Re: [PATCH V2 22/23] pci, acpi: Match PCI config space accessors against platfrom specific quirks.

[Mark Salter]

On Wed, 2015-12-16 at 16:16 +0100, Tomasz Nowicki wrote:
> Some platforms may not be fully compliant with generic set of PCI config
> accessors. For these cases we implement the way to overwrite accessors
> set before PCI buses enumeration. Algorithm that overwrite accessors
> matches against platform ID (DMI), domain and bus number, hopefully
> enough for all cases. All quirks can be defined using:
> DECLARE_ACPI_MCFG_FIXUP() and keep self contained.
> 
> example:
> 
> static const struct dmi_system_id yyy[] = {
> ÂÂÂÂÂÂÂÂ{
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ.ident = "<Platform ident string>",
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ.callback = <handler>,
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ.matches = {
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂDMI_MATCH(DMI_SYS_VENDOR, "<system vendor>"),
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂDMI_MATCH(DMI_PRODUCT_NAME, "<product name>"),
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂDMI_MATCH(DMI_PRODUCT_VERSION, "product version"),
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ},
> ÂÂÂÂÂÂÂÂ},
> ÂÂÂÂÂÂÂÂ{ }
> };
> 

This seems awkward to me in the case where the quirk is SoC-based and there
may be multiple platforms affected. Needing a DECLARE_ACPI_MCFG_FIXUP for
each platform using such a SoC (i.e. Mustang and Moonshot) doesn't seem
right. In that case, I think it'd be better to check CPUID and possibly
some SoC register to cover all platforms affected.

Also, there doesn't seem to be a way to connect a given quirk check to the
MCFG/device requesting the ops. So if there is a platform with multiple PCIE
roots and not all of them have quirks, how does one no whether to override the
default ecam ops?