Date:   Wed, 6 Mar 2019 15:45:40 -0600
From:   "Andrew F. Davis" <afd@...com>
To:     John Stultz <john.stultz@...aro.org>
CC:     lkml <linux-kernel@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Chenbo Feng <fengc@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH 1/5 v2] dma-buf: Add dma-buf heaps framework

On 3/6/19 1:03 PM, John Stultz wrote:
> On Wed, Mar 6, 2019 at 10:18 AM Andrew F. Davis <afd@...com> wrote:
>>
>> On 3/5/19 2:54 PM, John Stultz wrote:
>>> From: "Andrew F. Davis" <afd@...com>
>>>
>>> This framework allows a unified userspace interface for dma-buf
>>> exporters, allowing userland to allocate specific types of
>>> memory for use in dma-buf sharing.
>>>
>>> Each heap is given its own device node, which a user can
>>> allocate a dma-buf fd from using the DMA_HEAP_IOC_ALLOC.
>>>
>>> This code is an evoluiton of the Android ION implementation,
>>> and a big thanks is due to its authors/maintainers over time
>>> for their effort:
>>>   Rebecca Schultz Zavin, Colin Cross, Benjamin Gaignard,
>>>   Laura Abbott, and many other contributors!
>>>
>>> Cc: Laura Abbott <labbott@...hat.com>
>>> Cc: Benjamin Gaignard <benjamin.gaignard@...aro.org>
>>> Cc: Greg KH <gregkh@...uxfoundation.org>
>>> Cc: Sumit Semwal <sumit.semwal@...aro.org>
>>> Cc: Liam Mark <lmark@...eaurora.org>
>>> Cc: Brian Starkey <Brian.Starkey@....com>
>>> Cc: Andrew F. Davis <afd@...com>
>>> Cc: Chenbo Feng <fengc@...gle.com>
>>> Cc: Alistair Strachan <astrachan@...gle.com>
>>> Cc: dri-devel@...ts.freedesktop.org
>>> Signed-off-by: Andrew F. Davis <afd@...com>
>>> [jstultz: reworded commit message, and lots of cleanups]
>>> Signed-off-by: John Stultz <john.stultz@...aro.org>
>>> ---
>>> v2:
>>> * Folded down fixes I had previously shared in implementing
>>>   heaps
>>> * Make flags a u64 (Suggested by Laura)
>>> * Add PAGE_ALIGN() fix to the core alloc funciton
>>> * IOCTL fixups suggested by Brian
>>> * Added fixes suggested by Benjamin
>>> * Removed core stats mgmt, as that should be implemented by
>>>   per-heap code
>>> * Changed alloc to return a dma-buf fd, rather then a buffer
>>>   (as it simplifies error handling)
>>> ---
>>>  MAINTAINERS                   |  16 ++++
>>>  drivers/dma-buf/Kconfig       |   8 ++
>>>  drivers/dma-buf/Makefile      |   1 +
>>>  drivers/dma-buf/dma-heap.c    | 191 ++++++++++++++++++++++++++++++++++++++++++
>>>  include/linux/dma-heap.h      |  65 ++++++++++++++
>>>  include/uapi/linux/dma-heap.h |  52 ++++++++++++
>>>  6 files changed, 333 insertions(+)
>>>  create mode 100644 drivers/dma-buf/dma-heap.c
>>>  create mode 100644 include/linux/dma-heap.h
>>>  create mode 100644 include/uapi/linux/dma-heap.h
>>>
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index ac2e518..a661e19 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -4621,6 +4621,22 @@ F:     include/linux/*fence.h
>>>  F:   Documentation/driver-api/dma-buf.rst
>>>  T:   git git://anongit.freedesktop.org/drm/drm-misc
>>>
>>> +DMA-BUF HEAPS FRAMEWORK
>>> +M:   Laura Abbott <labbott@...hat.com>
>>> +R:   Liam Mark <lmark@...eaurora.org>
>>> +R:   Brian Starkey <Brian.Starkey@....com>
>>> +R:   "Andrew F. Davis" <afd@...com>
>>
>> Quotes not needed in maintainers file.
> 
> Whatever you say, "Andrew F. Davis", or whomever you really are! ;)
> 

 <_<
 >_>
> 
>>> +
>>> +             if (heap_allocation.fd ||
>>> +                 heap_allocation.reserved0 ||
>>> +                 heap_allocation.reserved1 ||
>>> +                 heap_allocation.reserved2) {
>>
>> Seems too many reserved, I can understand one, but if we ever needed all
>> of these we would be better off just adding another alloc ioctl.
> 
> Well, we have to have one u32 for padding. And I figured if we needed
> anything more then a u32, then we're in for 2 more.
> 
> And I think the potential of the alignment and heap-private flags, I
> worry we might want to  have something, but I guess we could just add
> a new ioctl and keep the support for the old one if folks prefer.
> 
>>> +int dma_heap_add(struct dma_heap *heap)
>>> +{
>>> +     struct device *dev_ret;
>>> +     int ret;
>>> +
>>> +     if (!heap->name || !strcmp(heap->name, "")) {
>>> +             pr_err("dma_heap: Cannot add heap without a name\n");
>>
>> As these names end up as the dev name in the file system we may want to
>> check for invalid names, there is probably a helper for that somewhere.
> 
> Hrm. I'll have to look.
> 
>>> +struct dma_heap {
>>> +     const char *name;
>>> +     struct dma_heap_ops *ops;
>>> +     unsigned int minor;
>>> +     dev_t heap_devt;
>>> +     struct cdev heap_cdev;
>>> +};
>>
>> Still not sure about this, all of the members in this struct are
>> strictly internally used by the framework. The users of this framework
>> should not have access to them and only need to deal with an opaque
>> pointer for tracking themselves (can store it in a private struct of
>> their own then container_of to get back out their struct).
>>
>> Anyway, not a big deal, and if it really bugs me enough I can always go
>> fix it later, it's all kernel internal so not a blocker here. :)
> 
> I guess I'd just move the include/linux/dma-heap.h to
> drivers/dma-buf/heaps/ and keep it localized there.
> But whichever. Feel free to also send a patch and I can fold it down.
> 

The dma-heap.h needs to stay where it is, I was thinking just move
struct dma_heap to inside drivers/dma-buf/dma-heap.c. I wouldn't worry
about changing anything right now though, I'll post a patch you can
squash in later one we confirm this whole dma-heap thing will get deemed
acceptable in the first place.

Thanks,
Andrew

> thanks
> -john
> 

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