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>,
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 v2] dma-mapping: treat dev->bus_dma_mask as a DMA limit
Date: Thu, 21 Nov 2019 16:26:50 +0100 [thread overview]
Message-ID: <20191121152650.GA651@lst.de> (raw)
In-Reply-To: <20191121152457.GA525@lst.de>
On Thu, Nov 21, 2019 at 04:24:57PM +0100, Christoph Hellwig wrote:
> On Thu, Nov 21, 2019 at 10:26:44AM +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 should
> > contain the higher accesible DMA address.
> >
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
>
> I've tentatively added this patch to the dma-mapping tree based on
> Robins principal approval of the last version. That way tomorrows
> linux-next run should still pick it up.
Actually. This doesn't apply because the dma-mapping tree doesn't
have you zone_dma_bits change. I guess we'll need to wait for the
next merge window, or maybe post rc1 if this happens to fix the
powerpc problem that Christian reported.
next prev parent reply other threads:[~2019-11-21 15:26 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-21 9:26 [PATCH v2] dma-mapping: treat dev->bus_dma_mask as a DMA limit Nicolas Saenz Julienne
2019-11-21 15:24 ` Christoph Hellwig
2019-11-21 15:26 ` Nicolas Saenz Julienne
2019-11-21 15:26 ` Christoph Hellwig [this message]
2019-11-21 15:55 ` Robin Murphy
2019-11-21 16:02 ` Christoph Hellwig
2019-11-21 16:53 ` Will Deacon
2019-11-21 17:16 ` Christoph Hellwig
2019-11-21 17:07 ` Robin Murphy
2019-11-21 17:17 ` Christoph Hellwig
2019-11-23 16:51 ` Nathan Chancellor
2019-11-25 7:44 ` Christoph Hellwig
2019-11-25 16:33 ` Robin Murphy
2019-11-26 18:51 ` Nicolas Saenz Julienne
2019-11-26 21:45 ` Robin Murphy
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