Re: [PATCHv2 1/4] staging: android: ion: Drop heap type masks

[Laura Abbott <labbott@redhat.com>]

On 09/05/2016 04:20 AM, Brian Starkey wrote:
> Hi,
>
> On Fri, Sep 02, 2016 at 12:36:25PM -0700, Laura Abbott wrote:
>> On 09/02/2016 06:41 AM, Brian Starkey wrote:
>>> Hi Laura,
>>>
>>> On Thu, Sep 01, 2016 at 03:40:41PM -0700, Laura Abbott wrote:
>>>>
>>>> There is no advantage to having heap types be a mask. The ion client has
>>>> long since dropped the mask. Drop the notion of heap type masks as well.
>>>>
>>>
>>> I know this is the same patch you sent last time, so sorry for not
>>> picking this up then - but I'm curious what "The" ion client is here?
>>>
>>
>> ion_client_create used to take a mask to indicate what heap types it
>> could allocate from. This hasn't been the case since 2bb9f5034ec7
>> ("gpu: ion: Remove heapmask from client"). "The ion client" probably
>> should have been "struct ion_client"
>
> Ah I see, the in-kernel ion_client. Sorry, I completely forgot that
> even existed (because it's totally useless - how is a driver meant to
> find the global ion_device?)
>
>>
>>> Our ion client(s) certainly still use these masks, and it's still
>>> used as a mask within ion itself - even if the relationship between a
>>> mask and a heap type has been somewhat lost.
>>
>> Where is it used in Ion? I don't see it in tree unless I missed something
>> and I'm not eager to keep this around for out of tree code. What's the
>> actual use for this?
>
> You're certainly right that these heap-ID-to-allocation-mask macros
> are unused in the kernel, but I don't really see the reason for
> removing them - they are convenient (for now).
>
> Example: I'm using the dummy ion driver, and I want to allocate from
> the SYSTEM_CONTIG heap - the ION_HEAP_SYSTEM_CONTIG_MASK gives me the
> exact mask I need for that.
>
> It seems your opinion is that heap-IDs are already, and should be,
> completely decoupled from their type. That sounds like a good idea to
> me, but it's not true (yet) - again check out the dummy driver.
>

Good point, I need to clean up the dummy driver to stop using heap
types as the id ;)

I get that it's convenient but it's a bad practice to conflate the
namespaces.

> At the moment, heap-IDs are assigned by ion drivers in any way they
> see fit. For as long as that stays the case there's always going to
> be heap-masks hard-coded in UAPI kernel headers (in-tree or not), so
> removing these particular masks seems a bit fruitless.
>

It's not fruitless, the concept of type as mask makes no sense. They
are two different name spaces and I've found Ion users have a hard
time keeping them separate and pass in the heap type mask when using
non dummy

> I'd rather see driver-assigned heap-IDs disappear completely, and have
> them assigned by ion core from an idr or something. At that point
> these macros really *are* meaningless, and I'd be totally fine with
> removing them (and userspace won't be able to depend on hard-coded
> allocation masks any more - it will have to use the query ioctl,
> which I assume is the whole point?).
>

Ideally yes we'd be able to get rid of the hard coded device IDs.
I consider the query ioctl a stepping stone to that, depending on
how enthusiastic people are about Ion.

> IMO it's not the right time to remove these macros, because they still
> have meaning and usefulness.
>

I still think they should be deleted to avoid namespace polution.

> Cheers,
> Brian
>
>>
>>>
>>> Thanks,
>>> Brian
>>>
>>>> Signed-off-by: Laura Abbott <labbott@redhat.com>
>>>> ---
>>>> drivers/staging/android/uapi/ion.h | 6 ------
>>>> 1 file changed, 6 deletions(-)
>>>>
>>>> diff --git a/drivers/staging/android/uapi/ion.h b/drivers/staging/android/uapi/ion.h
>>>> index 0a8e40f..a9c4e8b 100644
>>>> --- a/drivers/staging/android/uapi/ion.h
>>>> +++ b/drivers/staging/android/uapi/ion.h
>>>> @@ -44,14 +44,8 @@ enum ion_heap_type {
>>>>                   * must be last so device specific heaps always
>>>>                   * are at the end of this enum
>>>>                   */
>>>> -    ION_NUM_HEAPS = 16,
>>>> };
>>>>
>>>> -#define ION_HEAP_SYSTEM_MASK        (1 << ION_HEAP_TYPE_SYSTEM)
>>>> -#define ION_HEAP_SYSTEM_CONTIG_MASK    (1 << ION_HEAP_TYPE_SYSTEM_CONTIG)
>>>> -#define ION_HEAP_CARVEOUT_MASK        (1 << ION_HEAP_TYPE_CARVEOUT)
>>>> -#define ION_HEAP_TYPE_DMA_MASK        (1 << ION_HEAP_TYPE_DMA)
>>>> -
>>>> #define ION_NUM_HEAP_IDS        (sizeof(unsigned int) * 8)
>>>>
>>>> /**
>>>> --
>>>> 2.7.4
>>>>
>>