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vgaarb: use bridges to control VGA routing where possible.
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So in a lot of modern systems, a GPU will always be below a parent bridge that won't share with any other GPUs. This means VGA arbitration on those GPUs can be controlled by using the bridge routing instead of io/mem decodes.

The problem is locating which GPUs share which upstream bridges. This patch attempts to identify all the GPUs which can be controlled via bridges, and ones that can't. This patch endeavours to work out the bridge sharing semantics.

When disabling GPUs via a bridge, it doesn't do irq callbacks or touch the io/mem decodes for the gpu.

Signed-off-by: Dave Airlie <[email protected]>
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@airlied
airlied committed May 4, 2011
1 parent 8116188 commit 3448a19
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Showing 3 changed files with 118 additions and 27 deletions.
113 changes: 99 additions & 14 deletions drivers/gpu/vga/vgaarb.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,7 @@ struct vga_device {
unsigned int mem_lock_cnt; /* legacy MEM lock count */
unsigned int io_norm_cnt; /* normal IO count */
unsigned int mem_norm_cnt; /* normal MEM count */

bool bridge_has_one_vga;
/* allow IRQ enable/disable hook */
void *cookie;
void (*irq_set_state)(void *cookie, bool enable);
Expand Down Expand Up @@ -165,6 +165,8 @@ static struct vga_device *__vga_tryget(struct vga_device *vgadev,
unsigned int wants, legacy_wants, match;
struct vga_device *conflict;
unsigned int pci_bits;
u32 flags = 0;

/* Account for "normal" resources to lock. If we decode the legacy,
* counterpart, we need to request it as well
*/
Expand Down Expand Up @@ -237,16 +239,23 @@ static struct vga_device *__vga_tryget(struct vga_device *vgadev,
/* looks like he doesn't have a lock, we can steal
* them from him
*/
vga_irq_set_state(conflict, false);

flags = 0;
pci_bits = 0;
if (lwants & (VGA_RSRC_LEGACY_MEM|VGA_RSRC_NORMAL_MEM))
pci_bits |= PCI_COMMAND_MEMORY;
if (lwants & (VGA_RSRC_LEGACY_IO|VGA_RSRC_NORMAL_IO))
pci_bits |= PCI_COMMAND_IO;

pci_set_vga_state(conflict->pdev, false, pci_bits,
change_bridge);
if (!conflict->bridge_has_one_vga) {
vga_irq_set_state(conflict, false);
flags |= PCI_VGA_STATE_CHANGE_DECODES;
if (lwants & (VGA_RSRC_LEGACY_MEM|VGA_RSRC_NORMAL_MEM))
pci_bits |= PCI_COMMAND_MEMORY;
if (lwants & (VGA_RSRC_LEGACY_IO|VGA_RSRC_NORMAL_IO))
pci_bits |= PCI_COMMAND_IO;
}

if (change_bridge)
flags |= PCI_VGA_STATE_CHANGE_BRIDGE;

pci_set_vga_state(conflict->pdev, false, pci_bits, flags);
conflict->owns &= ~lwants;
/* If he also owned non-legacy, that is no longer the case */
if (lwants & VGA_RSRC_LEGACY_MEM)
Expand All @@ -261,14 +270,24 @@ static struct vga_device *__vga_tryget(struct vga_device *vgadev,
* also have in "decodes". We can lock resources we don't decode but
* not own them.
*/
flags = 0;
pci_bits = 0;
if (wants & (VGA_RSRC_LEGACY_MEM|VGA_RSRC_NORMAL_MEM))
pci_bits |= PCI_COMMAND_MEMORY;
if (wants & (VGA_RSRC_LEGACY_IO|VGA_RSRC_NORMAL_IO))
pci_bits |= PCI_COMMAND_IO;
pci_set_vga_state(vgadev->pdev, true, pci_bits, !!(wants & VGA_RSRC_LEGACY_MASK));

vga_irq_set_state(vgadev, true);
if (!vgadev->bridge_has_one_vga) {
flags |= PCI_VGA_STATE_CHANGE_DECODES;
if (wants & (VGA_RSRC_LEGACY_MEM|VGA_RSRC_NORMAL_MEM))
pci_bits |= PCI_COMMAND_MEMORY;
if (wants & (VGA_RSRC_LEGACY_IO|VGA_RSRC_NORMAL_IO))
pci_bits |= PCI_COMMAND_IO;
}
if (!!(wants & VGA_RSRC_LEGACY_MASK))
flags |= PCI_VGA_STATE_CHANGE_BRIDGE;

pci_set_vga_state(vgadev->pdev, true, pci_bits, flags);

if (!vgadev->bridge_has_one_vga) {
vga_irq_set_state(vgadev, true);
}
vgadev->owns |= (wants & vgadev->decodes);
lock_them:
vgadev->locks |= (rsrc & VGA_RSRC_LEGACY_MASK);
Expand Down Expand Up @@ -421,6 +440,62 @@ void vga_put(struct pci_dev *pdev, unsigned int rsrc)
}
EXPORT_SYMBOL(vga_put);

/* Rules for using a bridge to control a VGA descendant decoding:
if a bridge has only one VGA descendant then it can be used
to control the VGA routing for that device.
It should always use the bridge closest to the device to control it.
If a bridge has a direct VGA descendant, but also have a sub-bridge
VGA descendant then we cannot use that bridge to control the direct VGA descendant.
So for every device we register, we need to iterate all its parent bridges
so we can invalidate any devices using them properly.
*/
static void vga_arbiter_check_bridge_sharing(struct vga_device *vgadev)
{
struct vga_device *same_bridge_vgadev;
struct pci_bus *new_bus, *bus;
struct pci_dev *new_bridge, *bridge;

vgadev->bridge_has_one_vga = true;

if (list_empty(&vga_list))
return;

