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 16:24:57 +0100 [thread overview]
Message-ID: <20191121152457.GA525@lst.de> (raw)
In-Reply-To: <20191121092646.8449-1-nsaenzjulienne@suse.de>
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.
next prev parent reply other threads:[~2019-11-21 15:25 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 [this message]
2019-11-21 15:26 ` Nicolas Saenz Julienne
2019-11-21 15:26 ` Christoph Hellwig
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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