Date:   Tue, 14 Mar 2017 15:47:54 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Mark Brown <broonie@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Riley Andrews <riandrews@...roid.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        Rom Lemarchand <romlem@...gle.com>, devel@...verdev.osuosl.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Brian Starkey <brian.starkey@....com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging

2017-03-13 22:09 GMT+01:00 Laura Abbott <labbott@...hat.com>:
> On 03/12/2017 12:05 PM, Daniel Vetter wrote:
>> On Sun, Mar 12, 2017 at 2:34 PM, Benjamin Gaignard
>> <benjamin.gaignard@...aro.org> wrote:
>>> 2017-03-09 18:38 GMT+01:00 Laura Abbott <labbott@...hat.com>:
>>>> On 03/09/2017 02:00 AM, Benjamin Gaignard wrote:
>>>>> 2017-03-06 17:04 GMT+01:00 Daniel Vetter <daniel@...ll.ch>:
>>>>>> 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_$heapname nodes? Should we do this from the start, since
>> we're massively revamping the uapi anyway (imo not needed, current
>> state seems to work too)?
>> -Daniel
>>
>
> I thought about that. One advantage with separate /dev/ion_$heap

Should we use /devi/ion/$heap instead of /dev/ion_$heap ?
I think it would be easier for user to look into one directory rather
then in whole /dev to find the heaps

> is that we don't have to worry about a limit of 32 possible
> heaps per system (32-bit heap id allocation field). But dealing
> with an ioctl seems easier than names. Userspace might be less
> likely to hardcode random id numbers vs. names as well.

In the futur I think that heap type will be replaced by a "get caps"
ioctl which will
describe heap capabilities. At least that is my understanding of kernel part
of "unix memory allocator" project

>
> Thanks,
> Laura

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