On Tue, Dec 1, 2015 at 2:54 PM, Sinclair Yeh <syeh@xxxxxxxxxx> wrote:
> Hi,
>
> On Tue, Dec 01, 2015 at 02:45:27PM -0800, Dmitry Torokhov wrote:
>> On Tue, Dec 1, 2015 at 2:32 PM, Sinclair Yeh <syeh@xxxxxxxxxx> wrote:
>> > Hi,
>> >
>
> <snip>
>
>> >> > */
>> >> > -#define VMMOUSE_CMD(cmd, in1, out1, out2, out3, out4) \
>> >> > -({ \
>> >> > - unsigned long __dummy1, __dummy2; \
>> >> > - __asm__ __volatile__ ("inl %%dx" : \
>> >> > - "=a"(out1), \
>> >> > - "=b"(out2), \
>> >> > - "=c"(out3), \
>> >> > - "=d"(out4), \
>> >> > - "=S"(__dummy1), \
>> >> > - "=D"(__dummy2) : \
>> >> > - "a"(VMMOUSE_PROTO_MAGIC), \
>> >> > - "b"(in1), \
>> >> > - "c"(VMMOUSE_PROTO_CMD_##cmd), \
>> >> > - "d"(VMMOUSE_PROTO_PORT) : \
>> >> > - "memory"); \
>> >> > +#define VMMOUSE_CMD(cmd, in1, out1, out2, out3, out4) \
>> >> > +({ \
>> >> > + unsigned long __dummy1 = 0, __dummy2 = 0; \
>> >>
>> >> Why do we need to initialize dummies?
>> >
>> > Because for some commands those parameters to VMW_PORT() can be both
>> > input and outout.
>>
>> The vmmouse commands do not use them as input though, so it seems we
>> are simply wasting CPU cycles setting them to 0 just because we are
>> using the new VMW_PORT here. Why do we need to switch? What is the
>> benefit of doing this?
>
> There are two reasons. One is to make the code more readable and
> maintainable. Rather than having mostly similar inline assembly
> code sprinkled across multiple modules, we can just use the macros
> and document that.
At the cost of wasting cycles though :(.
Oh well, it is not like we are polling the backdoor here, so if you do
not care about a few wasted cycles I don't have to either ;)
>
> The second reason is this organization makes some on-going future
> development easier.
>
> Hope this helps.
>
> Sinclair
--
Dmitry
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