RE: [PATCH 10/10] hw/pci-host: Emit a _DSM on pxb-cxl to preserve firmware PCI config

> -----Original Message-----
> From: Junjie Cao <[email protected]>
> Sent: 18 August 2026 15:23
> To: Manish Honap <[email protected]>
> Cc: [email protected]; Ankit Agrawal <[email protected]>;
> [email protected]; [email protected]; [email protected];
> Srirangan Madhavan <[email protected]>;
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; Krishnakant Jaju <[email protected]>; Vikram Sethi
> <[email protected]>; Zhi Wang <[email protected]>; [email protected];
> [email protected]
> Subject: Re: [PATCH 10/10] hw/pci-host: Emit a _DSM on pxb-cxl to
> preserve firmware PCI config
> 
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> 
> 
> Hi Manish,
> 
> On Thu, 13 Aug 2026 18:36:23 +0530, Manish Honap wrote:
> > -void build_cxl_osc_method(Aml *dev)
> > +void acpi_dsdt_add_cxl_host_bridge_methods(Aml *dev, bool
> > +preserve_config)
> >  {
> >      aml_append(dev, aml_name_decl("SUPP", aml_int(0)));
> >      aml_append(dev, aml_name_decl("CTRL", aml_int(0)));
> >      aml_append(dev, aml_name_decl("SUPC", aml_int(0)));
> >      aml_append(dev, aml_name_decl("CTRC", aml_int(0)));
> >      aml_append(dev, __build_cxl_osc_method());
> > +    aml_append(dev,
> > + build_pci_host_bridge_dsm_method(preserve_config));
> 
> This is the bios-tables refresh the cover lists as pending:
> /x86_64/acpi/q35/cxl and /x86_64/acpi/q35/acpihmat-genericx both hit the
> all_tables_match assertion with a DSDT mismatch, and the asl diff is
> exactly this _DSM under the pxb-cxl device (12638 -> 12684 bytes on the
> acpihmat-generic-x variant). The g_assert aborts the test binary, so a
> full run only reports the first case.
> 
> With preserve_config=false the method advertises no functions and
> returns a zero buffer for every function, so the x86 half of the change
> is dead AML plus golden-table churn. Append the _DSM only when
> preserve_config is set: the x86 tables stay untouched and the pending
> refresh drops out. Otherwise the usual three-patch bios-tables update
> needs to ride in this series.
> 
> aarch64/virt has no CXL golden files, so nothing catches the arm side
> either way.

Agreed, I will append the _DSM only when preserve_config is set.

> 
> Many thanks,
> Junjie