Re: [Qemu-devel] [RFC PATCH 2/3] acpi: pc: add fw_cfg device node to ssdt

["Gabriel L. Somlo" <somlo@cmu.edu>]

On Sun, Sep 13, 2015 at 02:45:23PM +0300, Michael S. Tsirkin wrote:
> On Sat, Sep 12, 2015 at 07:30:41PM -0400, Gabriel L. Somlo wrote:
> > Add a fw_cfg device node to the ACPI SSDT. While the guest-side
> > BIOS can't utilize this information (since it has to access the
> > hard-coded fw_cfg device to extract ACPI tables to begin with),
> > having fw_cfg listed in ACPI will help the guest kernel keep a
> > more accurate inventory of in-use IO port regions.
> > 
> > Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
> > ---
> >  hw/i386/acpi-build.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> > 
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index 95e0c65..9d0ec22 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -1071,6 +1071,25 @@ build_ssdt(GArray *table_data, GArray *linker,
> >      aml_append(scope, aml_name_decl("_S5", pkg));
> >      aml_append(ssdt, scope);
> >  
> > +    if (guest_info->fw_cfg) {
> > +        scope = aml_scope("\\_SB");
> > +        dev = aml_device("FWCF");
> > +
> > +        aml_append(dev, aml_name_decl("_HID", aml_string("FWCF0001")));
> 
> Generally that's an illegal HID. If this device has a driver,
> use QEMU as a prefix. Otherwise, use one of the pre-defined ones
> with a PNP ISA ID.

I'm working on a sysfs driver to allow access to fw_cfg files via the
guest kernel (similar to e.g. /sys/firmware/dmi/entries/...). That
probably means I should go with QEMU0002 (0001 is already assigned to
the pvpanic device).

I'll use that in v2, which I'll send out once I get some feedback from
the arm side as well.

Thanks much,
--Gabriel

> > +        /* device present, functioning, decoding, not shown in UI */
> > +        aml_append(dev, aml_name_decl("_STA", aml_int(0xB)));
> > +
> > +        crs = aml_resource_template();
> > +        aml_append(crs,
> > +            aml_io(AML_DECODE16, FW_CFG_IO_BASE, FW_CFG_IO_BASE,
> > +                   0x01, FW_CFG_IO_SIZE)
> > +        );
> > +        aml_append(dev, aml_name_decl("_CRS", crs));
> > +
> > +        aml_append(scope, dev);
> > +        aml_append(ssdt, scope);
> > +    }
> > +
> >      if (misc->applesmc_io_base) {
> >          scope = aml_scope("\\_SB.PCI0.ISA");
> >          dev = aml_device("SMC");
> > -- 
> > 2.4.3