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

From: Laura Abbott <labbott@redhat.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	dri-devel@lists.freedesktop.org
Cc: Sumit Semwal <sumit.semwal@linaro.org>,
	Riley Andrews <riandrews@android.com>,
	arve@android.com, devel@driverdev.osuosl.org, romlem@google.com,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
	linux-mm@kvack.org, Mark Brown <broonie@kernel.org>,
	Daniel Vetter <daniel.vetter@intel.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-media@vger.kernel.org
Subject: Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging
Date: Fri, 3 Mar 2017 11:14:47 -0800	[thread overview]
Message-ID: <a7cfd3c5-435f-3fba-33d8-69330768eb5c@redhat.com> (raw)
In-Reply-To: <1836110.VXJcCJDUAn@avalon>

On 03/03/2017 08:25 AM, Laurent Pinchart wrote:
> Hi Laura,
> 
> Thank you for the patches.
> 
> On Thursday 02 Mar 2017 13:44:32 Laura Abbott wrote:
>> Hi,
>>
>> There's been some recent discussions[1] about Ion-like frameworks. There's
>> apparently interest in just keeping Ion since it works reasonablly well.
>> This series does what should be the final clean ups for it to possibly be
>> moved out of staging.
>>
>> This includes the following:
>> - Some general clean up and removal of features that never got a lot of use
>>   as far as I can tell.
>> - Fixing up the caching. This is the series I proposed back in December[2]
>>   but never heard any feedback on. It will certainly break existing
>>   applications that rely on the implicit caching. I'd rather make an effort
>>   to move to a model that isn't going directly against the establishement
>>   though.
>> - Fixing up the platform support. The devicetree approach was never well
>>   recieved by DT maintainers. The proposal here is to think of Ion less as
>>   specifying requirements and more of a framework for exposing memory to
>>   userspace.
> 
> That's where most of my concerns with ion are. I still strongly believe that 
> the heap-based approach is inherently flawed, as it would need to be 
> configured for each device according to product-specific use cases. That's not 
> something that could be easily shipped with a generic distribution. We should 
> replace that with a constraint-based system.
> 

I don't think of constraints and heaps as being mutually exclusive. Some general
heaps (e.g. system heaps) can be available always. Others might just be
exposed if there is a particular memory region available. The constraint solving
is responsible for querying and figuring out what's the best choice.

Thanks,
Laura