Re: [PATCH v2 3/4] m25p80: Improve command handling for unsupported commands

[Philippe Mathieu-Daudé]

On 2/6/20 7:32 PM, Guenter Roeck wrote:
> Whenever an unsupported command is encountered, the current code
> interprets each transferred byte as new command. Most of the time, those
> 'commands' are interpreted as new unknown commands. However, in rare
> cases, it may be that for example address or length information
> passed with the original command is by itself a valid command.
> If that happens, the state machine may get completely confused and,
> worst case, start writing data into the flash or even erase it.
>
> To avoid the problem, transition into STATE_READING_DATA and keep
> sending a value of 0 until the chip is deselected after encountering
> an unsupported command.
>
> Signed-off-by: Guenter Roeck <address@hidden>
> ---
> v2: Split patch into two parts; improved description.
>
>   hw/block/m25p80.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
> index 53bf63856f..8227088441 100644
> --- a/hw/block/m25p80.c
> +++ b/hw/block/m25p80.c
> @@ -1161,6 +1161,11 @@ static void decode_new_cmd(Flash *s, uint32_t value)
>           s->quad_enable = false;
>           break;
>       default:
> +        s->pos = 0;
> +        s->len = 1;
> +        s->state = STATE_READING_DATA;
> +        s->data_read_loop = true;
> +        s->data[0] = 0;

Maybe self-explicit using:

           s->data[0] = NOP;

Matter of taste probably, but I find this order easier to review:

           s->state = STATE_READING_DATA;
           s->data_read_loop = true;
           s->pos = 0;
           s->data[0] = NOP;
           s->len = 1;

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

>           qemu_log_mask(LOG_GUEST_ERROR, "M25P80: Unknown cmd %x\n", value);
>           break;
>       }