Re: [Qemu-devel] [PATCH v3 26/32] nvdimm: save arg3 for NVDIMM device _DSM method

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

On Mon, Oct 19, 2015 at 03:14:28PM +0800, Xiao Guangrong wrote:
> 
> 
> On 10/19/2015 02:50 PM, Michael S. Tsirkin wrote:
> >On Sun, Oct 11, 2015 at 11:52:58AM +0800, Xiao Guangrong wrote:
> >>Check if the input Arg3 is valid then store it into dsm_in if needed
> >>
> >>We only do the save on NVDIMM device since we are not going to support any
> >>function on root device
> >>
> >>Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> >>---
> >>  hw/mem/nvdimm/acpi.c | 21 ++++++++++++++++++++-
> >>  1 file changed, 20 insertions(+), 1 deletion(-)
> >>
> >>diff --git a/hw/mem/nvdimm/acpi.c b/hw/mem/nvdimm/acpi.c
> >>index d9fa0fd..3b9399c 100644
> >>--- a/hw/mem/nvdimm/acpi.c
> >>+++ b/hw/mem/nvdimm/acpi.c
> >>@@ -442,7 +442,7 @@ static void build_nvdimm_devices(NVDIMMState *state, GSList *device_list,
> >>          int slot = object_property_get_int(OBJECT(nvdimm), DIMM_SLOT_PROP,
> >>                                             NULL);
> >>          uint32_t handle = nvdimm_slot_to_handle(slot);
> >>-        Aml *dev, *method;
> >>+        Aml *dev, *method, *ifctx;
> >>
> >>          dev = aml_device("NV%02X", slot);
> >>          aml_append(dev, aml_name_decl("_ADR", aml_int(handle)));
> >>@@ -452,6 +452,24 @@ static void build_nvdimm_devices(NVDIMMState *state, GSList *device_list,
> >>          method = aml_method("_DSM", 4);
> >>          {
> >>              SAVE_ARG012_HANDLE_LOCK(method, aml_int(handle));
> >>+
> >>+            /* Arg3 is passed as Package and it has one element? */
> >>+            ifctx = aml_if(aml_and(aml_equal(aml_object_type(aml_arg(3)),
> >>+                                             aml_int(4)),
> >>+                                   aml_equal(aml_sizeof(aml_arg(3)),
> >
> >aml_arg(3) is used many times below.
> >Pls give it a name that makes sense (not arg3! what is it for?)
> >
> 
> Er. aml_arg(3) is just the fourth parameter of _DSM method. Will add some
> comments:
> 
> /*
>  * The fourth parameter (Arg3) of _DMS is a package which contains a buffer, the
>  * layout of the buffer is specified by UUID (Arg0), Revision ID (Arg1) and
>  * Function Index (Arg2) which are documented in the DSM specification.
>  */
> 
> >>+                                             aml_int(1))));
> >
> >Pls document AML constants used.
> >Like this:
> >
> >             ifctx = aml_if(aml_and(aml_equal(aml_object_type(aml_arg(3)),
> >                                              aml_int(4 /* 4 - Package */) ),
> >                                    aml_equal(aml_sizeof(aml_arg(3)),
> >                                              aml_int(1))));
> >
> >>+            {
> >>+                /* Local0 = Index(Arg3, 0) */
> >>+                aml_append(ifctx, aml_store(aml_index(aml_arg(3), aml_int(0)),
> >>+                                            aml_local(0)));
> >>+                /* Local3 = DeRefOf(Local0) */
> >>+                aml_append(ifctx, aml_store(aml_derefof(aml_local(0)),
> >>+                                            aml_local(3)));
> >>+                /* ARG3 = Local3 */
> >>+                aml_append(ifctx, aml_store(aml_local(3), aml_name("ARG3")));
> >
> >This isn't a good way to comment things: you are
> >just adding ASL before the equivalent C.
> >Pls document what's going on.
> >
> 
> Okay... i just thought C is little readable than AML. Will change the comment
> to:
> 
> /* fetch buffer from the package (Arg3) and store it to DSM memory. */
> 
> Thanks.

You can use variables to make the logic clear. E.g.:

	Aml *pckg = aml_arg(3);
	Aml *pckg_idx = aml_local(0);
	Aml *pckg_buf = aml_local(3);

	aml_append(ifctx, aml_store(aml_index(pckg, aml_int(0)), pckg_idx);
	aml_append(ifctx, aml_store(aml_derefof(pckg_idx), pckg_buf));


This is also better than repeating aml_arg(3) many times.

-- 
MST