Re: [Qemu-devel] [PATCH] Enable 8-byte wide MMIO for 16550 serial devices

[Paolo Bonzini <pbonzini@redhat.com>]

----- Original Message -----
> From: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
> To: "Paolo Bonzini" <pbonzini@redhat.com>, "Mike Nawrocki" <michael.nawrocki@gtri.gatech.edu>, "Avi Kivity"
> <avi@redhat.com>, "Peter Maydell" <peter.maydell@linaro.org>, "Konrad Frederic" <fred.konrad@greensocs.com>
> Cc: qemu-devel@nongnu.org, mst@redhat.com
> Sent: Thursday, November 2, 2017 8:28:09 PM
> Subject: Re: [Qemu-devel] [PATCH] Enable 8-byte wide MMIO for 16550 serial devices
> 
> Hi Mike, Paolo.
> 
> >> diff --git a/hw/char/serial.c b/hw/char/serial.c
> >> index 376bd2f240..c16c19a406 100644
> >> --- a/hw/char/serial.c
> >> +++ b/hw/char/serial.c
> >> @@ -1005,7 +1005,7 @@ static void serial_mm_write(void *opaque, hwaddr
> >> addr,
> >>                              uint64_t value, unsigned size)
> >>  {
> >>      SerialState *s = opaque;
> >> -    value &= ~0u >> (32 - (size * 8));
> >> +    value &= ~((uint64_t)0) >> (64 - (size * 8));
> >>      serial_ioport_write(s, addr >> s->it_shift, value, 1);
> >>  }
> > 
> > Couldn't this be simply "value &= 255"?  Otherwise looks good.
> 
> This is not incorrect, but I don't think this is the correct fix.
> Isn't it what memory::access_with_adjusted_size() is supposed to do with
> .impl.max_access_size = 1?

The mm version doesn't have .impl.max_access_size=1.

Thanks,

Paolo

> This looks like the same issue I tried to fix here:
> http://lists.nongnu.org/archive/html/qemu-devel/2017-08/msg02255.html
> 
> I'll try to find some time to respin the full series with tests.
> 
> >> @@ -1014,16 +1014,22 @@ static const MemoryRegionOps serial_mm_ops[3] = {
> >>          .read = serial_mm_read,
> >>          .write = serial_mm_write,
> >>          .endianness = DEVICE_NATIVE_ENDIAN,
> >> +        .valid.max_access_size = 8,
> >> +        .impl.max_access_size = 8,
> >>      },
> >>      [DEVICE_LITTLE_ENDIAN] = {
> >>          .read = serial_mm_read,
> >>          .write = serial_mm_write,
> >>          .endianness = DEVICE_LITTLE_ENDIAN,
> >> +        .valid.max_access_size = 8,
> >> +        .impl.max_access_size = 8,
> >>      },
> >>      [DEVICE_BIG_ENDIAN] = {
> >>          .read = serial_mm_read,
> >>          .write = serial_mm_write,
> >>          .endianness = DEVICE_BIG_ENDIAN,
> >> +        .valid.max_access_size = 8,
> >> +        .impl.max_access_size = 8,
>