linux-kernel - Re: [PATCH] mm: export cma alloc and release

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Date:   Mon, 7 Oct 2019 10:06:40 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yue Hu <huyue2@...ong.com>, Mike Rapoport <rppt@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ryohei Suzuki <ryh.szk.cmnty@...il.com>,
        Doug Berger <opendmb@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Peng Fan <peng.fan@....com>, linux-mm@...ck.org,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH] mm: export cma alloc and release

On 10/7/19 9:53 AM, Christoph Hellwig wrote:
> On Mon, Oct 07, 2019 at 09:50:31AM -0700, Mark Salyzyn wrote:
>> On 10/5/19 1:37 AM, Christoph Hellwig wrote:
>>> On Thu, Oct 03, 2019 at 09:55:28AM +0100, Catalin Marinas wrote:
>>>> Aren't drivers supposed to use the DMA API for such allocations rather
>>>> than invoking cma_*() directly?
>>> Yes, they are.
>> We have an engineer assigned to rewriting the ion memory driver to use
>> dma_buf interfaces. Hopefully that effort will solve the problem of
>> requiring these interfaces to be exported so that that driver (and others)
>> can be modularized.
>>
>> Thanks for the reviews, drop this patch from the list and we will regroup,
>> and accept that standing code in the kernel can not be modularized for the
>> moment.
> How is that different from the "DMA-BUF Heaps (destaging ION)" series
> floating around?

IDK, I am asking around because I am only superficially aware of that 
effort. Please view this as the left hand does not know what the right 
hand is doing. My issue was with a series of out-of-tree drivers that 
use the calls, and noted that currently the ion driver is using them as 
well, as rationalization for a 'user' for the export. I am pushing back 
on those out-of-tree drivers to switch their CMA interfaces to a modern 
approach as a result of these reviews; the result of this review had a 
positive effect because I was considering exporting them in the Android 
distro as a minimum, and now I am soundly rejecting that approach.

Sincerely -- Mark Salyzyn