[REPOST PATCH 1/8] fence: dma-buf cross-device synchronization (v17)

[Rob Clark]

On Thu, Jun 19, 2014 at 5:50 PM, Dave Airlie <airlied at gmail.com> wrote:
> On 20 June 2014 04:19, Greg KH <gregkh at linuxfoundation.org> wrote:
>> On Thu, Jun 19, 2014 at 01:45:30PM -0400, Rob Clark wrote:
>>> On Thu, Jun 19, 2014 at 1:00 PM, Greg KH <gregkh at linuxfoundation.org> wrote:
>>> > On Thu, Jun 19, 2014 at 10:00:18AM -0400, Rob Clark wrote:
>>> >> On Wed, Jun 18, 2014 at 9:13 PM, Greg KH <gregkh at linuxfoundation.org> wrote:
>>> >> > On Wed, Jun 18, 2014 at 12:36:54PM +0200, Maarten Lankhorst wrote:
>>> >> >> +#define CREATE_TRACE_POINTS
>>> >> >> +#include <trace/events/fence.h>
>>> >> >> +
>>> >> >> +EXPORT_TRACEPOINT_SYMBOL(fence_annotate_wait_on);
>>> >> >> +EXPORT_TRACEPOINT_SYMBOL(fence_emit);
>>> >> >
>>> >> > Are you really willing to live with these as tracepoints for forever?
>>> >> > What is the use of them in debugging?  Was it just for debugging the
>>> >> > fence code, or for something else?
>>> >> >
>>> >> >> +/**
>>> >> >> + * fence_context_alloc - allocate an array of fence contexts
>>> >> >> + * @num:     [in]    amount of contexts to allocate
>>> >> >> + *
>>> >> >> + * This function will return the first index of the number of fences allocated.
>>> >> >> + * The fence context is used for setting fence->context to a unique number.
>>> >> >> + */
>>> >> >> +unsigned fence_context_alloc(unsigned num)
>>> >> >> +{
>>> >> >> +     BUG_ON(!num);
>>> >> >> +     return atomic_add_return(num, &fence_context_counter) - num;
>>> >> >> +}
>>> >> >> +EXPORT_SYMBOL(fence_context_alloc);
>>> >> >
>>> >> > EXPORT_SYMBOL_GPL()?  Same goes for all of the exports in here.
>>> >> > Traditionally all of the driver core exports have been with this
>>> >> > marking, any objection to making that change here as well?
>>> >>
>>> >> tbh, I prefer EXPORT_SYMBOL()..  well, I'd prefer even more if there
>>> >> wasn't even a need for EXPORT_SYMBOL_GPL(), but sadly it is a fact of
>>> >> life.  We already went through this debate once with dma-buf.  We
>>> >> aren't going to change $evil_vendor's mind about non-gpl modules.  The
>>> >> only result will be a more flugly convoluted solution (ie. use syncpt
>>> >> EXPORT_SYMBOL() on top of fence EXPORT_SYMBOL_GPL()) just as a
>>> >> workaround, with the result that no-one benefits.
>>> >
>>> > It has been proven that using _GPL() exports have caused companies to
>>> > release their code "properly" over the years, so as these really are
>>> > Linux-only apis, please change them to be marked this way, it helps
>>> > everyone out in the end.
>>>
>>> Well, maybe that is the true in some cases.  But it certainly didn't
>>> work out that way for dma-buf.  And I think the end result is worse.
>>>
>>> I don't really like coming down on the side of EXPORT_SYMBOL() instead
>>> of EXPORT_SYMBOL_GPL(), but if we do use EXPORT_SYMBOL_GPL() then the
>>> result will only be creative workarounds using the _GPL symbols
>>> indirectly by whatever is available via EXPORT_SYMBOL().  I don't
>>> really see how that will be better.
>>
>> You are saying that you _know_ companies will violate our license, so
>> you should just "give up"?  And how do you know people aren't working on
>> preventing those "indirect" usages as well?  :)
>>
>> Sorry, I'm not going to give up here, again, it has proven to work in
>> the past in changing the ways of _very_ large companies, why stop now?
>
> I've found large companies shipping lots of hw putting pressure on
> other large/small companies seems to be only way this has ever
> happened, we'd like to cover that up and say its some great GPL
> enforcement thing.
>
> To be honest, author's choice is how I'd treat this.
>
> Personally I think _GPL is broken by design, and that Linus's initial
> point for them has been so diluted by random lobby groups asking for
> every symbol to be _GPL that they are becoming effectively pointless
> now. I also dislike the fact that the lobby groups don't just bring
> violators to court. I'm also sure someone like the LF could have a
> nice income stream if Linus gave them permission to enforce his
> copyrights.
>
> But anyways, has someone checked that iOS or Windows don't have a
> fence interface? so we know that this is a Linux only interface and
> any works using it are derived? Say the nvidia driver isn't a derived
> work now, will using this interface magically translate it into a
> derived work, so we can go sue them? I don't think so.

I've no ideas about what the APIs are in windows, but windows has had
multi-gpu support for a *long* time, which implies some mechanism like
dmabuf and fence.. this isn't exactly an area where we are
trailblazing here.

BR,
-R


> But its up to Maarten and Rob, and if they say no _GPL then I don't
> think we should be overriding authors intents.
>
> Dave.