linux-kernel - Re: [RFC][PATCH 6/6] staging: android: ion: Introduce new ioctls for dynamic heaps

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Message-ID: <20160609082502.GA31014@e106950-lin.cambridge.arm.com>
Date:	Thu, 9 Jun 2016 09:25:02 +0100
From:	Brian Starkey <brian.starkey@....com>
To:	Laura Abbott <labbott@...hat.com>
Cc:	Sumit Semwal <sumit.semwal@...aro.org>,
	John Stultz <john.stultz@...aro.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Laura Abbott <labbott@...oraproject.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linaro-mm-sig@...ts.linaro.org, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org,
	Eun Taik Lee <eun.taik.lee@...sung.com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Jon Medhurst <tixy@...aro.org>,
	Mitchel Humpherys <mitchelh@...eaurora.org>,
	Jeremy Gebben <jgebben@...eaurora.org>,
	Bryan Huntsman <bryanh@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [RFC][PATCH 6/6] staging: android: ion: Introduce new ioctls for
 dynamic heaps

Hi Laura,

On Wed, Jun 08, 2016 at 12:14:12PM -0700, Laura Abbott wrote:
>
>For now I'm just going to focus on comments not about the heap ID mapping
>because I'm leaning towards dropping the heap ID mapping.
>

Fair enough. Like you said, giving userspace enough information to just
figure out the right heap IDs is already a big improvement.

>
>I'm not that familiar with the DRM ioctls but this sounds like a
>good suggestion. One less ioctl to worry about.
>

Sorry, I probably should have pointed to an example:
http://lxr.free-electrons.com/source/drivers/gpu/drm/drm_crtc.c#L2325

>>>+ */
>>>+struct ion_heap_query {
>>>+    __u32 cnt; /* Total number of heaps to be copied */
>>>+    __u64 heaps; /* buffer to be populated */
>>
>>I guess this field needs explicit alignment to 64 bits
>>
>
>Yes, I was going by the suggestion in botching-up-ioctls.txt
>
>https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/ioctl/botching-up-ioctls.txt#n42
>

The type is fine, but you should add a 32-bit padding field before
heaps:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/ioctl/botching-up-ioctls.txt#n32

Cheers,

-Brian