serial: serial_xen: Add Xen PV serial driver

Add support for Xen para-virtualized serial driver. This
driver fully supports serial console for the virtual machine.

Please note that as the driver is initialized late, so no banner
nor memory size is visible.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Anastasiia Lukianenko <anastasiia_lukianenko@epam.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/Kconfig

@@ -1755,6 +1755,7 @@ config TARGET_XENGUEST_ARM64
 	select XEN
 	select OF_CONTROL
 	select LINUX_KERNEL_IMAGE_HEADER
+	select XEN_SERIAL
 endchoice
 
 config ARCH_SUPPORT_TFABOOT

board/xen/xenguest_arm64/xenguest_arm64.c

@@ -17,9 +17,12 @@
 #include <asm/armv8/mmu.h>
 #include <asm/xen.h>
 #include <asm/xen/hypercall.h>
+#include <asm/xen/system.h>
 
 #include <linux/compiler.h>
 
+#include <xen/hvm.h>
+
 DECLARE_GLOBAL_DATA_PTR;
 
 int board_init(void)
@@ -56,9 +59,28 @@ static int get_next_memory_node(const void *blob, int mem)
 
 static int setup_mem_map(void)
 {
-	int i, ret, mem, reg = 0;
+	int i = 0, ret, mem, reg = 0;
 	struct fdt_resource res;
 	const void *blob = gd->fdt_blob;
+	u64 gfn;
+
+	/*
+	 * Add "magic" region which is used by Xen to provide some essentials
+	 * for the guest: we need console.
+	 */
+	ret = hvm_get_parameter_maintain_dcache(HVM_PARAM_CONSOLE_PFN, &gfn);
+	if (ret < 0) {
+		printf("%s: Can't get HVM_PARAM_CONSOLE_PFN, ret %d\n",
+		       __func__, ret);
+		return -EINVAL;
+	}
+
+	xen_mem_map[i].virt = PFN_PHYS(gfn);
+	xen_mem_map[i].phys = PFN_PHYS(gfn);
+	xen_mem_map[i].size = PAGE_SIZE;
+	xen_mem_map[i].attrs = (PTE_BLOCK_MEMTYPE(MT_NORMAL) |
+				PTE_BLOCK_INNER_SHARE);
+	i++;
 
 	mem = get_next_memory_node(blob, -1);
 	if (mem < 0) {
@@ -66,7 +88,7 @@ static int setup_mem_map(void)
 		return -EINVAL;
 	}
 
-	for (i = 0; i < MAX_MEM_MAP_REGIONS; i++) {
+	for (; i < MAX_MEM_MAP_REGIONS; i++) {
 		ret = fdt_get_resource(blob, mem, "reg", reg++, &res);
 		if (ret == -FDT_ERR_NOTFOUND) {
 			reg = 0;
@@ -145,8 +167,3 @@ int print_cpuinfo(void)
 	return 0;
 }
 
-__weak struct serial_device *default_serial_console(void)
-{
-	return NULL;
-}
-

configs/xenguest_arm64_defconfig

@@ -49,7 +49,7 @@ CONFIG_CMD_UMS=n
 
 CONFIG_DM=y
 # CONFIG_MMC is not set
-# CONFIG_DM_SERIAL is not set
+CONFIG_DM_SERIAL=y
 # CONFIG_REQUIRE_SERIAL_CONSOLE is not set
 
 CONFIG_OF_BOARD=y

drivers/serial/Kconfig

@@ -822,6 +822,13 @@ config MPC8XX_CONS
 	depends on MPC8xx
 	default y
 
+config XEN_SERIAL
+	bool "XEN serial support"
+	depends on XEN
+	help
+	  If built without DM support, then requires Xen
+	  to be built with CONFIG_VERBOSE_DEBUG.
+
 choice
 	prompt "Console port"
 	default 8xx_CONS_SMC1

drivers/serial/Makefile

@@ -70,6 +70,7 @@ obj-$(CONFIG_OWL_SERIAL) += serial_owl.o
 obj-$(CONFIG_OMAP_SERIAL) += serial_omap.o
 obj-$(CONFIG_MTK_SERIAL) += serial_mtk.o
 obj-$(CONFIG_SIFIVE_SERIAL) += serial_sifive.o
+obj-$(CONFIG_XEN_SERIAL) += serial_xen.o
 
