Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging

From: Daniel Vetter
Date: Sun Mar 12 2017 - 15:05:46 EST

On Sun, Mar 12, 2017 at 2:34 PM, Benjamin Gaignard
<benjamin.gaignard@xxxxxxxxxx> wrote:
> 2017-03-09 18:38 GMT+01:00 Laura Abbott <labbott@xxxxxxxxxx>:
>> On 03/09/2017 02:00 AM, Benjamin Gaignard wrote:
>>> 2017-03-06 17:04 GMT+01:00 Daniel Vetter <daniel@xxxxxxxx>:
>>>> On Mon, Mar 06, 2017 at 11:58:05AM +0100, Mark Brown wrote:
>>>>> On Mon, Mar 06, 2017 at 11:40:41AM +0100, Daniel Vetter wrote:
>>>>>> No one gave a thing about android in upstream, so Greg KH just dumped it
>>>>>> all into staging/android/. We've discussed ION a bunch of times, recorded
>>>>>> anything we'd like to fix in staging/android/TODO, and Laura's patch
>>>>>> series here addresses a big chunk of that.
>>>>>> This is pretty much the same approach we (gpu folks) used to de-stage the
>>>>>> syncpt stuff.
>>>>> Well, there's also the fact that quite a few people have issues with the
>>>>> design (like Laurent). It seems like a lot of them have either got more
>>>>> comfortable with it over time, or at least not managed to come up with
>>>>> any better ideas in the meantime.
>>>> See the TODO, it has everything a really big group (look at the patch for
>>>> the full Cc: list) figured needs to be improved at LPC 2015. We don't just
>>>> merge stuff because merging stuff is fun :-)
>>>> Laurent was even in that group ...
>>>> -Daniel
>>> For me those patches are going in the right direction.
>>> I still have few questions:
>>> - since alignment management has been remove from ion-core, should it
>>> be also removed from ioctl structure ?
>> Yes, I think I'm going to go with the suggestion to fixup the ABI
>> so we don't need the compat layer and as part of that I'm also
>> dropping the align argument.
>>> - can you we ride off ion_handle (at least in userland) and only
>>> export a dma-buf descriptor ?
>> Yes, I think this is the right direction given we're breaking
>> everything anyway. I was debating trying to keep the two but
>> moving to only dma bufs is probably cleaner. The only reason
>> I could see for keeping the handles is running out of file
>> descriptors for dma-bufs but that seems unlikely.
>>> In the future how can we add new heaps ?
>>> Some platforms have very specific memory allocation
>>> requirements (just have a look in the number of gem custom allocator in drm)
>>> Do you plan to add heap type/mask for each ?
>> Yes, that was my thinking.
> My concern is about the policy to adding heaps, will you accept
> "customs" heap per
> platforms ? per devices ? or only generic ones ?
> If you are too strict, we will have lot of out-of-tree heaps and if
> you accept of of them
> it will be a nightmare to maintain....

I think ion should expose any heap that's also directly accessible to
devices using dma_alloc(_coherent). That should leave very few things
left, like your SMA heap.

> Another point is how can we put secure rules (like selinux policy) on
> heaps since all the allocations
> go to the same device (/dev/ion) ? For example, until now, in Android
> we have to give the same
> access rights to all the process that use ION.
> It will become problem when we will add secure heaps because we won't
> be able to distinguish secure
> processes to standard ones or set specific policy per heaps.
> Maybe I'm wrong here but I have never see selinux policy checking an
> ioctl field but if that
> exist it could be a solution.

Hm, we might want to expose all the heaps as individual
/dev/ion_$heapname nodes? Should we do this from the start, since
we're massively revamping the uapi anyway (imo not needed, current
state seems to work too)?
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 -