From: Christoph Hellwig <hch@lst.de>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Bjorn Helgaas <bhelgaas@google.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Hanjun Guo <guohanjun@huawei.com>,
Sudeep Holla <sudeep.holla@arm.com>, Jens Axboe <axboe@kernel.dk>,
Joerg Roedel <joro@8bytes.org>, Rob Herring <robh+dt@kernel.org>,
Frank Rowand <frowand.list@gmail.com>,
Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
phil@raspberrypi.org, Ralf Baechle <ralf@linux-mips.org>,
Paul Burton <paulburton@kernel.org>,
James Hogan <jhogan@kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Len Brown <lenb@kernel.org>,
linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-pci@vger.kernel.org,
linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-ide@vger.kernel.org, iommu@lists.linux-foundation.org,
devicetree@vger.kernel.org
Subject: Re: [PATCH] dma-mapping: treat dev->bus_dma_mask as a DMA limit
Date: Thu, 14 Nov 2019 08:34:59 +0100 [thread overview]
Message-ID: <20191114073459.GB26546@lst.de> (raw)
In-Reply-To: <20191113161340.27228-1-nsaenzjulienne@suse.de>
On Wed, Nov 13, 2019 at 05:13:39PM +0100, Nicolas Saenz Julienne wrote:
> Using a mask to represent bus DMA constraints has a set of limitations.
> The biggest one being it can only hold a power of two (minus one). The
> DMA mapping code is already aware of this and treats dev->bus_dma_mask
> as a limit. This quirk is already used by some architectures although
> still rare.
>
> With the introduction of the Raspberry Pi 4 we've found a new contender
> for the use of bus DMA limits, as its PCIe bus can only address the
> lower 3GB of memory (of a total of 4GB). This is impossible to represent
> with a mask. To make things worse the device-tree code rounds non power
> of two bus DMA limits to the next power of two, which is unacceptable in
> this case.
>
> In the light of this, rename dev->bus_dma_mask to dev->bus_dma_limit all
> over the tree and treat it as such. Note that dev->bus_dma_limit is
> meant to contain the higher accesible DMA address.
This looks sensible modulo the minor comments in this thread.
>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
>
> ---
>
> Note this is rebased on top of Christoph's latest DMA series:
> https://www.spinics.net/lists/arm-kernel/msg768600.html
FYI, I'll plan to merge those tonight unless anyone screams.
next prev parent reply other threads:[~2019-11-14 7:35 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-13 16:13 [PATCH] dma-mapping: treat dev->bus_dma_mask as a DMA limit Nicolas Saenz Julienne
2019-11-13 20:34 ` Robin Murphy
2019-11-13 20:41 ` Florian Fainelli
2019-11-13 21:24 ` Robin Murphy
2019-11-14 9:47 ` Nicolas Saenz Julienne
2019-11-14 7:34 ` Christoph Hellwig [this message]
2019-11-19 12:57 ` Nicolas Saenz Julienne
2019-11-19 17:00 ` Christoph Hellwig
2019-11-19 17:17 ` Robin Murphy
2019-11-21 7:31 ` Christoph Hellwig
2019-11-21 9:18 ` Nicolas Saenz Julienne
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=20191114073459.GB26546@lst.de \
--to=hch@lst.de \
--cc=axboe@kernel.dk \
--cc=benh@kernel.crashing.org \
--cc=bhelgaas@google.com \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=devicetree@vger.kernel.org \
--cc=frowand.list@gmail.com \
--cc=guohanjun@huawei.com \
--cc=hpa@zytor.com \
--cc=iommu@lists.linux-foundation.org \
--cc=jhogan@kernel.org \
--cc=joro@8bytes.org \
--cc=lenb@kernel.org \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-ide@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=lorenzo.pieralisi@arm.com \
--cc=luto@kernel.org \
--cc=m.szyprowski@samsung.com \
--cc=mingo@redhat.com \
--cc=mpe@ellerman.id.au \
--cc=nsaenzjulienne@suse.de \
--cc=paulburton@kernel.org \
--cc=paulus@samba.org \
--cc=peterz@infradead.org \
--cc=phil@raspberrypi.org \
--cc=ralf@linux-mips.org \
--cc=rjw@rjwysocki.net \
--cc=robh+dt@kernel.org \
--cc=robin.murphy@arm.com \
--cc=sudeep.holla@arm.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/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;
as well as URLs for NNTP newsgroup(s).