On Mon, Jan 16, 2012 at 5:08 PM, Anthony Liguori <anth...@codemonkey.ws> wrote:
> On 01/16/2012 10:59 AM, Stefan Hajnoczi wrote:
>>
>> On Fri, Jan 13, 2012 at 6:32 PM, Anthony Liguori<aligu...@us.ibm.com>
>> wrote:
>>>
>>> + if (strcmp(words[0], "outb") == 0 ||
>>> + strcmp(words[0], "outw") == 0 ||
>>> + strcmp(words[0], "outl") == 0) {
>>> + uint16_t addr;
>>> + uint32_t value;
>>> +
>>> + g_assert(words[1]&& words[2]);
>>> + addr = strtol(words[1], NULL, 0);
>>> + value = strtol(words[2], NULL, 0);
>>> +
>>> + if (words[0][3] == 'b') {
>>> + cpu_outb(addr, value);
>>> + } else if (words[0][3] == 'w') {
>>> + cpu_outw(addr, value);
>>> + } else if (words[0][3] == 'l') {
>>> + cpu_outl(addr, value);
>>> + }
>>> + qtest_send_prefix(chr);
>>> + qtest_send(chr, "OK\n");
>>> + } else if (strcmp(words[0], "inb") == 0 ||
>>> + strcmp(words[0], "inw") == 0 ||
>>> + strcmp(words[0], "inl") == 0) {
>>> + uint16_t addr;
>>> + uint32_t value = -1U;
>>> +
>>> + g_assert(words[1]);
>>> + addr = strtol(words[1], NULL, 0);
>>> +
>>> + if (words[0][2] == 'b') {
>>> + value = cpu_inb(addr);
>>> + } else if (words[0][2] == 'w') {
>>> + value = cpu_inw(addr);
>>> + } else if (words[0][2] == 'l') {
>>> + value = cpu_inl(addr);
>>> + }
>>> + qtest_send_prefix(chr);
>>> + qtest_send(chr, "OK 0x%04x\n", value);
>>
>>
>> Endianness is a little weird here. memory.c will byteswap if target
>> and device endianness differ.
>>
>> Imagine the case where we're on an x86 host, running a ppc guest,
>> reading from PCI configuration space (little-endian).
>
>
> These functions expect to get host native endian. The qtest wire protocol
> is a string (which has no endianness) and converts it to host native endian.
The cpu_inl() return value is not host native endian. We perform a
byteswap if the memory region endianness is different from the target
endianness. For example, big-endian target and little-endian device
means we byteswap. Little-endian target and little-endian device
means we do not byteswap.
Running the same test binary against qemu-system-x86_64 and
qemu-system-$be_arch results in 0 and 1 byteswaps, respectively. Both
can't be right.
>> Since ppc
>> (target endian) is big-endian and the device is little-endian the
>> value read/written will be byteswapped. However, our qtest runs on
>> the host and therefore we don't want that automatic swap (or we need
>> to neutralize it by performing another byteswap on top).
>
>
> ppc wouldn't use outb/inb. It would do mmio to the PIO region which would
> send it through the host controller (which would do byte swapping as
> necessary).
>
> So a qtest test case would have to do little endian MMIO to interact with
> the PCI bus.
Maybe ppc is a bad example, but are there other targets where in/out is used?
Stefan
