On Tue, 12 Jan 2021 at 23:49, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Sat, Jan 09, 2021 at 10:53:53AM +0100, Ard Biesheuvel wrote:
> > The _DSM #5 method in the ACPI host bridge object tells us whether the
> > OS is permitted to deviate from the resource assignment configured by
> > the firmware. If this is not the case, we should not permit drivers to
> > resize BARs on the fly. So make pci_resize_resource() take this into
> > account.
> >
> > Cc: <stable@xxxxxxxxxxxxxxx> # v5.4+
> > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
>
> Capitalized subject to match convention and applied to pci/resource
> for v5.11, thanks!
>
> Is there an email, bug report, etc that prompted this change?
>
No, I was just reviewing the recent Tianocore changes to perform BAR
resizing before resource assignment even takes places, which is
obviously a more appropriate time to do it, as it does not require the
OS to modify the firmware configuration at all. This reminded me of
_DSM #5 and the fact that the OS may not even be permitted to make any
changes.
> > ---
> > drivers/pci/setup-res.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> > index 43eda101fcf4..3b38be081e93 100644
> > --- a/drivers/pci/setup-res.c
> > +++ b/drivers/pci/setup-res.c
> > @@ -410,10 +410,16 @@ EXPORT_SYMBOL(pci_release_resource);
> > int pci_resize_resource(struct pci_dev *dev, int resno, int size)
> > {
> > struct resource *res = dev->resource + resno;
> > + struct pci_host_bridge *host;
> > int old, ret;
> > u32 sizes;
> > u16 cmd;
> >
> > + /* Check if we must preserve the firmware's resource assignment */
> > + host = pci_find_host_bridge(dev->bus);
> > + if (host->preserve_config)
> > + return -ENOTSUPP;
> > +
> > /* Make sure the resource isn't assigned before resizing it. */
> > if (!(res->flags & IORESOURCE_UNSET))
> > return -EBUSY;
> > --
> > 2.17.1
> >
