arch: arm/xen: add putc() for debugging

This new function, xen_debug_putc(), is intended to be used to
enable CONFIG_DEBUG_UART on xen guest.

Please note that the underlying functionality in Xen is available
only when Xen is configured with !NDEBUG but is much simpler than
a generic HYPERVISOR_console_io().

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>

diff --git a/arch/arm/include/asm/xen/hypercall.h b/arch/arm/include/asm/xen/hypercall.h
index a4fd077079a9a9949a04bb1181c0250422b5e903..121ccfcc608f9eeb8cd23a51689a938e2cedc15e 100644 (file)
--- a/arch/arm/include/asm/xen/hypercall.h
+++ b/arch/arm/include/asm/xen/hypercall.h
@@ -19,4 +19,10 @@ int HYPERVISOR_sched_op(int cmd, void *arg);
 int HYPERVISOR_event_channel_op(int cmd, void *arg);
 unsigned long HYPERVISOR_hvm_op(int op, void *arg);
 int HYPERVISOR_memory_op(unsigned int cmd, void *arg);
+
+static inline void xen_debug_putc(int c)
+{
+       register int v __asm__ ("x0") = c;
+       __asm__ __volatile__("hvc 0xfffe" : "=r" (v) : "0" (v));
+}
 #endif /* _ASM_ARM_XEN_HYPERCALL_H */