Re: [PATCH] drm/prime: remove cargo-cult locking from map_sg helper

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Wed, Jul 10, 2013 at 5:18 PM, Konrad Rzeszutek Wilk
<konrad.wilk@oracle.com> wrote:
>> So after a bit of irc chatting with Maarten this seems to be more
>> involved. The above check is to cache the dma mapping, but the
>> implementation is bogus in tons of ways:
>> - If direction changes we don't bother with unmaping and freeing the
>> mapping, but simply leak it.
>> - This will break if the dma mapping needs explicit syncing since the
>> helpers don't call sync_to_cpu/sync_to_device anywhere.
>
> Right, and I believe I signed up for that.

Well, the breakage runs deeper since atm ttm doesn't have any concept
of syncing from/to the device dma. Neither has i915. So this little
issue here is just the tip of the iceberg ...

>> So I think I'll decline to poke around more in this hornet nest and
>> leave it at the locking removal.
>
> .. and I get the hornet nest :-). Is there a IRC log of what you guys talked
> about so I don't omit certain pieces of code.

The above is pretty much the summary, actually more lines than what
we've discussed on irc ;-) It's on #dri-devel though:
http://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&show_html=true&highlight_names=&date=2013-07-10
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch