Re: [RFC PATCH v2] PCI: Only enable IO window if supported

[Bjorn Helgaas <bhelgaas@google.com>]

On Tue, Jul 07, 2015 at 11:11:20AM -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 child bus 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 bus or its parent does not support
> I/O in the first place.
> 
> To avoid this message, check if a bus supports I/O before trying to
> enable it. Also check if the root bus has an IO window assigned;
> if not, it does not make sense to try to assign one to any of its
> child busses.
> 
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Applied to pci/resource for v4.3, thanks!

> ---
> v2: Use a new bus flag to indicate if IO is supported on a bus or not.
>     Using IORESOURCE_DISABLED in resource flags turned out to be futile,
>     since the term "!res->flags" is widely used to detect if a resource
>     window is enabled or not, and setting IORESOURCE_DISABLED would
>     affect all this code.
> 
> This patch depends on 'PCI: move pci_read_bridge_bases to the generic
> PCI layer' by Lorenzo Pieralisi; without it, pci_read_bridge_io()
> is not always called.
> 
> With this version of the patch, pci_bridge_check_ranges() still sets
> IORESOURCE_IO. Moving this into pci_read_bridge_io() had undesirable
> side effects and resulted in missing IO window assignments on one of
> the x86 platforms I tested with. I'll have to explore this further.
> 
>  drivers/pci/probe.c     | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/pci/setup-bus.c |  9 +--------
>  include/linux/pci.h     |  1 +
>  3 files changed, 48 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index cefd636681b6..b21cba7aeb79 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -332,6 +332,35 @@ static void pci_read_bases(struct pci_dev *dev, unsigned int howmany, int rom)
>  	}
>  }
>  
> +static bool pci_bus_supports_io(struct pci_bus *bus)
> +{
> +	struct pci_dev *dev = bus->self;
> +	u16 io;
> +
> +	pci_read_config_word(dev, PCI_IO_BASE, &io);
> +	if (!io) {
> +		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);
> +	}
> +	return !!io;
> +}
> +
> +static bool pci_root_has_io_resource(struct pci_bus *bus)
> +{
> +	struct resource *res;
> +	int i;
> +
> +	while (bus->parent)
> +		bus = bus->parent;
> +
> +	 pci_bus_for_each_resource(bus, res, i) {
> +		if (res && (res->flags & IORESOURCE_IO))
> +			return true;
> +	 }
> +	 return false;
> +}
> +
>  static void pci_read_bridge_io(struct pci_bus *child)
>  {
>  	struct pci_dev *dev = child->self;
> @@ -340,6 +369,23 @@ static void pci_read_bridge_io(struct pci_bus *child)
>  	struct pci_bus_region region;
>  	struct resource *res;
>  
> +	if (child->bus_flags & PCI_BUS_FLAGS_NO_IO)
> +		return;
> +
> +	if (!pci_bus_supports_io(child)) {
> +		dev_printk(KERN_DEBUG, &dev->dev,
> +			   "  bus does not support IO\n");
> +		child->bus_flags |= PCI_BUS_FLAGS_NO_IO;
> +		return;
> +	}
> +
> +	if (!pci_root_has_io_resource(child)) {
> +		dev_printk(KERN_DEBUG, &dev->dev,
> +			   "  no IO window on root bus\n");
> +		child->bus_flags |= PCI_BUS_FLAGS_NO_IO;
> +		return;
> +	}
> +
>  	io_mask = PCI_IO_RANGE_MASK;
>  	io_granularity = 0x1000;
>  	if (dev->io_window_1k) {
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 508cc56130e3..c8c7eecadbfe 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -744,7 +744,6 @@ 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;
> @@ -752,13 +751,7 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
>  	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 (!(bus->bus_flags & PCI_BUS_FLAGS_NO_IO))
>  		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 8a0321a8fb59..b910ed04aa0b 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -191,6 +191,7 @@ typedef unsigned short __bitwise pci_bus_flags_t;
>  enum pci_bus_flags {
>  	PCI_BUS_FLAGS_NO_MSI   = (__force pci_bus_flags_t) 1,
>  	PCI_BUS_FLAGS_NO_MMRBC = (__force pci_bus_flags_t) 2,
> +	PCI_BUS_FLAGS_NO_IO    = (__force pci_bus_flags_t) 4,
>  };
>  
>  /* These values come from the PCI Express Spec */
> -- 
> 2.1.0
>