On Fri, Mar 20, 2020 at 06:48:53AM +0100, Gerd Hoffmann wrote:
> > > +static void *pci_mmconfig_addr(u16 bdf, u32 addr)
> > > +{
> > > + if (!mmconfig)
> > > + return NULL;
> > > + return (void*)(mmconfig + ((u32)bdf << 12) + addr);
> > > +}
> > > +
> > > void pci_config_writel(u16 bdf, u32 addr, u32 val)
> > > {
> > > - outl(0x80000000 | (bdf << 8) | (addr & 0xfc), PORT_PCI_CMD);
> > > - outl(val, PORT_PCI_DATA);
> > > + void *mmcfg = pci_mmconfig_addr(bdf, addr);
> > > + if (mmcfg) {
> > > + writel(mmcfg, val);
> > > + } else {
> > > + outl(0x80000000 | (bdf << 8) | (addr & 0xfc), PORT_PCI_CMD);
> > > + outl(val, PORT_PCI_DATA);
> > > + }
> > > }
> >
> > The pci_config_writeX() functions are called from 16-bit mode and
> > 32-big segment mode, so this doesn't look correct to me.
>
> Oh. Wasn't aware of that.
>
> > What device would call the pci_config_writeX() functions frequently
> > enough that performance would matter?
>
> I expect most vmexists come from PCI bar configuration in POST which
> runs in 32bit mode. I think we can restrict this to 32bit mode without
> loosing much.
What is the time improvement for using mmconfig?
> --- a/src/hw/pci.c
> +++ b/src/hw/pci.c
> @@ -18,6 +18,8 @@ static u32 mmconfig;
>
> static void *pci_mmconfig_addr(u16 bdf, u32 addr)
> {
> + if (MODESEGMENT)
> + return NULL;
> if (!mmconfig)
> return NULL;
> return (void*)(mmconfig + ((u32)bdf << 12) + addr);
FWIW, given the low-level nature of these functions, it may be worth
using wrappers like the following:
void pci_config_writel(u16 bdf, u32 addr, u32 val)
{
if (!MODESEGMENT && mmconfig)
pci_mmconfig_writel(bdf, addr, val);
else
pci_ioconfig_writel(bdf, addr, val);
}
-Kevin
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