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

[Brian Starkey]

On Tue, Sep 06, 2016 at 03:16:52PM -0700, Laura Abbott wrote:
> 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

You can add me to that group :-)

> > 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.

If you nuke type-as-ID in dummy, and put a clear comment on the
ion_heap_type enum stating that heap-type and heap-ID are strictly
different, then I'm happy.
I think without that there'll still be confusion.

Thanks!
Brian

> > Cheers,
> > Brian
> >
> > > > Thanks,
> > > > Brian
> > > >
> > > > > Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> > > > > ---
> > > > > 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