[PATCH] xen/arm: Make hwdom vUART optional feature

[Michal Orzel <michal.orzel@xxxxxxx>]

At the moment, the hardware domain vUART is always compiled in. In the
spirit of fine granular configuration, make it optional so that the
feature can be disabled if not needed. This UART is not exposed (e.g.
via device tree) to a domain and is mostly used to support special use
cases like Linux early printk, prints from the decompressor code, etc.

Introduce Kconfig option CONFIG_HWDOM_VUART, enabled by default (to keep
the current behavior) and use it to protect the vUART related code.
Provide stubs for domain_vuart_{init,free}() in case the feature is
disabled. Take the opportunity to add a struct domain forward declaration
to vuart.h, so that the header is self contained.

Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
 xen/arch/arm/Kconfig              |  8 ++++++++
 xen/arch/arm/Makefile             |  2 +-
 xen/arch/arm/include/asm/domain.h |  2 ++
 xen/arch/arm/vuart.h              | 15 +++++++++++++++
 4 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index 50e9bfae1ac8..72af329564b7 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -150,6 +150,14 @@ config SBSA_VUART_CONSOLE
          Allows a guest to use SBSA Generic UART as a console. The
          SBSA Generic UART implements a subset of ARM PL011 UART.
 
+config HWDOM_VUART
+       bool "Emulated UART for hardware domain"
+       default y
+       help
+         Allows a hardware domain to use a minimalistic UART (single transmit
+         and status register) which takes information from dtuart. Note that 
this
+         UART is not intended to be exposed (e.g. via device-tree) to a domain.
+
 config ARM_SSBD
        bool "Speculative Store Bypass Disable" if EXPERT
        depends on HAS_ALTERNATIVE
diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
index 33c677672fe6..7b1350e2ef0a 100644
--- a/xen/arch/arm/Makefile
+++ b/xen/arch/arm/Makefile
@@ -71,7 +71,7 @@ obj-y += vtimer.o
 obj-$(CONFIG_SBSA_VUART_CONSOLE) += vpl011.o
 obj-y += vsmc.o
 obj-y += vpsci.o
-obj-y += vuart.o
+obj-$(CONFIG_HWDOM_VUART) += vuart.o
 
 extra-y += xen.lds
 
diff --git a/xen/arch/arm/include/asm/domain.h 
b/xen/arch/arm/include/asm/domain.h
index 5fb8cd79c01a..8218afb8626a 100644
--- a/xen/arch/arm/include/asm/domain.h
+++ b/xen/arch/arm/include/asm/domain.h
@@ -91,6 +91,7 @@ struct arch_domain
 
     struct vgic_dist vgic;
 
+#ifdef CONFIG_HWDOM_VUART
     struct vuart {
 #define VUART_BUF_SIZE 128
         char                        *buf;
@@ -98,6 +99,7 @@ struct arch_domain
         const struct vuart_info     *info;
         spinlock_t                  lock;
     } vuart;
+#endif
 
     unsigned int evtchn_irq;
 #ifdef CONFIG_ACPI
diff --git a/xen/arch/arm/vuart.h b/xen/arch/arm/vuart.h
index bd23bd92f631..36658b4a8c7f 100644
--- a/xen/arch/arm/vuart.h
+++ b/xen/arch/arm/vuart.h
@@ -20,9 +20,24 @@
 #ifndef __ARCH_ARM_VUART_H__
 #define __ARCH_ARM_VUART_H__
 
+struct domain;
+
+#ifdef CONFIG_HWDOM_VUART
+
 int domain_vuart_init(struct domain *d);
 void domain_vuart_free(struct domain *d);
 
+#else
+
+static inline int domain_vuart_init(struct domain *d)
+{
+    return 0;
+}
+
+static inline void domain_vuart_free(struct domain *d) {};
+
+#endif /* CONFIG_HWDOM_VUART */
+
 #endif /* __ARCH_ARM_VUART_H__ */
 
 /*
-- 
2.25.1