From: Wolfram Sang <wsa+renesas@sang-engineering.com>
To: iommu@lists.linux-foundation.org, Robin Murphy <robin.murphy@arm.com>
Cc: linux-renesas-soc@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
linux-kernel@vger.kernel.org,
Wolfram Sang <wsa+renesas@sang-engineering.com>
Subject: [RFC PATCH 0/2] dma-mapping: introduce helper for setting dma_parms
Date: Tue, 11 Sep 2018 18:30:48 +0200 [thread overview]
Message-ID: <20180911163050.28072-1-wsa+renesas@sang-engineering.com> (raw)
Hi all,
commit 78c47830a5cb ("dma-debug: check scatterlist segments") triggers
for Renesas hardware I look after, so thanks for pointing out we should
have proper dma_parms for our DMA providers.
When trying to fix it, I became a bit puzzled about the life cycle of
the pointer to dma_parms. AFAIU most drivers leave the pointer dangling
on driver unbind. Check drivers/dma/bcm2835-dma.c, for example:
od = devm_kzalloc(&pdev->dev, sizeof(*od), GFP_KERNEL);
if (!od)
return -ENOMEM;
pdev->dev.dma_parms = &od->dma_parms;
dma_set_max_seg_size(&pdev->dev, 0x3FFFFFFF);
And that's all about handling dma_parms. So, on unbind, the memory for
'od' gets freed and dma_params is a dangling pointer.
drivers/gpu/drm/exynos/exynos_drm_iommu.c seems to do it correctly:
static inline int configure_dma_max_seg_size(struct device *dev)
{
if (!dev->dma_parms)
dev->dma_parms = kzalloc(sizeof(*dev->dma_parms), GFP_KERNEL);
if (!dev->dma_parms)
return -ENOMEM;
dma_set_max_seg_size(dev, DMA_BIT_MASK(32));
return 0;
}
static inline void clear_dma_max_seg_size(struct device *dev)
{
kfree(dev->dma_parms);
dev->dma_parms = NULL;
}
But this seems error prone and quite some code to add for every DMA
provider. So, I wondered if we couldn't have a helper for that. After
some brainstorming, I favour a dmam_-type of function. It will ensure
the memory gets freed and the pointer cleared on unbind. And it should
be easy to use.
I attached an RFC which I tested on a Renesas R-Car H3 SoC with the internal
DMAC of the SD controller. A branch can be found here (still waiting for
buildbot results):
git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/sdhi/set_max_seg
I added the companion function dmam_free_dma_parms() for completeness
although there is no user yet. I'd be totally open to drop it until
someone needs it.
Please let me know what you think. If this is the right track, I'll be
willing to fix the dangling pointers with it, too.
Thanks and happy hacking,
Wolfram
Wolfram Sang (2):
dma-mapping: introduce helper for setting dma_parms
mmc: sdhi: internal_dmac: set dma_parms
drivers/mmc/host/renesas_sdhi_internal_dmac.c | 2 +
include/linux/dma-mapping.h | 5 ++
kernel/dma/mapping.c | 50 +++++++++++++++++++
3 files changed, 57 insertions(+)
--
2.18.0
next reply other threads:[~2018-09-11 16:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-11 16:30 Wolfram Sang [this message]
2018-09-11 16:30 ` [RFC PATCH 1/2] dma-mapping: introduce helper for setting dma_parms Wolfram Sang
2018-09-11 16:30 ` [RFC PATCH 2/2] mmc: sdhi: internal_dmac: set dma_parms Wolfram Sang
2018-09-11 17:24 ` [RFC PATCH 0/2] dma-mapping: introduce helper for setting dma_parms Robin Murphy
2018-09-11 23:39 ` Wolfram Sang
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=20180911163050.28072-1-wsa+renesas@sang-engineering.com \
--to=wsa+renesas@sang-engineering.com \
--cc=hch@lst.de \
--cc=iommu@lists.linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-renesas-soc@vger.kernel.org \
--cc=m.szyprowski@samsung.com \
--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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.