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Re: [Qemu-devel] [PATCHv2] esp: Do not overwrite ESP_TCHI after reset
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCHv2] esp: Do not overwrite ESP_TCHI after reset |
Date: |
Mon, 10 Nov 2014 19:32:19 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 |
On 10/11/2014 16:52, Hannes Reinecke wrote:
> After a reset ESP_TCHI should contain the unique ID
> of the chip. This value will be overwritten with the
> current tranfer count if the transfer count has
> previously been set.
> So we should always return the chip id if ESP_TCHI
> has never been written to.
What if ESP_TCHI was written 0? Why should it return the chip id?
Can you explain exactly what sequence of register reads/writes leads to
the bug?
Paolo
> Signed-off-by: Hannes Reinecke <address@hidden>
> ---
> hw/scsi/esp.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index 5ab44d8..2caac1c 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -364,7 +364,6 @@ void esp_hard_reset(ESPState *s)
> {
> memset(s->rregs, 0, ESP_REGS);
> memset(s->wregs, 0, ESP_REGS);
> - s->rregs[ESP_TCHI] = s->chip_id;
> s->ti_size = 0;
> s->ti_rptr = 0;
> s->ti_wptr = 0;
> @@ -422,6 +421,11 @@ uint64_t esp_reg_read(ESPState *s, uint32_t saddr)
> esp_lower_irq(s);
>
> return old_val;
> + case ESP_TCHI:
> + /* Return the unique id if the value has never been written */
> + if (!s->wregs[ESP_TCHI]) {
> + return s->chip_id;
> + }
> default:
> break;
> }
>