linux-kernel - Re: [PATCH] dma-buf: heaps: Introduce dma_heap_add

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Message-ID: <eacfc713-e98a-78fa-b316-3943600813d0@socionext.com>
Date:   Fri, 31 Jul 2020 18:32:41 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        "Andrew F . Davis" <afd@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <Brian.Starkey@....com>,
        Christian Koenig <christian.koenig@....com>,
        linux-media@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dma-buf: heaps: Introduce dma_heap_add_cma() for
 non-default CMA heap

Hi John,
Thank you for your comment.

On 2020/07/29 4:17, John Stultz wrote:
> On Thu, Jul 16, 2020 at 6:10 PM Kunihiko Hayashi
> <hayashi.kunihiko@...ionext.com> wrote:
>>
>> Current dma-buf heaps can handle only default CMA. This introduces
>> dma_heap_add_cma() function to attach CMA heaps that belongs to a device.
>>
>> At first, the driver calls of_reserved_mem_device_init() to set
>> memory-region property associated with reserved-memory defined as CMA
>> to the device. And when the driver calls this dma_heap_add_cma(),
>> the CMA will be added to dma-buf heaps.
>>
>> For example, prepare CMA node named "linux,cma@...00000" and
>> specify the node for memory-region property. After the above calls
>> in the driver, a device file "/dev/dma_heap/linux,cma@...00000"
>> associated with the CMA become available as dma-buf heaps.
>>
>> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
>> ---
>>   drivers/dma-buf/heaps/cma_heap.c | 12 ++++++++++++
>>   include/linux/dma-heap.h         |  9 +++++++++
>>   2 files changed, 21 insertions(+)
> 
> Hey! Sorry for the slow response on this! I just realized I never replied!

I waited but no problem.

> 
>> diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
>> index 626cf7f..5d2442e 100644
>> --- a/drivers/dma-buf/heaps/cma_heap.c
>> +++ b/drivers/dma-buf/heaps/cma_heap.c

[snip]

>> --
>> 2.7.4
> 
> Looks sane to me.  Being able to expose different multiple CMA heaps
> is needed, and I agree this way (as opposed to my earlier dts
> appraoch) is probably the best approach. The only bit I'm so-so on is
> adding the CMA heap specific call in the dma-heap.h, but at the same
> time I can't justify adding a whole new header for a single function.

I'm also a little worried about whether "CMA specific" call is in
the dma-heap.h, however I can't find another solution.

> Do you have a upstream driver that you plan to make use this new call?

Unfortunately I don't have an upstream driver using this call.

This call is called from dma-buf heaps "importer" or "customer",
and I only made an example (do nothing) importer driver
to test the call.

> We want to have in-tree users of code added.

I think this is a generic way to use non-default CMA heaps, however,
we need in-tree "importer" drivers to want to use non-default CMA heaps.
I don't find it from now.

> But if so, feel free to add my:
>    Acked-by: John Stultz <john.stultz@...aro.org>
> To this patch when you submit the driver changes.

Thank you,

---
Best Regards
Kunihiko Hayashi