[RFC][PATCH 1/2] WIP: Devicetree bindings for Ion

[andrew at ncrmnt.org]

20 октября 2015 г., 19:34, "Mitchel Humpherys" <mitchelh at codeaurora.org> написал:
> On Tue, Oct 13 2015 at 11:14:23 AM, Andrew <andrew at ncrmnt.org> wrote:
> 
>> On 2015-10-12 21:39, Mitchel Humpherys wrote:
>>> On Tue, Oct 06 2015 at 05:35:41 PM, Rob Herring <robherring2 at gmail.com>
>>> wrote:
>>>> On Tue, Oct 6, 2015 at 3:47 PM, Laura Abbott <labbott at fedoraproject.org>
>>>> wrote:
>>> 
>>> [...]
>>> 
>>>>> +Example:
>>>>> +
>>>>> + ion {
>>>>> + compatbile = "linux,ion";
>>>>> + #address-cells = <1>;
>>>>> + #size-cells = <0>;
>>>>> +
>>>>> + ion-system-heap {
>>>>> + linux,ion-heap-id = <0>;
>>>>> + linux,ion-heap-type = <ION_SYSTEM_HEAP_TYPE>;
>>>>> + linux,ion-heap-name = "system";
>>>> 
>>>> How does this vary across platforms? Is all of this being pushed down
>>>> to DT, because there is no coordination of this at the kernel ABI
>>>> level across platforms. In other words, why can't heap 0 be hardcoded
>>>> as system heap in the driver. It seems to me any 1 of these 3
>>>> properties could be used to derive the other 2.
>>> 
>>> The heap-id<->heap-type mapping isn't necessarily 1:1. As Laura
>>> indicated elsewhere on this thread, a given heap might need to be
>>> contiguous on one platform but not on another. In that case you just
>>> swap out the heap-type here and there's no need for userspace to change.
>>> 
>>> The heap-name, OTOH, could be derived from the heap-id, which is what we
>>> hackishly do here [1] and here[2].
>> 
>> By the way, since we agreed that heap id and heap type mappings
>> are not 1:1 - we have a problem with the current API.
>> 
>> In userspace we currently have this:
>> 
>> int ion_alloc(int fd, size_t len, size_t align, unsigned int heap_mask,
>> unsigned int flags, ion_user_handle_t *handle);
>> 
>> We do not specify here what TYPE of heap we want the allocation to come
>> from.
>> This may lead to very unpleasant stuff when porting from one platfrom to
>> another.

Okay, I may be totally missing some point here then.

> What "unpleasant stuff" are you referring to, exactly? 

It's not really clear for me how (and at where - kernel or userspace) 
we should properly sort out cases when the next device the pipeline 
introduces some constraints on the buffer it can use. 

For instance: camera can save data into a non-contiguous buffer, but the 
image processing hardware (that may or may not be involved) expects the 
buffer to be contiguous.

> Abstracting the
> heap type away from userspace has actually made our lives easier since
> userspace doesn't need to know anything about the properties of the
> underlying platform. It just asks for a buffer from the "camera" heap,
> for example. On some platforms that's contiguous, on others it's not.
> 
> -Mitch
> 
> --
> Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project

Regards, 
Andrew