Re: [PATCH v3 1/3] PCI: Introduce pcibios_ignore_alignment_request

Bjorn Helgaas
2019-05-29T14:01:02Z

On Tue, May 28, 2019 at 03:36:34PM +1000, Oliver wrote:
> On Tue, May 28, 2019 at 2:03 PM Shawn Anastasio <shawn@anastas.io> wrote:
> >
> > Introduce a new pcibios function pcibios_ignore_alignment_request
> > which allows the PCI core to defer to platform-specific code to
> > determine whether or not to ignore alignment requests for PCI resources.
> >
> > The existing behavior is to simply ignore alignment requests when
> > PCI_PROBE_ONLY is set. This is behavior is maintained by the
> > default implementation of pcibios_ignore_alignment_request.
> >
> > Signed-off-by: Shawn Anastasio <shawn@anastas.io>
> > ---
> > drivers/pci/pci.c | 9 +++++++--
> > include/linux/pci.h | 1 +
> > 2 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 8abc843b1615..8207a09085d1 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -5882,6 +5882,11 @@ resource_size_t __weak pcibios_default_alignment(void)
> > return 0;
> > }
> >
> > +int __weak pcibios_ignore_alignment_request(void)
> > +{
> > + return pci_has_flag(PCI_PROBE_ONLY);
> > +}
> > +
> > #define RESOURCE_ALIGNMENT_PARAM_SIZE COMMAND_LINE_SIZE
> > static char resource_alignment_param[RESOURCE_ALIGNMENT_PARAM_SIZE] = {0};
> > static DEFINE_SPINLOCK(resource_alignment_lock);
> > @@ -5906,9 +5911,9 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
> > p = resource_alignment_param;
> > if (!*p && !align)
> > goto out;
> > - if (pci_has_flag(PCI_PROBE_ONLY)) {
> > + if (pcibios_ignore_alignment_request()) {
> > align = 0;
> > - pr_info_once("PCI: Ignoring requested alignments (PCI_PROBE_ONLY)\n");
> > + pr_info_once("PCI: Ignoring requested alignments\n");
> > goto out;
> > }
>
> I think the logic here is questionable to begin with. If the user has
> explicitly requested re-aligning a resource via the command line then
> we should probably do it even if PCI_PROBE_ONLY is set. When it breaks
> they get to keep the pieces.

I agree. I don't like PCI_PROBE_ONLY in the first place. It's a
sledgehammer approach that doesn't tell us which resource assignments
need to be preserved or why. I'd rather use IORESOURCE_PCI_FIXED and
set it for the BARs where there's actually some sort of
hypervisor/firmware/OS dependency.

If there's a way to avoid another pciobios_*() weak function, that
would also be better.

Bjorn