On Tue, 24 Sep 2024, Edgar E. Iglesias wrote:
> From: "Edgar E. Iglesias" <edgar.iglesias@amd.com>
>
> Add a read-const writes-ignored mmio handler. This is useful
> to for example register background regions that return a fixed
> value instead of raising data aborts.
>
> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
> ---
> xen/arch/arm/include/asm/mmio.h | 2 ++
> xen/arch/arm/io.c | 21 +++++++++++++++++++++
> 2 files changed, 23 insertions(+)
>
> diff --git a/xen/arch/arm/include/asm/mmio.h b/xen/arch/arm/include/asm/mmio.h
> index 7da542cd79..605620a2f4 100644
> --- a/xen/arch/arm/include/asm/mmio.h
> +++ b/xen/arch/arm/include/asm/mmio.h
> @@ -82,6 +82,8 @@ struct vmmio {
> struct mmio_handler *handlers;
> };
>
> +extern const struct mmio_handler_ops mmio_read_const_writes_ignored;
> +
> enum io_state try_handle_mmio(struct cpu_user_regs *regs,
> mmio_info_t *info);
> void register_mmio_bg_handler(struct domain *d,
> diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
> index 934a2ad2b9..8ab0435afc 100644
> --- a/xen/arch/arm/io.c
> +++ b/xen/arch/arm/io.c
> @@ -20,6 +20,27 @@
>
> #include "decode.h"
>
> +/*
> + * Reusable mmio handler useful as background while waiting for IOREQ.
> + * Register with priv as default read value. Writes ignored.
> + */
> +static int bg_read(struct vcpu *v, mmio_info_t *info, register_t *r, void *priv)
> +{
> + *r = (uintptr_t) priv;
> + return 1;
> +}
> +
> +static int bg_write(struct vcpu *v, mmio_info_t *info, register_t r, void *priv)
> +{
> + return 1;
> +}
> +
> +/* Read const value (from priv), writes ignored. */
> +const struct mmio_handler_ops mmio_read_const_writes_ignored = {
> + .read = bg_read,
> + .write = bg_write,
> +};
> +
> static enum io_state handle_read(const struct mmio_handler *handler,
> struct vcpu *v,
> mmio_info_t *info)
> --
> 2.43.0
>