Re: [PATCH] Allow acpi-tmr size=2

[Michael Tokarev]

13.07.2020 10:20, Michael Tokarev пишет:
> 12.07.2020 15:00, Simon John wrote:
>> macos guests no longer boot after commit 
>> 5d971f9e672507210e77d020d89e0e89165c8fc9
>>
>> acpi-tmr needs 2 byte memory accesses, so breaks as that commit only allows 
>> 4 bytes.
>>
>> Fixes: 5d971f9e672507210e7 (memory: Revert "memory: accept mismatching sizes 
>> in memory_region_access_valid")
>> Buglink: https://bugs.launchpad.net/qemu/+bug/1886318
> 
> Actually this fixes 77d58b1e47c8d1c661f98f12b47ab519d3561488
> Author: Gerd Hoffmann <kraxel@redhat.com>
> Date:   Thu Nov 22 12:12:30 2012 +0100
> Subject: apci: switch timer to memory api
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> 
> because this is the commit which put min_access_size = 4 in there
> (5d971f9e672507210e7 is just a messenger, actual error were here
> earlier but it went unnoticed).
> 
> While min_access_size=4 was most likely an error, I wonder why
> we use 1 now, while the subject says it needs 2? What real min
> size is here for ACPI PM timer?

Actually it is more twisted than that. We can't just change the size,
we must update the corresponding code too.


static uint64_t acpi_pm_tmr_read(void *opaque, hwaddr addr, unsigned width)
{
    return acpi_pm_tmr_get(opaque);
}

note the actual read function does not even know neither the requested
address nor the requested width, it assumes the min/max constraints
are enforced and the read goes to all 4 bytes. If this pm timer can
be read byte-by-byte, we should return the right byte of the value,
not always the whole value.

/mjt