x86: qemu: fix cpu device in smp boot

Currently, when booting with more that one CPU enabled, U-Boot scans
'cpu' node in device tree and calculates CPU number. This does not scale
well as changing CPU number also requires modifying .dts and re-compiling
U-Boot.

This patch uses fw_cfg interface provided by QEMU to detect online CPU
number at runtime, and dynamically adds 'cpu' device to U-Boot's driver
model.

Signed-off-by: Miao Yan <yanmiaobest@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/mp_init.c

@@ -20,8 +20,11 @@
 #include <asm/mtrr.h>
 #include <asm/processor.h>
 #include <asm/sipi.h>
+#include <asm/fw_cfg.h>
 #include <dm/device-internal.h>
 #include <dm/uclass-internal.h>
+#include <dm/lists.h>
+#include <dm/root.h>
 #include <linux/linkage.h>
 
 DECLARE_GLOBAL_DATA_PTR;
@@ -441,6 +444,69 @@ static int init_bsp(struct udevice **devp)
 	return 0;
 }
 
+#ifdef CONFIG_QEMU
+static int qemu_cpu_fixup(void)
+{
+	int ret;
+	int cpu_num;
+	int cpu_online;
+	struct udevice *dev, *pdev;
+	struct cpu_platdata *plat;
+	char *cpu;
+
+	/* first we need to find '/cpus' */
+	for (device_find_first_child(dm_root(), &pdev);
+	     pdev;
+	     device_find_next_child(&pdev)) {
+		if (!strcmp(pdev->name, "cpus"))
+			break;
+	}
+	if (!pdev) {
+		printf("unable to find cpus device\n");
+		return -ENODEV;
+	}
+
+	/* calculate cpus that are already bound */
+	cpu_num = 0;
+	for (uclass_find_first_device(UCLASS_CPU, &dev);
+	     dev;
+	     uclass_find_next_device(&dev)) {
+		cpu_num++;
+	}
+
+	/* get actual cpu number */
+	cpu_online = qemu_fwcfg_online_cpus();
+	if (cpu_online < 0) {
+		printf("unable to get online cpu number: %d\n", cpu_online);
+		return cpu_online;
+	}
+
+	/* bind addtional cpus */
+	dev = NULL;
+	for (; cpu_num < cpu_online; cpu_num++) {
+		/*
+		 * allocate device name here as device_bind_driver() does
+		 * not copy device name, 8 bytes are enough for
+		 * sizeof("cpu@") + 3 digits cpu number + '\0'
+		 */
+		cpu = malloc(8);
+		if (!cpu) {
+			printf("unable to allocate device name\n");
+			return -ENOMEM;
+		}
+		sprintf(cpu, "cpu@%d", cpu_num);
+		ret = device_bind_driver(pdev, "cpu_qemu", cpu, &dev);
+		if (ret) {
+			printf("binding cpu@%d failed: %d\n", cpu_num, ret);
+			return ret;
+		}
+		plat = dev_get_parent_platdata(dev);
+		plat->cpu_id = cpu_num;
+	}
+	return 0;
+}
+#endif
+
 int mp_init(struct mp_params *p)
 {
 	int num_aps;
@@ -454,6 +520,12 @@ int mp_init(struct mp_params *p)
 	if (ret)
 		return ret;
 
+#ifdef CONFIG_QEMU
+	ret = qemu_cpu_fixup();
+	if (ret)
+		return ret;
+#endif
+
 	ret = init_bsp(&cpu);
 	if (ret) {
 		debug("Cannot init boot CPU: err=%d\n", ret);

arch/x86/cpu/qemu/cpu.c

@@ -13,16 +13,6 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
-int cpu_qemu_bind(struct udevice *dev)
-{
-	struct cpu_platdata *plat = dev_get_parent_platdata(dev);
-
-	plat->cpu_id = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
-				      "intel,apic-id", -1);
-
-	return 0;
-}
-
 int cpu_qemu_get_desc(struct udevice *dev, char *buf, int size)
 {
 	if (size < CPU_MAX_NAME_LEN)
@@ -52,6 +42,5 @@ U_BOOT_DRIVER(cpu_qemu_drv) = {
 	.name		= "cpu_qemu",
 	.id		= UCLASS_CPU,
 	.of_match	= cpu_qemu_ids,
-	.bind		= cpu_qemu_bind,
 	.ops		= &cpu_qemu_ops,
 };