word(bridge, PCI_IO_BASE, 0x0);
> > }
> > - if (io)
> > + if (io && (io != 0x00f0 || pci_parent_supports_io(bus)))
>
> I *think* this 0x00f0 depends on what pci_setup_bridge_io() writes to
> PCI_IO_BASE when it disables an I/O aperture. Depending on that particular
> value here is sort of ugly and would need at least a comment if we can't
> figure out a better way to do it.
>
> But it would be ideal if we could get rid of pci_bridge_check_ranges()
> altogether and have the rule that we read bridge window characteristics
> (IORESOURCE_IO, IORESOURCE_MEM, IORESOURCE_PREFETCH, IORESOURCE_MEM_64)
> once when we enumerate the bridge. After that, the only changes would be
> to change res->start and res->end and update the hardware correspondingly.
>
> I'd like res->flags to reflect the capabilities of the hardware, not
> whether the window is currently enabled.
>
> > b_res[0].flags |= IORESOURCE_IO;
> >
> > /* DECchip 21050 pass 2 errata: the bridge may miss an address
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 353db8dc4c6e..f3de9e24aab1 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -489,6 +489,15 @@ static inline bool pci_is_root_bus(struct pci_bus *pbus)
> > return !(pbus->parent);
> > }
> >
> > +/*
> > + * Returns true if the parent bus supports an I/O aperture.
> > + */
> > +static inline bool pci_parent_supports_io(struct pci_bus *pbus)
> > +{
> > + return pci_is_root_bus(pbus) || pci_is_root_bus(pbus->parent) ||
> > + (pbus->parent->resource[0]->flags & IORESOURCE_IO);
>
> This is not obvious to me. There are host bridges that do not have I/O
> apertures, so I don't see what the pci_is_root_bus() tests have to do with
> this. The resource[0]->flags & IORESOURCE_IO part does make sense to me.
>
> I think at the root bus, we'd have to iterate through all the host bridge
> resources to figure out whether there are any I/O apertures.
>
> > +}
> > +
> > /**
> > * pci_is_bridge - check if the PCI device is a bridge
> > * @dev: PCI device
> > --
> > 2.1.0
> >
>
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