On Mon, Jun 16, 2014 at 11:29:38PM +0100, Abhimanyu Kapur wrote:
> Add support for debug communications channel based
> hvc console for arm64 cpus.
Should we be setting MDSCR_EL1.TDCC to prevent userspace access to the DCC?
> Signed-off-by: Abhimanyu Kapur <abhim...@codeaurora.org>
> ---
> arch/arm64/include/asm/dcc.h | 41 +++++++++++++++++++++++++++++++++++++++++
> drivers/tty/hvc/Kconfig | 2 +-
> 2 files changed, 42 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/include/asm/dcc.h
>
> diff --git a/arch/arm64/include/asm/dcc.h b/arch/arm64/include/asm/dcc.h
> new file mode 100644
> index 0000000..ef74324
> --- /dev/null
> +++ b/arch/arm64/include/asm/dcc.h
> @@ -0,0 +1,41 @@
> +/* Copyright (c) 2014 The Linux Foundation. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 and
> + * only version 2 as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <asm/barrier.h>
> +
> +static inline u32 __dcc_getstatus(void)
> +{
> + u32 __ret;
Can this result in the mrs receiving a W register?
> + asm volatile("mrs %0, mdccsr_el0" : "=r" (__ret)
> + : : "cc");
Why the CC clobber? Why volatile?
> +
> + return __ret;
> +}
> +
> +static inline char __dcc_getchar(void)
> +{
> + char __c;
> +
> + asm volatile("mrs %0, dbgdtrrx_el0" : "=r" (__c));
> + isb();
Why the isb and why volatile??
> +
> + return __c;
> +}
> +
> +static inline void __dcc_putchar(char c)
> +{
> + asm volatile("msr dbgdtrtx_el0, %0"
> + : /* No output register */
> + : "r" (c));
Can you guarantee that GCC hasn't put junk in the upper bits of c?
> + isb();
Why the isb?
Will
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
