[PATCH 2/4] arch: arm/xen: add putc() for debugging

[Peng Fan]

> Subject: [PATCH 2/4] 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 at linaro.org>
> ---
>  arch/arm/include/asm/xen/hypercall.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm/include/asm/xen/hypercall.h
> b/arch/arm/include/asm/xen/hypercall.h
> index a4fd077079a9..121ccfcc608f 100644
> --- 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 */

Reviewed-by: Peng Fan <peng.fan at nxp.com>

> --
> 2.28.0