linux-kernel - Re: [PATCH] dma-buf: add DMA_BUF_IOCTL_SYNC

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Message-ID: <9e6f1f52-db49-43bb-a0c2-b0ad12c28aa1@amd.com>
Date: Mon, 8 Apr 2024 09:58:34 +0200
From: Christian König <christian.koenig@....com>
To: Rong Qianfeng <rongqianfeng@...o.com>, Jianqun Xu
 <jay.xu@...k-chips.com>, sumit.semwal@...aro.org
Cc: pekka.paalanen@...labora.com, daniel.vetter@...ll.ch,
 jason@...kstrand.net, linux-media@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
 linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH] dma-buf: add DMA_BUF_IOCTL_SYNC_PARTIAL support

Am 07.04.24 um 09:50 schrieb Rong Qianfeng:
> [SNIP]
>> Am 13.11.21 um 07:22 schrieb Jianqun Xu:
>>> Add DMA_BUF_IOCTL_SYNC_PARTIAL support for user to sync dma-buf with
>>> offset and len.
>>
>> You have not given an use case for this so it is a bit hard to 
>> review. And from the existing use cases I don't see why this should 
>> be necessary.
>>
>> Even worse from the existing backend implementation I don't even see 
>> how drivers should be able to fulfill this semantics.
>>
>> Please explain further,
>> Christian.
> Here is a practical case:
> The user space can allocate a large chunk of dma-buf for 
> self-management, used as a shared memory pool.
> Small dma-buf can be allocated from this shared memory pool and 
> released back to it after use, thus improving the speed of dma-buf 
> allocation and release.
> Additionally, custom functionalities such as memory statistics and 
> boundary checking can be implemented in the user space.
> Of course, the above-mentioned functionalities require the 
> implementation of a partial cache sync interface.

Well that is obvious, but where is the code doing that?

You can't send out code without an actual user of it. That will 
obviously be rejected.

Regards,
Christian.

>
> Thanks
> Rong Qianfeng.