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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.

  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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