Re: [PATCH] hw/ide: Remove status register read side effect

[Mark Cave-Ayland]

On 21/02/2020 06:50, address@hidden wrote:

> The Linux libATA API documentation mentions that on some hardware,
> reading the status register has the side effect of clearing the
> interrupt condition. When emulating the generic Sun4u machine running
> Solaris 10, the Solaris 10 CMD646 driver exits fatally because of this
> emulated side effect. This side effect is likely to not exist on real
> CMD646 hardware.
> 
> Signed-off-by: Jasper Lowell <address@hidden>
> ---
>  hw/ide/core.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index 80000eb766..82fd0632ac 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -2210,7 +2210,6 @@ uint32_t ide_ioport_read(void *opaque, uint32_t addr)
>          } else {
>              ret = s->status;
>          }
> -        qemu_irq_lower(bus->irq);
>          break;
>      }

I don't think that this is correct: from memory when I last looked at this, 
there
were 2 IDE status registers: the one from the original specification which 
clears the
IRQ upon read, and another one in subsequent revisions which allows you to read 
the
value without clearing any pending IRQ. My guess would be that changing this 
would
not only cause QEMU to deviate from the specification, but causes problems in 
other OSs.


ATB,

Mark.