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Date:   Thu, 28 Apr 2022 20:55:51 +0900
From:   Stafford Horne <shorne@gmail.com>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     openrisc@lists.librecores.org, linux-kernel@vger.kernel.org,
        Peter Maydell <peter.maydell@linaro.org>
Subject: Re: [PATCH] openrisc: define nop command for simulator reboot
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References: <20220428111139.1330966-1-Jason@zx2c4.com>
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On Thu, Apr 28, 2022 at 01:11:39PM +0200, Jason A. Donenfeld wrote:
> The simulator defines `l.nop 1` for shutdown, but doesn't have anything
> for reboot. Use 13 for this, which is currently unused, dubbed
> `NOP_REBOOT`.
> 
> Cc: Stafford Horne <shorne@gmail.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Link: https://lore.kernel.org/all/YmnaDUpVI5ihgvg6@zx2c4.com/
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  arch/openrisc/kernel/process.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/openrisc/kernel/process.c b/arch/openrisc/kernel/process.c
> index 3c0c91bcdcba..4cce95fa6eb5 100644
> --- a/arch/openrisc/kernel/process.c
> +++ b/arch/openrisc/kernel/process.c
> @@ -52,6 +52,8 @@ void machine_restart(char *cmd)
>  {
>  	do_kernel_restart(cmd);
>  
> +	__asm__("l.nop 13");
> +
>  	/* Give a grace period for failure to restart of 1s */
>  	mdelay(1000);
>  
> -- 
> 2.35.1

This seems fair, probably it would be good to have a comment mentioninmg what
the nop is for, fyi for context these are the nop numbers used to control
simulations.

    #define NOP_NOP          0x0000      /* Normal nop instruction */
    #define NOP_EXIT         0x0001      /* End of simulation */
    #define NOP_REPORT       0x0002      /* Simple report */
    /*#define NOP_PRINTF       0x0003       Simprintf instruction (obsolete)*/
    #define NOP_PUTC         0x0004      /* JPB: Simputc instruction */
    #define NOP_CNT_RESET    0x0005      /* Reset statistics counters */
    #define NOP_GET_TICKS    0x0006      /* JPB: Get # ticks running */
    #define NOP_GET_PS       0x0007      /* JPB: Get picosecs/cycle */
    #define NOP_TRACE_ON     0x0008      /* Turn on tracing */
    #define NOP_TRACE_OFF    0x0009      /* Turn off tracing */
    #define NOP_RANDOM       0x000a      /* Return 4 random bytes */
    #define NOP_OR1KSIM      0x000b      /* Return non-zero if this is Or1ksim */
    #define NOP_EXIT_SILENT  0x000c      /* End of simulation, quiet version */
    /* New! */
    #define NOP_RESET        0x000d      /* Reset the cpu */

I will queue this once we update the spec to define some of these, I am thinking
if qemu should allow for the shutdown to work in user mode.

BTW, are you working specifically on openrisc? Or just setting up test
environments for all architectures?

Acked-by: Stafford Horne <shorne@gmail.com>