 ifndef CONFIG_SPL_BUILD
 obj-$(CONFIG_USB_TTY) += usbtty.o

drivers/serial/serial_xen.c

@@ -0,0 +1,182 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * (C) 2018 NXP
+ * (C) 2020 EPAM Systems Inc.
+ */
+#include <common.h>
+#include <cpu_func.h>
+#include <dm.h>
+#include <serial.h>
+#include <watchdog.h>
+
+#include <linux/bug.h>
+
+#include <xen/hvm.h>
+#include <xen/events.h>
+
+#include <xen/interface/sched.h>
+#include <xen/interface/hvm/hvm_op.h>
+#include <xen/interface/hvm/params.h>
+#include <xen/interface/io/console.h>
+#include <xen/interface/io/ring.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+u32 console_evtchn;
+
+/*
+ * struct xen_uart_priv - Structure representing a Xen UART info
+ * @intf:    Console I/O interface for Xen guest OSes
+ * @evtchn:  Console event channel
+ */
+struct xen_uart_priv {
+	struct xencons_interface *intf;
+	u32 evtchn;
+};
+
+int xen_serial_setbrg(struct udevice *dev, int baudrate)
+{
+	return 0;
+}
+
+static int xen_serial_probe(struct udevice *dev)
+{
+	struct xen_uart_priv *priv = dev_get_priv(dev);
+	u64 val = 0;
+	unsigned long gfn;
+	int ret;
+
+	ret = hvm_get_parameter(HVM_PARAM_CONSOLE_EVTCHN, &val);
+	if (ret < 0 || val == 0)
+		return ret;
+
+	priv->evtchn = val;
+	console_evtchn = val;
+
+	ret = hvm_get_parameter(HVM_PARAM_CONSOLE_PFN, &val);
+	if (ret < 0)
+		return ret;
+
+	if (!val)
+		return -EINVAL;
+
+	gfn = val;
+	priv->intf = (struct xencons_interface *)(gfn << XEN_PAGE_SHIFT);
+
+	return 0;
+}
+
+static int xen_serial_pending(struct udevice *dev, bool input)
+{
+	struct xen_uart_priv *priv = dev_get_priv(dev);
+	struct xencons_interface *intf = priv->intf;
+
+	if (!input || intf->in_cons == intf->in_prod)
+		return 0;
+
+	return 1;
+}
+
+static int xen_serial_getc(struct udevice *dev)
+{
+	struct xen_uart_priv *priv = dev_get_priv(dev);
+	struct xencons_interface *intf = priv->intf;
+	XENCONS_RING_IDX cons;
+	char c;
+
+	while (intf->in_cons == intf->in_prod)
+		mb(); /* wait */
+
+	cons = intf->in_cons;
+	mb();			/* get pointers before reading ring */
+
+	c = intf->in[MASK_XENCONS_IDX(cons++, intf->in)];
+
+	mb();			/* read ring before consuming */
+	intf->in_cons = cons;
+
+	notify_remote_via_evtchn(priv->evtchn);
+
+	return c;
+}
+
+static int __write_console(struct udevice *dev, const char *data, int len)
+{
+	struct xen_uart_priv *priv = dev_get_priv(dev);
+	struct xencons_interface *intf = priv->intf;
+	XENCONS_RING_IDX cons, prod;
+	int sent = 0;
+
+	cons = intf->out_cons;
+	prod = intf->out_prod;
+	mb(); /* Update pointer */
+
+	WARN_ON((prod - cons) > sizeof(intf->out));
+
+	while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
+		intf->out[MASK_XENCONS_IDX(prod++, intf->out)] = data[sent++];
+
+	mb(); /* Update data before pointer */
+	intf->out_prod = prod;
+
+	if (sent)
+		notify_remote_via_evtchn(priv->evtchn);
+
+	return sent;
+}
+
+static int write_console(struct udevice *dev, const char *data, int len)
+{
+	/*
+	 * Make sure the whole buffer is emitted, polling if
+	 * necessary.  We don't ever want to rely on the hvc daemon
+	 * because the most interesting console output is when the
+	 * kernel is crippled.
+	 */
+	while (len) {
+		int sent = __write_console(dev, data, len);
+
+		data += sent;
+		len -= sent;
+
+		if (unlikely(len))
+			HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
+	}
+
+	return 0;
+}
+
+static int xen_serial_putc(struct udevice *dev, const char ch)
+{
+	write_console(dev, &ch, 1);
+
+	return 0;
+}
+
+static const struct dm_serial_ops xen_serial_ops = {
+	.putc = xen_serial_putc,
+	.getc = xen_serial_getc,
+	.pending = xen_serial_pending,
+};
+
+#if CONFIG_IS_ENABLED(OF_CONTROL)
+static const struct udevice_id xen_serial_ids[] = {
+	{ .compatible = "xen,xen" },
+	{ }
+};
+#endif
+
+U_BOOT_DRIVER(serial_xen) = {
+	.name			= "serial_xen",
+	.id			= UCLASS_SERIAL,
+#if CONFIG_IS_ENABLED(OF_CONTROL)
+	.of_match		= xen_serial_ids,
+#endif
+	.priv_auto_alloc_size	= sizeof(struct xen_uart_priv),
+	.probe			= xen_serial_probe,
+	.ops			= &xen_serial_ops,
+#if !CONFIG_IS_ENABLED(OF_CONTROL)
+	.flags			= DM_FLAG_PRE_RELOC,
+#endif
+};
+

drivers/xen/events.c

@@ -23,6 +23,8 @@
 #include <xen/events.h>
 #include <xen/hvm.h>
 
+extern u32 console_evtchn;
+
 #define NR_EVS 1024
 
 /**
@@ -49,6 +51,8 @@ void unbind_all_ports(void)
 	struct vcpu_info *vcpu_info = &s->vcpu_info[cpu];
 
 	for (i = 0; i < NR_EVS; i++) {
+		if (i == console_evtchn)
+			continue;
 		if (test_and_clear_bit(i, bound_ports)) {
 			printf("port %d still bound!\n", i);
 			unbind_evtchn(i);