linux-kernel - Re: [PATCH v2 7/8] docs: dma-api: update streaming DMA physical address constraints

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Message-ID: <337ea10d-d6b6-496e-b1e3-4ee912067e8e@infradead.org>
Date: Sat, 28 Jun 2025 11:59:31 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Petr Tesarik <ptesarik@...e.com>, Jonathan Corbet <corbet@....net>,
 Robin Murphy <robin.murphy@....com>,
 Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Keith Busch
 <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
 Bagas Sanjaya <bagasdotme@...il.com>,
 "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>, iommu@...ts.linux.dev
Subject: Re: [PATCH v2 7/8] docs: dma-api: update streaming DMA physical
 address constraints



On 6/27/25 3:10 AM, Petr Tesarik wrote:
> Add an introductory paragraph to Part Id - Streaming DMA mappings and move
> the explanation of address constraints there, because it applies to all map
> functions.
> 
> Clarify that streaming DMA can be used with memory which does not meet the
> addressing constraints of a device, but it may fail in that case.
> 
> Make a note about SWIOTLB and link to the detailed description of it.
> 
> Do not mention platform-dependent allocation flags. The note may mislead
> device driver authors into thinking that they should poke into and try to
> second-guess the DMA API implementation. They definitely shouldn't.
> 
> Remove the claim that platforms with an IOMMU may not require physically
> contiguous buffers. The current implementation explicitly rejects vmalloc
> addresses, regardless of IOMMU.
> 
> Signed-off-by: Petr Tesarik <ptesarik@...e.com>

Tested-by: Randy Dunlap <rdunlap@...radead.org>

Thanks.

> ---
>  Documentation/core-api/dma-api.rst | 36 +++++++++++++++++-------------
>  1 file changed, 21 insertions(+), 15 deletions(-)

-- 
~Randy