Re: [Qemu-arm] [Qemu-devel] [PATCH v2 6/8] hw: arm: Support both legacy and current RSDP build

[Samuel Ortiz <sameo@linux.intel.com>]

On Thu, Nov 29, 2018 at 03:42:43PM +0100, Andrew Jones wrote:
> On Thu, Nov 29, 2018 at 02:24:26PM +0100, Samuel Ortiz wrote:
> > We add the ability to build legacy or current RSDP tables, based on the
> > AcpiRsdpData revision field passed to build_rsdp().
> > Although arm/virt only uses RSDP v2, adding that capability to
> > build_rsdp will allow us to share the RSDP build code between ARM and x86.
> > 
> > Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
> > ---
> >  hw/arm/virt-acpi-build.c | 37 ++++++++++++++++++++++++++-----------
> >  1 file changed, 26 insertions(+), 11 deletions(-)
> > 
> > diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> > index 4782aea4fe..e1338b6f5a 100644
> > --- a/hw/arm/virt-acpi-build.c
> > +++ b/hw/arm/virt-acpi-build.c
> > @@ -378,23 +378,38 @@ build_rsdp(GArray *tbl, BIOSLinker *linker, AcpiRsdpData *rsdp_data)
> >      g_array_append_vals(tbl, rsdp_data->oem_id, 6); /* OEMID */
> >      build_append_int_noprefix(tbl, rsdp_data->revision, 1); /* Revision */
> >      build_append_int_noprefix(tbl, 0, 4); /* RsdtAddress */
> > -    build_append_int_noprefix(tbl, 36, 4); /* Length */
> > -
> > -    /* XSDT address to be filled by guest linker */
> > -    build_append_int_noprefix(tbl, 0, 8); /* XsdtAddress */
> > -    bios_linker_loader_add_pointer(linker, ACPI_BUILD_RSDP_FILE,
> > -                                   24, 8,
> > -                                   ACPI_BUILD_TABLE_FILE,
> > -                                   *rsdp_data->xsdt_tbl_offset);
> > -
> > -    build_append_int_noprefix(tbl, 0, 1); /* Extended Checksum */
> > -    build_append_int_noprefix(tbl, 0, 3); /* Reserved */
> > +    if (rsdp_data->rsdt_tbl_offset) {
> 
> I see why a pointer was used now. Using a pointer ensures a zero
> offset won't fail this test. However the test could be replaced with
> rsdp_data->revision == 0.
> 
> > +        /* RSDT address to be filled by guest linker */
> > +        bios_linker_loader_add_pointer(linker,
> > +                                       ACPI_BUILD_RSDP_FILE, 16, 4,
> > +                                       ACPI_BUILD_TABLE_FILE,
> > +                                       *rsdp_data->rsdt_tbl_offset);
> > +    }
> >  
> >      /* Checksum to be filled by guest linker */
> >      bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE,
> >                                      0, 20, /* ACPI rev 1.0 RSDP size */
> >                                      8);
> >  
> > +    if (rsdp_data->revision == 0) {
> > +        /* ACPI 1.0 RSDP, we're done */
> > +        return;
> > +    }
> > +
> > +    /* The RSDP revision is 2 and later, we must have an XSDT pointer */
> > +    g_assert(rsdp_data->xsdt_tbl_offset != NULL);
> 
> So here's the justification for the pointers. We sanity check the callers.
We could sanity check the callers without pointers as well, I don't
think there's a strong advantage for pointers here, except consistence.


> We're missing the (rsdp_data->revision == 0 && rsdp_data->rsdt_tbl_offset)
> sanity check though.
I think there's nothing preventing a caller to include both rsdt and
xsdt if it wants to be able to run on both < 2.0 and 2.0+ platforms with
the same table. So if rsdt is set we should add it, regardless of the revision.

Cheers,
Samuel.