[PATCH v4] hw/cxl: Add QTG _DSM support for ACPI0017 device

[Dave Jiang]

Add a simple _DSM call support for the ACPI0017 device to return fake QTG
ID values of 0 and 1 in all cases. This for _DSM plumbing testing from the OS.

Following edited for readability

Device (CXLM)
{
    Name (_HID, "ACPI0017")  // _HID: Hardware ID
...
    Method (_DSM, 4, Serialized)  // _DSM: Device-Specific Method
    {
        If ((Arg0 == ToUUID ("f365f9a6-a7de-4071-a66a-b40c0b4f8e52")))
        {
            If ((Arg2 == Zero))
            {
                Return (Buffer (One) { 0x01 })
            }

            If ((Arg2 == One))
            {
                Return (Package (0x02)
                {
                    One,
                    Package (0x02)
                    {
                        Zero,
                        One
                    }
                })
            }
        }
    }

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

--
v4: Change to package of ints rather than buffers. Also moved to 2 QTG IDs
to improve kernel side testing. Tested on x86 qemu guest against kernel
QTG ID _DSM parsing code to be upstreamed.

v3: Fix output assignment to be BE host friendly. Fix typo in comment.
According to the CXL spec, the DSM output should be 1 WORD to indicate
the max suppoted QTG ID and a package of 0 or more WORDs for the QTG IDs.
In this dummy impementation, we have first WORD with a 1 to indcate max
supprted QTG ID of 1. And second WORD in a package to indicate the QTG
ID of 0.

v2: Minor edit to drop reference to switches in patch description.
Message-Id: <20230904161847.18468-3-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/acpi/cxl.c         |   69 +++++++++++++++++++++++++++++++++++++++++++++++++
 hw/i386/acpi-build.c  |    1 +
 include/hw/acpi/cxl.h |    1 +
 3 files changed, 71 insertions(+)

diff --git a/hw/acpi/cxl.c b/hw/acpi/cxl.c
index 92b46bc9323b..9cd7905ea25a 100644
--- a/hw/acpi/cxl.c
+++ b/hw/acpi/cxl.c
@@ -30,6 +30,75 @@
 #include "qapi/error.h"
 #include "qemu/uuid.h"
 
+void build_cxl_dsm_method(Aml *dev)
+{
+    Aml *method, *ifctx, *ifctx2;
+
+    method = aml_method("_DSM", 4, AML_SERIALIZED);
+    {
+        Aml *function, *uuid;
+
+        uuid = aml_arg(0);
+        function = aml_arg(2);
+        /* CXL spec v3.0 9.17.3.1 _DSM Function for Retrieving QTG ID */
+        ifctx = aml_if(aml_equal(
+            uuid, aml_touuid("F365F9A6-A7DE-4071-A66A-B40C0B4F8E52")));
+
+        /* Function 0, standard DSM query function */
+        ifctx2 = aml_if(aml_equal(function, aml_int(0)));
+        {
+            uint8_t byte_list[1] = { 0x01 }; /* function 1 only */
+
+            aml_append(ifctx2,
+                       aml_return(aml_buffer(sizeof(byte_list), byte_list)));
+        }
+        aml_append(ifctx, ifctx2);
+
+        /*
+         * Function 1
+         * Creating a package with static values. The max supported QTG ID will
+         * be 1 and recommended QTG IDs are 0 and then 1.
+         * The values here are statically created to simplify emulation. Values
+         * from a real BIOS would be determined by the performance of all the
+         * present CXL memory and then assigned.
+         */
+        ifctx2 = aml_if(aml_equal(function, aml_int(1)));
+        {
+            Aml *pak, *pak1;
+
+            /*
+             * Return: A package containing two elements - a WORD that returns
+             * the maximum throttling group that the platform supports, and a
+             * package containing the QTG ID(s) that the platform recommends.
+             * Package {
+             *     Max Supported QTG ID
+             *     Package {QTG Recommendations}
+             * }
+             *
+             * While the SPEC specified WORD that hints at the value being
+             * 16bit, the ACPI dump of BIOS DSDT table showed that the values
+             * are integers with no specific size specification. aml_int() will
+             * be used for the values.
+             */
+            pak1 = aml_package(2);
+            /* Set QTG ID of 0 */
+            aml_append(pak1, aml_int(0));
+            /* Set QTG ID of 1 */
+            aml_append(pak1, aml_int(1));
+
+            pak = aml_package(2);
+            /* Set Max QTG 1 */
+            aml_append(pak, aml_int(1));
+            aml_append(pak, pak1);
+
+            aml_append(ifctx2, aml_return(pak));
+        }
+        aml_append(ifctx, ifctx2);
+    }
+    aml_append(method, ifctx);
+    aml_append(dev, method);
+}
+
 static void cedt_build_chbs(GArray *table_data, PXBCXLDev *cxl)
 {
     PXBDev *pxb = PXB_DEV(cxl);
diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 95199c89008a..692af40b1a75 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -1422,6 +1422,7 @@ static void build_acpi0017(Aml *table)
     method = aml_method("_STA", 0, AML_NOTSERIALIZED);
     aml_append(method, aml_return(aml_int(0x01)));
     aml_append(dev, method);
+    build_cxl_dsm_method(dev);
 
     aml_append(scope, dev);
     aml_append(table, scope);
diff --git a/include/hw/acpi/cxl.h b/include/hw/acpi/cxl.h
index acf441888683..8f22c71530d8 100644
--- a/include/hw/acpi/cxl.h
+++ b/include/hw/acpi/cxl.h
@@ -25,5 +25,6 @@ void cxl_build_cedt(GArray *table_offsets, GArray *table_data,
                     BIOSLinker *linker, const char *oem_id,
                     const char *oem_table_id, CXLState *cxl_state);
 void build_cxl_osc_method(Aml *dev);
+void build_cxl_dsm_method(Aml *dev);
 
 #endif