linux-kernel - Re: [Linux-graphics-maintainer] [PATCH 3/6] Input: Update vmmouse.c to use the common VMW

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Message-ID: <565F2A67.3040104@vmware.com>
Date:	Wed, 2 Dec 2015 18:29:11 +0100
From:	Thomas Hellstrom <thellstrom@...are.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Arnd Bergmann <arnd@...db.de>,
	"pv-drivers@...are.com" <pv-drivers@...are.com>,
	X86 ML <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	<virtualization@...ts.linux-foundation.org>,
	"linux-graphics-maintainer@...are.com" 
	<linux-graphics-maintainer@...are.com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>
Subject: Re: [Linux-graphics-maintainer] [PATCH 3/6] Input: Update vmmouse.c
 to use the common VMW_PORT macros

On 12/02/2015 06:26 PM, Dmitry Torokhov wrote:
> On Wed, Dec 02, 2015 at 07:31:24AM -0800, Greg Kroah-Hartman wrote:
>> On Tue, Dec 01, 2015 at 06:21:06PM -0800, Sinclair Yeh wrote:
>>> On Tue, Dec 01, 2015 at 04:04:08PM -0800, Greg Kroah-Hartman wrote:
>>>> On Tue, Dec 01, 2015 at 02:54:20PM -0800, Sinclair Yeh 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@...are.com> 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.
>>>> But the macro is only used here, and the variables aren't used at all,
>>>> so it makes no sense in this file.
>>> Maybe it's because I didn't CC you on the rest of the series.  I wasn't
>>> sure what the proper distribution list is for each part.
>> Use scripts/get_maintainer.pl, that's what it is there for.  A number of
>> those patches should go through me, if not all of them, if you want them
>> merged...
>>
>>> This new macro is also used in arch/x86/kernel/cpu/vmware.c and
>>> vmw_balloon.c
>> And it's used inconsistantly in those patches (you don't set the dummy
>> variables to 0 in all of them...)  Now maybe that's just how the asm
>> functions work, but it's not very obvious as to why this is at all.
>>
>>>>> The second reason is this organization makes some on-going future
>>>>> development easier.
>>>> We don't plan for "future" development other than a single patch series,
>>>> as we have no idea what that development is, nor if it will really
>>>> happen.  You can always change this file later if you need to, nothing
>>>> is keeping that from happening.
>>> So the intent of this series is to centralize similar lines of inline
>>> assembly code that are currently used by 3 different kernel modules
>>> to a central place.  The new vmware.h [patch 0/6] becomes the one header
>>> to include for common guest-host communication needs.
>> Why can't it go into vmw_vmci_defs.h instead, or your other .h file, why
>> create yet-another-.h-file for your bus?  You already have 2, this would
>> make it 3, which seems like a lot...
> Umm, you are not saying that vmmouse should include vmci header file(s),
> are you? Because the 2 are unrelated and vmci does not use the
> hypervisor port to communicate with host IIRC.

Also the platform setup code uses the hypervisor port, so it's a natural
place for the macro defines.

/Thomas


>
> Thanks.
>

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