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SubjectRe: [PATCH] PCI: Probe bridge window attributes once at enumeration-time
On Tue, Jan 22, 2019 at 01:02:54PM -0600, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
>
> pci_bridge_check_ranges() determines whether a bridge supports the optional
> I/O and prefetchable memory windows and sets the flag bits in the bridge
> resources. This *could* be done once during enumeration except that the
> resource allocation code completely clears the flag bits, e.g., in the
> pci_assign_unassigned_bridge_resources() path.
>
> The problem with pci_bridge_check_ranges() in the resource allocation path
> is that we may allocate resources after devices have been claimed by
> drivers, and pci_bridge_check_ranges() *changes* the window registers to
> determine whether they're writable. This may break concurrent accesses to
> devices behind the bridge.
>
> Add a new pci_read_bridge_windows() to determine whether a bridge supports
> the optional windows, call it once during enumeration, remember the
> results, and change pci_bridge_check_ranges() so it doesn't touch the
> bridge windows but sets the flag bits based on those remembered results.
>
> Link: https://lore.kernel.org/linux-pci/1506151482-113560-1-git-send-email-wangzhou1@hisilicon.com
> Link: https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg02082.html
> Reported-by: xuyandong <xuyandong2@huawei.com>
> Tested-by: xuyandong <xuyandong2@huawei.com>
> Cc: Sagi Grimberg <sagi@grimberg.me>
> Cc: Ofer Hayut <ofer@lightbitslabs.com>
> Cc: Roy Shterman <roys@lightbitslabs.com>
> Cc: Keith Busch <keith.busch@intel.com>
> Cc: Zhou Wang <wangzhou1@hisilicon.com>

Applied to pci/enumeration for v5.1.

This is fairly simple in concept, but doesn't meet the letter of the
restrictions in Documentation/process/stable-kernel-rules.rst, so I
didn't tag it for stable.

Is there a compelling argument to mark it for stable?

> ---
> drivers/pci/probe.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++
> drivers/pci/setup-bus.c | 45 ++++-------------------------------------
> include/linux/pci.h | 3 +++
> 3 files changed, 59 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 257b9f6f2ebb..2ef8b954c65a 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -348,6 +348,57 @@ static void pci_read_bases(struct pci_dev *dev, unsigned int howmany, int rom)
> }
> }
>
> +static void pci_read_bridge_windows(struct pci_dev *bridge)
> +{
> + u16 io;
> + u32 pmem, tmp;
> +
> + pci_read_config_word(bridge, PCI_IO_BASE, &io);
> + if (!io) {
> + 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)
> + bridge->io_window = 1;
> +
> + /*
> + * DECchip 21050 pass 2 errata: the bridge may miss an address
> + * disconnect boundary by one PCI data phase. Workaround: do not
> + * use prefetching on this device.
> + */
> + if (bridge->vendor == PCI_VENDOR_ID_DEC && bridge->device == 0x0001)
> + return;
> +
> + pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
> + if (!pmem) {
> + pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE,
> + 0xffe0fff0);
> + pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
> + pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE, 0x0);
> + }
> + if (!pmem)
> + return;
> +
> + bridge->pref_window = 1;
> +
> + if ((pmem & PCI_PREF_RANGE_TYPE_MASK) == PCI_PREF_RANGE_TYPE_64) {
> +
> + /*
> + * Bridge claims to have a 64-bit prefetchable memory
> + * window; verify that the upper bits are actually
> + * writable.
> + */
> + pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32, &pmem);
> + pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> + 0xffffffff);
> + pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32, &tmp);
> + pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32, pmem);
> + if (tmp)
> + bridge->pref_64_window = 1;
> + }
> +}
> +
> static void pci_read_bridge_io(struct pci_bus *child)
> {
> struct pci_dev *dev = child->self;
> @@ -1739,6 +1790,7 @@ int pci_setup_device(struct pci_dev *dev)
> pci_read_irq(dev);
> dev->transparent = ((dev->class & 0xff) == 1);
> pci_read_bases(dev, 2, PCI_ROM_ADDRESS1);
> + pci_read_bridge_windows(dev);
> set_pcie_hotplug_bridge(dev);
> pos = pci_find_capability(dev, PCI_CAP_ID_SSVID);
> if (pos) {
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index ed960436df5e..1941bb0a6c13 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -735,58 +735,21 @@ int pci_claim_bridge_resource(struct pci_dev *bridge, int i)
> base/limit registers must be read-only and read as 0. */
> static void pci_bridge_check_ranges(struct pci_bus *bus)
> {
> - u16 io;
> - u32 pmem;
> struct pci_dev *bridge = bus->self;
> - struct resource *b_res;
> + struct resource *b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];
>
> - b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];
> b_res[1].flags |= IORESOURCE_MEM;
>
> - pci_read_config_word(bridge, PCI_IO_BASE, &io);
> - if (!io) {
> - 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 (bridge->io_window)
> b_res[0].flags |= IORESOURCE_IO;
>
> - /* DECchip 21050 pass 2 errata: the bridge may miss an address
> - disconnect boundary by one PCI data phase.
> - Workaround: do not use prefetching on this device. */
> - if (bridge->vendor == PCI_VENDOR_ID_DEC && bridge->device == 0x0001)
> - return;
> -
> - pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
> - if (!pmem) {
> - pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE,
> - 0xffe0fff0);
> - pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
> - pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE, 0x0);
> - }
> - if (pmem) {
> + if (bridge->pref_window) {
> b_res[2].flags |= IORESOURCE_MEM | IORESOURCE_PREFETCH;
> - if ((pmem & PCI_PREF_RANGE_TYPE_MASK) ==
> - PCI_PREF_RANGE_TYPE_64) {
> + if (bridge->pref_64_window) {
> b_res[2].flags |= IORESOURCE_MEM_64;
> b_res[2].flags |= PCI_PREF_RANGE_TYPE_64;
> }
> }
> -
> - /* double check if bridge does support 64 bit pref */
> - if (b_res[2].flags & IORESOURCE_MEM_64) {
> - u32 mem_base_hi, tmp;
> - pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> - &mem_base_hi);
> - pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> - 0xffffffff);
> - pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32, &tmp);
> - if (!tmp)
> - b_res[2].flags &= ~IORESOURCE_MEM_64;
> - pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
> - mem_base_hi);
> - }
> }
>
> /* Helper function for sizing routines: find first available
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 65f1d8c2f082..40b327b814aa 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -373,6 +373,9 @@ struct pci_dev {
> bool match_driver; /* Skip attaching driver */
>
> unsigned int transparent:1; /* Subtractive decode bridge */
> + unsigned int io_window:1; /* Bridge has I/O window */
> + unsigned int pref_window:1; /* Bridge has pref mem window */
> + unsigned int pref_64_window:1; /* Pref mem window is 64-bit */
> unsigned int multifunction:1; /* Multi-function device */
>
> unsigned int is_busmaster:1; /* Is busmaster */
>

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