[PATCH v4] hw/ppc: Implement -dtb support for PowerNV

[Aditya Gupta <adityag@linux.ibm.com>]

Currently any device tree passed with -dtb option in QEMU, was ignored
by the PowerNV code.

Read and pass the passed -dtb to the kernel, thus enabling easier
debugging with custom DTBs.

The existing behaviour when -dtb is 'not' passed, is preserved as-is.

But when a '-dtb' is passed, it completely overrides any dtb nodes or
changes QEMU might have done, such as '-append' arguments to the kernel
(which are mentioned in /chosen/bootargs in the dtb), hence add warning
when -dtb is being used

Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>

---
Changelog
===========
v4:
 + use 'MachineState::fdt' instead of 'PnvMachineState::fdt'
 + added an 'if' check at end of pnv_reset, so we don't free the fdt we
   are using
v3:
 + use 'load_device_tree' to read the device tree, instead of g_file_get_contents
 + tested that passed dtb does NOT get ignored on system_reset

v2:
 + move reading dtb and warning to pnv_init

v1:
 + use 'g_file_get_contents' and add check for -append & -dtb as suggested by Daniel
---
---
 hw/ppc/pnv.c | 51 ++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 40 insertions(+), 11 deletions(-)

diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
index 3526852685b4..5be15f748e45 100644
--- a/hw/ppc/pnv.c
+++ b/hw/ppc/pnv.c
@@ -736,21 +736,27 @@ static void pnv_reset(MachineState *machine, ShutdownCause reason)
         }
     }
 
-    fdt = pnv_dt_create(machine);
-
-    /* Pack resulting tree */
-    _FDT((fdt_pack(fdt)));
+    if (machine->fdt) {
+        fdt = machine->fdt;
+    } else {
+        fdt = pnv_dt_create(machine);
+        /* Pack resulting tree */
+        _FDT((fdt_pack(fdt)));
+    }
 
     qemu_fdt_dumpdtb(fdt, fdt_totalsize(fdt));
     cpu_physical_memory_write(PNV_FDT_ADDR, fdt, fdt_totalsize(fdt));
 
-    /*
-     * Set machine->fdt for 'dumpdtb' QMP/HMP command. Free
-     * the existing machine->fdt to avoid leaking it during
-     * a reset.
-     */
-    g_free(machine->fdt);
-    machine->fdt = fdt;
+    /* Update machine->fdt with latest fdt */
+    if (machine->fdt != fdt) {
+        /*
+         * Set machine->fdt for 'dumpdtb' QMP/HMP command. Free
+         * the existing machine->fdt to avoid leaking it during
+         * a reset.
+         */
+        g_free(machine->fdt);
+        machine->fdt = fdt;
+    }
 }
 
 static ISABus *pnv_chip_power8_isa_create(PnvChip *chip, Error **errp)
@@ -952,6 +958,14 @@ static void pnv_init(MachineState *machine)
         g_free(sz);
         exit(EXIT_FAILURE);
     }
+
+    /* checks for invalid option combinations */
+    if (machine->dtb && (strlen(machine->kernel_cmdline) != 0)) {
+        error_report("-append and -dtb cannot be used together, as passed"
+                " command line is ignored in case of custom dtb");
+        exit(EXIT_FAILURE);
+    }
+
     memory_region_add_subregion(get_system_memory(), 0, machine->ram);
 
     /*
@@ -1003,6 +1017,21 @@ static void pnv_init(MachineState *machine)
         }
     }
 
+    /* load dtb if passed */
+    if (machine->dtb) {
+        int fdt_size;
+
+        warn_report("with manually passed dtb, some options like '-append'"
+                " will get ignored and the dtb passed will be used as-is");
+
+        /* read the file 'machine->dtb', and load it into 'fdt' buffer */
+        machine->fdt = load_device_tree(machine->dtb, &fdt_size);
+        if (!machine->fdt) {
+            error_report("Could not load dtb '%s'", machine->dtb);
+            exit(1);
+        }
+    }
+
     /* MSIs are supported on this platform */
     msi_nonbroken = true;
 
-- 
2.46.0