linux-kernel - Re: [RFC v1 3/4] swiotlb: Allow dynamic allocation of bounce buffers

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Message-ID: <f9aec7fa-4b7a-65a3-c060-6c69298fc73b@huawei.com>
Date:   Thu, 13 Apr 2023 13:09:46 +0200
From:   Petr Tesarik <petr.tesarik.ext@...wei.com>
To:     Christoph Hellwig <hch@....de>
CC:     Jonathan Corbet <corbet@....net>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Borislav Petkov <bp@...e.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Kim Phillips <kim.phillips@....com>,
        "Steven Rostedt (Google)" <rostedt@...dmis.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Alexander Graf <graf@...zon.com>
Subject: Re: [RFC v1 3/4] swiotlb: Allow dynamic allocation of bounce buffers

On 4/7/2023 12:15 PM, Petr Tesařík wrote:
> On Fri, 7 Apr 2023 07:57:04 +0200
> Christoph Hellwig <hch@....de> wrote:
>[...]>> (Btw, in case anyone is interested, we really need to get started
>> on moving the dma fields out of struct device into a sub-struct
>> only allocated for DMA capable busses)
> 
> I like this idea. In fact, my WIP topic branch now moves the swiotlb
> fields into a separate struct, but I can surely go further and move all
> DMA-related fields.

I have looked into this now, and it looks like a nice cleanup. The
challenge is to get these patches reviewed by all affected maintainers,
and it would be blocking my work on dynamically allocated bounce buffers.

How about moving only some fields initially (coherent override, cma and
swiotlb)? These few are not used outside kernel/dma, but at least the
swiotlb part makes my patches easier to follow. I can move the rest as
soon as the dynamic patch series is merged.

Petr Tesarik