/* okay iterate the new devices bridge hierarachy */
new_bus = vgadev->pdev->bus;
while (new_bus) {
new_bridge = new_bus->self;

if (new_bridge) {
/* go through list of devices already registered */
list_for_each_entry(same_bridge_vgadev, &vga_list, list) {
bus = same_bridge_vgadev->pdev->bus;
bridge = bus->self;

/* see if the share a bridge with this device */
if (new_bridge == bridge) {
/* if their direct parent bridge is the same
as any bridge of this device then it can't be used
for that device */
same_bridge_vgadev->bridge_has_one_vga = false;
}

/* now iterate the previous devices bridge hierarchy */
/* if the new devices parent bridge is in the other devices
hierarchy then we can't use it to control this device */
while (bus) {
bridge = bus->self;
if (bridge) {
if (bridge == vgadev->pdev->bus->self)
vgadev->bridge_has_one_vga = false;
}
bus = bus->parent;
}
}
}
new_bus = new_bus->parent;
}
}

/*
* Currently, we assume that the "initial" setup of the system is
* not sane, that is we come up with conflicting devices and let
Expand Down Expand Up @@ -500,6 +575,8 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
vga_default = pci_dev_get(pdev);
#endif

vga_arbiter_check_bridge_sharing(vgadev);

/* Add to the list */
list_add(&vgadev->list, &vga_list);
vga_count++;
Expand Down Expand Up @@ -1222,6 +1299,7 @@ static int __init vga_arb_device_init(void)
{
int rc;
struct pci_dev *pdev;
struct vga_device *vgadev;

rc = misc_register(&vga_arb_device);
if (rc < 0)
Expand All @@ -1238,6 +1316,13 @@ static int __init vga_arb_device_init(void)
vga_arbiter_add_pci_device(pdev);

pr_info("vgaarb: loaded\n");

list_for_each_entry(vgadev, &vga_list, list) {
if (vgadev->bridge_has_one_vga)
pr_info("vgaarb: bridge control possible %s\n", pci_name(vgadev->pdev));
else
pr_info("vgaarb: no bridge control possible %s\n", pci_name(vgadev->pdev));
}
return rc;
}
subsys_initcall(vga_arb_device_init);
25 changes: 14 additions & 11 deletions drivers/pci/pci.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2875,31 +2875,34 @@ static int pci_set_vga_state_arch(struct pci_dev *dev, bool decode,
* @dev: the PCI device
* @decode: true = enable decoding, false = disable decoding
* @command_bits: PCI_COMMAND_IO and/or PCI_COMMAND_MEMORY
* @change_bridge: traverse ancestors and change bridges
* @change_bridge_flags: traverse ancestors and change bridges
* CHANGE_BRIDGE_ONLY / CHANGE_BRIDGE
*/
int pci_set_vga_state(struct pci_dev *dev, bool decode,
unsigned int command_bits, bool change_bridge)
unsigned int command_bits, u32 flags)
{
struct pci_bus *bus;
struct pci_dev *bridge;
u16 cmd;
int rc;

WARN_ON(command_bits & ~(PCI_COMMAND_IO|PCI_COMMAND_MEMORY));
WARN_ON((flags & PCI_VGA_STATE_CHANGE_DECODES) & (command_bits & ~(PCI_COMMAND_IO|PCI_COMMAND_MEMORY)));

/* ARCH specific VGA enables */
rc = pci_set_vga_state_arch(dev, decode, command_bits, change_bridge);
rc = pci_set_vga_state_arch(dev, decode, command_bits, flags);
if (rc)
return rc;

pci_read_config_word(dev, PCI_COMMAND, &cmd);
if (decode == true)
cmd |= command_bits;
else
cmd &= ~command_bits;
pci_write_config_word(dev, PCI_COMMAND, cmd);
if (flags & PCI_VGA_STATE_CHANGE_DECODES) {
pci_read_config_word(dev, PCI_COMMAND, &cmd);
if (decode == true)
cmd |= command_bits;
else
cmd &= ~command_bits;
pci_write_config_word(dev, PCI_COMMAND, cmd);
}

if (change_bridge == false)
if (!(flags & PCI_VGA_STATE_CHANGE_BRIDGE))
return 0;

bus = dev->bus;
Expand Down
7 changes: 5 additions & 2 deletions include/linux/pci.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -915,8 +915,11 @@ int pci_cfg_space_size_ext(struct pci_dev *dev);
int pci_cfg_space_size(struct pci_dev *dev);
unsigned char pci_bus_max_busnr(struct pci_bus *bus);

#define PCI_VGA_STATE_CHANGE_BRIDGE (1 << 0)
#define PCI_VGA_STATE_CHANGE_DECODES (1 << 1)

int pci_set_vga_state(struct pci_dev *pdev, bool decode,
unsigned int command_bits, bool change_bridge);
unsigned int command_bits, u32 flags);
/* kmem_cache style wrapper around pci_alloc_consistent() */

#include <linux/pci-dma.h>
Expand Down Expand Up @@ -1061,7 +1064,7 @@ static inline int pci_proc_domain(struct pci_bus *bus)

/* some architectures require additional setup to direct VGA traffic */
typedef int (*arch_set_vga_state_t)(struct pci_dev *pdev, bool decode,
unsigned int command_bits, bool change_bridge);
unsigned int command_bits, u32 flags);
extern void pci_register_set_vga_state(arch_set_vga_state_t func);

#else /* CONFIG_PCI is not enabled */
Expand Down

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