2015-04-02 21:11:42

by Sean O. Stalley

Subject: [PATCH] Read ID & Pointer from PCI Capabilities List in 1 call

Reading both fields at the same time lets us parse the
list with half the number of configspace reads.

Signed-off-by: Sean O. Stalley <[email protected]>
---
drivers/pci/pci.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 5e3c8e9..db7f3d6 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -145,19 +145,22 @@ static int __pci_find_next_cap_ttl(struct pci_bus *bus, unsigned int devfn,
u8 pos, int cap, int *ttl)
{
u8 id;
+ u16 ent;
+
+ pci_bus_read_config_byte(bus, devfn, pos, &pos);

while ((*ttl)--) {
- pci_bus_read_config_byte(bus, devfn, pos, &pos);
if (pos < 0x40)
break;
pos &= ~3;
- pci_bus_read_config_byte(bus, devfn, pos + PCI_CAP_LIST_ID,
- &id);
+ pci_bus_read_config_word(bus, devfn, pos, &ent);
+
+ id = ent & 0xff;
if (id == 0xff)
break;
if (id == cap)
return pos;
- pos += PCI_CAP_LIST_NEXT;
+ pos = (ent >> 8);
}
return 0;
}
--
1.9.1

2015-04-09 22:13:07

by Bjorn Helgaas

Subject: Re: [PATCH] Read ID & Pointer from PCI Capabilities List in 1 call

On Thu, Apr 02, 2015 at 02:10:19PM -0700, Sean O. Stalley wrote:
> Reading both fields at the same time lets us parse the
> list with half the number of configspace reads.
>
> Signed-off-by: Sean O. Stalley <[email protected]>

Applied to pci/misc for v4.1, thanks Sean!

> ---
> drivers/pci/pci.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 5e3c8e9..db7f3d6 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -145,19 +145,22 @@ static int __pci_find_next_cap_ttl(struct pci_bus *bus, unsigned int devfn,
> u8 pos, int cap, int *ttl)
> {
> u8 id;
> + u16 ent;
> +
> + pci_bus_read_config_byte(bus, devfn, pos, &pos);
>
> while ((*ttl)--) {
> - pci_bus_read_config_byte(bus, devfn, pos, &pos);
> if (pos < 0x40)
> break;
> pos &= ~3;
> - pci_bus_read_config_byte(bus, devfn, pos + PCI_CAP_LIST_ID,
> - &id);
> + pci_bus_read_config_word(bus, devfn, pos, &ent);
> +
> + id = ent & 0xff;
> if (id == 0xff)
> break;
> if (id == cap)
> return pos;
> - pos += PCI_CAP_LIST_NEXT;
> + pos = (ent >> 8);
> }
> return 0;
> }
> --
> 1.9.1
>