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

[Mitchel Humpherys]

On Tue, Oct 06 2015 at 05:35:41 PM, Rob Herring <robherring2@xxxxxxxxx> wrote:
> On Tue, Oct 6, 2015 at 3:47 PM, Laura Abbott <labbott@xxxxxxxxxxxxxxxxx> 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].

[1] https://www.codeaurora.org/cgit/quic/la/kernel/msm-3.14/tree/drivers/staging/android/ion/msm/msm_ion.c?h=msm-3.14#n53
[2] https://www.codeaurora.org/cgit/quic/la/kernel/msm-3.14/tree/drivers/staging/android/ion/msm/msm_ion.c?h=msm-3.14#n398


-Mitch

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