Re: [Qemu-devel] [PATCH V3] hw/pxb-pcie: fix PCI Express hotplug support

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Feb 27, 2017 at 03:12:26PM +0200, Marcel Apfelbaum wrote:
> Add the missing osc method for pxb-pcie devices as APCI spec recommends,
> see 6.2.10.3 OSC Implementation Example for PCI Host Bridge Devices, ACPI 5.0:
> 
>     It is recommended that a machine with multiple host bridge devices
>     should report the same capabilities for all host bridges, and also
>     negotiate control of the features described in the Control Field in
>     the same way for all host bridges.
> 
> Reviewed-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
> ---
> 
> Note to maintainer:
>  Please update ACPI test files.
> 
> V2 -> V3:
>       - Modified comment (Igor)
> 
> V1 -> V2:
>     Addressed Michael S. Tsirkin's comments:
>       - Added documentation to q35 osc function
>       - Made _osc serialized. I did not add compat property
>         since it seems guest OSs do not care anyway about the OSC
>         being serialized.
>       - Kept the SUPP field even if is not used and also
>         left both SUPP and CTRL out of the _osc because all
>         systems I checked and the ACPI spec keep them that way,
>         maybe is some kind of documentation contract.
> 
> Thanks,
> Marcel
> 
> 
>  hw/i386/acpi-build.c | 41 +++++++++++++++++++++++++++++++++++------
>  1 file changed, 35 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index 1c928ab..ad3f233 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -1796,7 +1796,7 @@ static void build_piix4_pci_hotplug(Aml *table)
>      aml_append(table, scope);
>  }
>  
> -static Aml *build_q35_osc_method(void)
> +static void build_q35_osc_method(Aml *dev)

This does more than just build _OSC so please
give it a better name.

>  {
>      Aml *if_ctx;
>      Aml *if_ctx2;
> @@ -1805,7 +1805,35 @@ static Aml *build_q35_osc_method(void)
>      Aml *a_cwd1 = aml_name("CDW1");
>      Aml *a_ctrl = aml_name("CTRL");
>  
> -    method = aml_method("_OSC", 4, AML_NOTSERIALIZED);
> +    /*
> +     * Bits defined in the Support Field provide information
> +     * regarding OS supported features.
> +     *
> +     * This field is not actually used and can be removed,
> +     * however it appears even if unused on most DSDTs.

What does this mean? Our _OSC method uses these,
that's why we have them. How can you just remove them?

I think you mean we could remove the code writing to it.
I don't think keeping it around is justified.
Same applies to CTRL btw. We could use a local variable
instead.


> +     *
> +     * See:
> +     *     Table 6-148 Interpretation of _OSC Support Field,
> +     *     Passed in via the 2nd dword in Arg3, APCI 5.0

Why 5.0? This is not how we do it. Pls find the earliest spec version
that has this. 3.0?

> +     */
> +    aml_append(dev, aml_name_decl("SUPP", aml_int(0)));
> +
> +    /*
> +     * Bits defined in the Control Field are used to submit
> +     * request by the OS for control/handling of the associated feature
> +     *
> +     * See: Table 6-149 Interpretation of _OSC Control Field,
> +     *      Passed in via Arg3, ACPI 5.0
> +     *      Table 6-150 Interpretation of _OSC Control Field,
> +     *      Returned Value, APCI 5.0
> +     */
> +    aml_append(dev, aml_name_decl("CTRL", aml_int(0)));
> +
> +
> +   /*
> +    * 6.2.10 _OSC (Operating System Capabilities), APCI 5.0
> +    */

Same here.

> +    method = aml_method("_OSC", 4, AML_SERIALIZED);
>      aml_append(method, aml_create_dword_field(aml_arg(3), aml_int(0), "CDW1"));
>  
>      if_ctx = aml_if(aml_equal(
> @@ -1842,7 +1870,7 @@ static Aml *build_q35_osc_method(void)
>      aml_append(method, else_ctx);
>  
>      aml_append(method, aml_return(aml_arg(3)));
> -    return method;
> +    aml_append(dev, method);

If you drop SUPP and CTRL then you can keep it simple, right?

>  }
>  
>  static void
> @@ -1898,9 +1926,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
>          aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
>          aml_append(dev, aml_name_decl("_ADR", aml_int(0)));
>          aml_append(dev, aml_name_decl("_UID", aml_int(1)));
> -        aml_append(dev, aml_name_decl("SUPP", aml_int(0)));
> -        aml_append(dev, aml_name_decl("CTRL", aml_int(0)));
> -        aml_append(dev, build_q35_osc_method());
> +        build_q35_osc_method(dev);
>          aml_append(sb_scope, dev);
>          aml_append(dsdt, sb_scope);
>  
> @@ -1964,6 +1990,9 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
>              aml_append(dev, aml_name_decl("_UID", aml_int(bus_num)));
>              aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A03")));
>              aml_append(dev, aml_name_decl("_BBN", aml_int(bus_num)));
> +            if (pci_bus_is_express(bus)) {
> +                build_q35_osc_method(dev);
> +            }
>  
>              if (numa_node != NUMA_NODE_UNASSIGNED) {
>                  aml_append(dev, aml_name_decl("_PXM", aml_int(numa_node)));
> -- 
> 2.5.5


so how about

--->

acpi: simplify _OSC

Our _OSC method has a bunch of unused code loading data
into external CTRL and SUPP fields which are then never
used. Drop this in favor of a single local variable.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

---

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index db04cf5..efbbfcb 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -1804,7 +1804,7 @@ static Aml *build_q35_osc_method(void)
     Aml *else_ctx;
     Aml *method;
     Aml *a_cwd1 = aml_name("CDW1");
-    Aml *a_ctrl = aml_name("CTRL");
+    Aml *a_ctrl = aml_local(0);
 
     method = aml_method("_OSC", 4, AML_NOTSERIALIZED);
     aml_append(method, aml_create_dword_field(aml_arg(3), aml_int(0), "CDW1"));
@@ -1814,7 +1814,6 @@ static Aml *build_q35_osc_method(void)
     aml_append(if_ctx, aml_create_dword_field(aml_arg(3), aml_int(4), "CDW2"));
     aml_append(if_ctx, aml_create_dword_field(aml_arg(3), aml_int(8), "CDW3"));
 
-    aml_append(if_ctx, aml_store(aml_name("CDW2"), aml_name("SUPP")));
     aml_append(if_ctx, aml_store(aml_name("CDW3"), a_ctrl));
 
     /*
@@ -1899,8 +1898,6 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
         aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
         aml_append(dev, aml_name_decl("_ADR", aml_int(0)));
         aml_append(dev, aml_name_decl("_UID", aml_int(1)));
-        aml_append(dev, aml_name_decl("SUPP", aml_int(0)));
-        aml_append(dev, aml_name_decl("CTRL", aml_int(0)));
         aml_append(dev, build_q35_osc_method());
         aml_append(sb_scope, dev);
         aml_append(dsdt, sb_scope);