Re: [Qemu-devel] [PATCH for-1.4] libi2c-omap: Fix endianness dependency

[Blue Swirl]

On Sat, Feb 2, 2013 at 5:44 PM, Peter Maydell <address@hidden> wrote:
> On 2 February 2013 17:37, Andreas Färber <address@hidden> wrote:
>> Am 02.02.2013 17:49, schrieb Peter Maydell:
>>> There's nothing special about the OMAP i2c device that I know of:
>>> shouldn't the test code just be using a generic "write 16 bit value
>>> to memory with appropriate endianness for target CPU" function ?
>>
>> I asked about where to address this issue [1], no concrete answers, and
>> this is the only solution I came up with.
>>
>> libqtest.h has no generic endian-aware memread functions unlike Alex,
>> you or me expected. It reads a sequence of bytes from guest memory and
>> transmits them one-by-one over the text-based qtest protocol.
>
> OK, so this is just busted for accessing devices. The protocol
> has to have some way of letting you do a 32 bit / 16 bit / 8 bit
> access (and maybe 64 bit as well while we're here). memread
> and memwrite are OK for RAM accesses [ie anything you'd be
> happy to have cached or buffered in a real system] but for
> memory mapped registers we need to have an equivalent of
> inb/inw/inl/outb/outw/outl that guarantee to do exactly one
> access of exactly the required width.

I was also just making a patch (but not so nice as Andreas'). My
analysis was that qtest.c and libqtest.c just pass the result of
cpu_physical_memory_rw() as is, with no endian conversion. So the
result needs to be converted to host CPU order just like Andreas did.
I think the protocol is OK, my initial reaction was to put byte
swapping there but that's not right.

>
> (If you want to do a workaround for 1.4 to get the test suite
> running again I don't object; this is just a discussion about
> what the right long term fix should be.)
>
> -- PMM