Re: [RFC PATCH v4 3/5] PCI: Check platform specific ECAM quirks

[Tomasz Nowicki]

On 28.06.2016 18:12, Duc Dang wrote:
> On Tue, Jun 28, 2016 at 6:04 AM, Christopher Covington
> <cov@xxxxxxxxxxxxxx> wrote:
> > Hi Tomasz,
> >
> > On 06/28/2016 03:54 AM, Tomasz Nowicki wrote:
> >
> > > diff --git a/drivers/pci/host/mcfg-quirks.c b/drivers/pci/host/mcfg-quirks.c
> > > new file mode 100644
> > > index 0000000..fb2b184
> > > --- /dev/null
> > > +++ b/drivers/pci/host/mcfg-quirks.c
> > > @@ -0,0 +1,88 @@
> >
> > > +static bool pci_mcfg_fixup_match(struct pci_cfg_fixup *f,
> > > +                              struct acpi_table_header *mcfg_header)
> > > +{
> > > +     int olen = min_t(u8, strlen(f->oem_id), ACPI_OEM_ID_SIZE);
> > > +     int tlen = min_t(u8, strlen(f->oem_table_id), ACPI_OEM_TABLE_ID_SIZE);
> > > +
> > > +     return (!strncmp(f->oem_id, mcfg_header->oem_id, olen) &&
> > > +             !strncmp(f->oem_table_id, mcfg_header->oem_table_id, tlen) &&
> > > +             f->oem_revision == mcfg_header->oem_revision);
> > > +}
> >
> > Ard's comments on v3 included:
> >
> > "... exact OEM table/rev id matches ..."
> > "... substring match ... out of the question ..."
> >
> > I originally advocated the substring match approach because
> > space-padding the input strings was unfamiliar. But given that some
> > vendors have a "PLAT    " then "PLAT2   " naming scheme, where the
> > former needs quirks and the latter (hopefully) doesn't, I agree with Ard
> > and think space-padded inputs is the better way to go. Sorry for the
> > lack of foresight.
>
> I think having OEM Table ID as "PLAT   " and then "PLAT2  " (the the
> next version of the SoC)
> is common. So yes, matching full string is better as we can use "PLAT2  "
> in MCFG table and not worry about the "PLAT" sub-string match causes the quirk
> to be applied unintentionally.

Sorry, I forgot to address Ard's comment.

Note that platforms already shipped where OEM string has no padding will 
have change the firmware or add 0 padding to our quirk array IDs.
So how about:

static bool pci_mcfg_fixup_match(struct pci_cfg_fixup *f,
				 struct acpi_table_header *mcfg_header)
{
	int olen = strnlen(mcfg_header->oem_id, ACPI_OEM_ID_SIZE);
	int tlen = strnlen(mcfg_header->oem_table_id, ACPI_OEM_TABLE_ID_SIZE);

	if (olen != strlen(f->oem_id) || tlen != strlen(f->oem_table_id))
		return false;

	return (!strncmp(f->oem_id, mcfg_header->oem_id, olen) &&
		!strncmp(f->oem_table_id, mcfg_header->oem_table_id, tlen) &&
		f->oem_revision == mcfg_header->oem_revision);
}

This should work for all cases:
1. "PLAT"
2. "PLAT    " padding
3. No need to change existing firmware

Tomasz