From: Christoph Hellwig <hch@lst.de>
To: Ruizhe Zhou <zhouruizhe@resnics.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Jonathan Corbet <corbet@lwn.net>, Christoph Hellwig <hch@lst.de>,
Frank Li <Frank.li@oss.nxp.com>,
Shuah Khan <skhan@linuxfoundation.org>,
Randy Dunlap <rdunlap@infradead.org>,
linux-doc@vger.kernel.org, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] docs: dma-api: require checking DMA mask setup errors
Date: Mon, 7 Sep 2026 07:47:33 +0200 [thread overview]
Message-ID: <20260907054733.GA31481@lst.de> (raw)
In-Reply-To: <20260907054400.1088151-1-zhouruizhe@resnics.com>
On Mon, Sep 07, 2026 at 01:44:00PM +0800, Ruizhe Zhou wrote:
> The DMA HOWTO says dma_set_mask_and_coherent() cannot fail for
> DMA_BIT_MASK(64), and more generally for masks wider than 32 bits. It
> consequently recommends calls to discard the check for return value.
>
> The generic direct-DMA path does accept every mask of at least 32 bits,
> but that is not an API-wide success guarantee. Backend callbacks can
> reject wider masks: ibmebus_dma_supported() and
> xen_grant_dma_supported() accept only DMA_BIT_MASK(64), so a 40-bit mask
> fails.
Please fix them as they break the very sensible API guarantees
instead of officially sanctioning this behavior.
>
> Even DMA_BIT_MASK(64) can fail when DMA setup is unavailable or
> inconsistent. For example, dma_dummy_supported() rejects every mask.
So? Did you actually try to understand this code or is this just dumb
agent work?
next prev parent reply other threads:[~2026-09-07 5:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-07 5:44 Ruizhe Zhou
2026-09-07 5:47 ` Christoph Hellwig [this message]
2026-09-07 7:34 ` Ruizhe Zhou
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260907054733.GA31481@lst.de \
--to=hch@lst.de \
--cc=Frank.li@oss.nxp.com \
--cc=corbet@lwn.net \
--cc=iommu@lists.linux.dev \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=m.szyprowski@samsung.com \
--cc=rdunlap@infradead.org \
--cc=robin.murphy@arm.com \
--cc=skhan@linuxfoundation.org \
--cc=zhouruizhe@resnics.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®