From: Christoph Hellwig <hch@lst•de>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse•de>
Cc: Peter Zijlstra <peterz@infradead•org>,
Benjamin Herrenschmidt <benh@kernel•crashing.org>,
Dave Hansen <dave.hansen@linux•intel.com>,
linux-pci@vger•kernel.org, linux-kernel@vger•kernel.org,
linux-ide@vger•kernel.org, Paul Mackerras <paulus@samba•org>,
Hanjun Guo <guohanjun@huawei•com>,
Frank Rowand <frowand.list@gmail•com>,
Christoph Hellwig <hch@lst•de>,
Marek Szyprowski <m.szyprowski@samsung•com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm•com>,
"H. Peter Anvin" <hpa@zytor•com>,
Paul Burton <paulburton@kernel•org>,
Michael Ellerman <mpe@ellerman•id.au>,
Joerg Roedel <joro@8bytes•org>,
x86@kernel•org, phil@raspberrypi•org, linux-acpi@vger•kernel.org,
Ingo Molnar <mingo@redhat•com>, James Hogan <jhogan@kernel•org>,
Len Brown <lenb@kernel•org>,
devicetree@vger•kernel.org, Rob Herring <robh+dt@kernel•org>,
Borislav Petkov <bp@alien8•de>, Andy Lutomirski <luto@kernel•org>,
Bjorn Helgaas <bhelgaas@google•com>,
Thomas Gleixner <tglx@linutronix•de>,
linux-arm-kernel@lists•infradead.org,
Jens Axboe <axboe@kernel•dk>,
linuxppc-dev@lists•ozlabs.org,
"Rafael J. Wysocki" <rjw@rjwysocki•net>,
linux-mips@vger•kernel.org, Ralf Baechle <ralf@linux-mips•org>,
iommu@lists•linux-foundation.org,
Sudeep Holla <sudeep.holla@arm•com>,
Robin Murphy <robin.murphy@arm•com>
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.
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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
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