From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 27 May 2015 19:23:32 -0700 From: Guenter Roeck To: Bjorn Helgaas Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Lorenzo Pieralisi , Suravee Suthikulpanit , Will Deacon Subject: Re: [PATCH] PCI: Only enable IO window if supported Message-ID: <20150528022332.GA23724@roeck-us.net> References: <1432342336-25832-1-git-send-email-linux@roeck-us.net> <20150527210447.GY32152@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20150527210447.GY32152@google.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: On Wed, May 27, 2015 at 04:04:47PM -0500, 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 > > --- > > 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? > Sure, I just figured I'd start with IO, and do the rest after I have a better idea if I am going into the right direction. > 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. > > 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. > Ok, makes sense. Would you want to see that message for every port ? Guess I can check how it looks like, to make sure that I don't end up getting a lot of noise again. > > + > > 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 Correct. I could have checked if io is disabled (limit < base), but at least for the time being I wanted the impact to be minimal. So far the code auto-enables IO if it was disabled (eg by the BIOS) but the bridge chip supports it. I only wanted to keep it disabled if it was likely that it was disabled by pci_setup_bridge_io(). Of course, if (io && pci_parent_supports_io(bus)) might just be sufficient. > 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. > Would be great - this should solve the above problem automatically. I was hesitant to do that, because I don't know if there would be side effects. I could take out the io handling from pci_bridge_check_ranges() and see what happens, but obviously my test coverage would be somewhat limited. > I'd like res->flags to reflect the capabilities of the hardware, not > whether the window is currently enabled. > Flag bits seem to be all taken. Could we use IORESOURCE_DISABLED for that purpose, or could that cause conflicts elsewhere ? > > 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. > More a matter of me not knowing what I need to do. resource[0] is NULL for the root bus, at least on the powerpc system I used for testing. > 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. > Can you give me a hint on how to do that, hopefully in a platform independent way ? Walk through bus->resources and search for an IO resource ? Or does resource[0] == NULL already indicate that there is no IO aperture ? Thanks, Guenter