Re: [PATCH] PCI: Probe bridge window attributes once at enumeration-time

[Bjorn Helgaas]

On Tue, Jan 22, 2019 at 01:02:54PM -0600, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> 
> 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@xxxxxxxxxxxxx
> Link: https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg02082.html
> Reported-by: xuyandong <xuyandong2@xxxxxxxxxx>
> Tested-by: xuyandong <xuyandong2@xxxxxxxxxx>
> Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
> Cc: Ofer Hayut <ofer@xxxxxxxxxxxxxxxxx>
> Cc: Roy Shterman <roys@xxxxxxxxxxxxxxxxx>
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: Zhou Wang <wangzhou1@xxxxxxxxxxxxx>

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 */
>