From: Christoph Hellwig <hch@lst.de>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: iommu@lists.linux-foundation.org,
Robin Murphy <robin.murphy@arm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] dma-direct: document the zone selection logic
Date: Mon, 8 Oct 2018 09:03:27 +0200 [thread overview]
Message-ID: <20181008070327.GA3134@lst.de> (raw)
In-Reply-To: <20181001201016.32639-2-hch@lst.de>
Ben, does this resolve your issues with the confusing zone selection?
On Mon, Oct 01, 2018 at 01:10:16PM -0700, Christoph Hellwig wrote:
> What we are doing here isn't quite obvious, so add a comment explaining
> it.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> kernel/dma/direct.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index ba6f5956a291..14b966e2349a 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
> else
> *phys_mask = dma_to_phys(dev, dma_mask);
>
> - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
> + /*
> + * Optimistically try the zone that the physicall address mask falls
> + * into first. If that returns memory that isn't actually addressable
> + * we will fallback to the next lower zone and try again.
> + *
> + * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding
> + * zones.
> + */
> if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
> return GFP_DMA;
> if (*phys_mask <= DMA_BIT_MASK(32))
> --
> 2.19.0
>
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
---end quoted text---
next prev parent reply other threads:[~2018-10-08 7:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-01 20:10 document dma-direct zone selection Christoph Hellwig
2018-10-01 20:10 ` [PATCH] dma-direct: document the zone selection logic Christoph Hellwig
2018-10-01 20:22 ` Randy Dunlap
2018-10-08 7:03 ` Christoph Hellwig [this message]
2018-10-08 22:56 ` Benjamin Herrenschmidt
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=20181008070327.GA3134@lst.de \
--to=hch@lst.de \
--cc=benh@kernel.crashing.org \
--cc=iommu@lists.linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=robin.murphy@arm.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