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

From: Rob Clark <robdclark@gmail.com>
To: "Brian Starkey" <brian.starkey@arm.com>,
	"Laura Abbott" <labbott@redhat.com>,
	"Benjamin Gaignard" <benjamin.gaignard@linaro.org>,
	"Mark Brown" <broonie@kernel.org>,
	"Michal Hocko" <mhocko@kernel.org>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Riley Andrews" <riandrews@android.com>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Rom Lemarchand" <romlem@google.com>,
	devel@driverdev.osuosl.org,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"linaro-mm-sig@lists.linaro.org" <linaro-mm-sig@lists.linaro.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	linux-mm <linux-mm@kvack.org>
Subject: Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging
Date: Fri, 10 Mar 2017 08:56:32 -0500	[thread overview]
Message-ID: <CAF6AEGtTicaJnApMSrmdQnriQd_rwQBW4H8rH+Xe9evkwZy8eg@mail.gmail.com> (raw)
In-Reply-To: <20170310124043.45hdu64wd4acf4it@phenom.ffwll.local>

On Fri, Mar 10, 2017 at 7:40 AM, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Fri, Mar 10, 2017 at 10:31:13AM +0000, Brian Starkey wrote:
>> Hi,
>>
>> On Thu, Mar 09, 2017 at 09:38:49AM -0800, Laura Abbott wrote:
>> > On 03/09/2017 02:00 AM, Benjamin Gaignard wrote:
>>
>> [snip]
>>
>> > >
>> > > 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.
>> >
>>
>> Is the only motivation for removing the alignment parameter that
>> no-one got around to using it for something useful yet?
>> The original comment was true - different devices do have different
>> alignment requirements.
>>
>> Better alignment can help SMMUs use larger blocks when mapping,
>> reducing TLB pressure and the chance of a page table walk causing
>> display underruns.
>
> Extending ioctl uapi is easy, trying to get rid of bad uapi is much
> harder. Given that right now we don't have an ion allocator that does
> alignment I think removing it makes sense. And if we go with lots of
> heaps, we might as well have an ion heap per alignment that your hw needs,
> so there's different ways to implement this in the future.

slight correction:  if you plan ahead (and do things like zero init if
userspace passes in a smaller ioctl struct like drm_ioctl does),
extending ioctl uapi is easy.. might be something worth fixing from
the get-go..

BR,
-R

> At least from the unix device memory allocator pov it's probably simpler
> to encode stuff like this into the heap name, instead of having to pass
> heap + list of additional properties/constraints.
> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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