[Mesa-dev] [PATCH 0/2] anv/i965: drop libdrm dependency completely

[Kristian Høgsberg]

On Thu, May 4, 2017 at 7:26 AM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
> On 27 April 2017 at 16:20, Eric Anholt <eric at anholt.net> wrote:
>> Emil Velikov <emil.l.velikov at gmail.com> writes:
>>
>>> On 25 April 2017 at 23:56, Lionel Landwerlin
>>> <lionel.g.landwerlin at intel.com> wrote:
>>>> Hi,
>>>>
>>>> While working with changes that span from kernel to user space, I've
>>>> been wondering whether we need to depend on libdrm at all for the anv
>>>> & i965 drivers. Indeed with Ken's recent changes, we only depend on
>>>> libdrm for its kernel header files which we could just embed
>>>> ourselves.
>>>>
>>>> I've only included the minimal set of header files we need from the
>>>> kernel for anv & i965. Maybe other drivers would be interested and
>>>> maybe we should put all the kernel drm uapi headers into include?
>>>>
>>> AFAICT the goal behind the libdrm_intel fold was to allow rapid and
>>> seamless rework of the interface.
>>> With a potential goal to make it a shared one, as it gets stabilised.
>>>
>>> Currently ANV uses more than just the UAPI headers. But if we ignore
>>> that, coping them is a bad idea.
>>>
>>> Why - adds a, yet another, copy and making synchronisation more
>>> annoying. First example - you blindly copied the files rather than
>>> using `make headers_install' first ;-)
>>> Not to mention that it makes the chicken and egg problem* even more
>>> confusing and error prone.
>>>
>>> Emil
>>> *  Which patches land first - kernel or userspace
>>
>> I don't see how it does that at all.  It simplifies the process: Now you
>> send out your proposed new userspace to one repo, instead of two.
>>
> Funny that you should say that. On my count there's 4 instances of the
> VC4 headers - one in kernel and 3 in different userspace components.
> With each one subtly different from the rest.

You're making this seem a lot worse than it is. It's not like these
header files are actively developed in 4 different projects. There's
exactly one canonical source for these headers with a well established
development process: the kernel. The fact that the headers are
different just means that the various userspace components have copied
the kernel headers at different times as they implemented new features
on different schedules. I'm sure you understand this.

I think it's pretty simple: requiring i965 or anv to link to libdrm
just for the ioctl wrapper and the header file which comes from the
kernel makes little sense.

Kristian

> Now consider what will happen if you throw a dozen+ developers.
>
>> And, after the first commit, it'll be obvious when you screw up using
>> make headers_install because there will be surprising diff.
>
> People rarely look at these. Bu even ignoring that for a moment:
> Developers simply don't reference (hint hint [1]) the kernel commit
> thus it's impossible to verify the patch.
>
> -Emil
> [1] See your libdrm commits 2212a6465d1597fbc4d4ee0ea5ff87816bfa336e
> and 2212a6465d1597fbc4d4ee0ea5ff87816bfa336e
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