From: Arnd Bergmann <arnd@arndb.de>
To: Grant Likely <grant.likely@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org,
Santosh Shilimkar <santosh.shilimkar@ti.com>,
linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
Grygorii Strashko <grygorii.strashko@ti.com>,
Russell King <linux@arm.linux.org.uk>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Linus Walleij <linus.walleij@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Olof Johansson <olof@lixom.net>
Subject: Re: [PATCH v3 4/7] of: configure the platform device dma parameters
Date: Tue, 27 May 2014 15:30:33 +0200 [thread overview]
Message-ID: <5840140.8yGnd4Ycx3@wuerfel> (raw)
In-Reply-To: <20140527125655.63A46C40FCB@trevor.secretlab.ca>
On Tuesday 27 May 2014 13:56:55 Grant Likely wrote:
> On Fri, 02 May 2014 11:58:30 +0200, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Thursday 01 May 2014 14:12:10 Grant Likely wrote:
> > > > > I've got two concerns here. of_dma_get_range() retrieves only the first
> > > > > tuple from the dma-ranges property, but it is perfectly valid for
> > > > > dma-ranges to contain multiple tuples. How should we handle it if a
> > > > > device has multiple ranges it can DMA from?
> > > > >
> > > >
> > > > We've not found any cases in current Linux where more than one dma-ranges
> > > > would be used. Moreover, The MM (definitely for ARM) isn't supported such
> > > > cases at all (if i understand everything right).
> > > > - there are only one arm_dma_pfn_limit
> > > > - there is only one MM zone is used for ARM
> > > > - some arches like x86,mips can support 2 zones (per arch - not per device or bus)
> > > > DMA & DMA32, but they configured once and forever per arch.
> > >
> > > Okay. If anyone ever does implement multiple ranges then this code will
> > > need to be revisited.
> >
> > I wonder if it's needed for platforms implementing the standard "ARM memory map" [1].
> > The document only talks about addresses as seen from the CPU, and I can see
> > two logical interpretations how the RAM is supposed to be visible from a device:
> > either all RAM would be visible contiguously at DMA address zero, or everything
> > would be visible at the same physical address as the CPU sees it.
> >
> > If anyone picks the first interpretation, we will have to implement that
> > in Linux. We can of course hope that all hardware designs follow the second
> > interpretation, which would be more convenient for us here.
>
> Indeed. Hope though we might, I would not be surprised to see a platform
> that does the first. In that case we could probably handle it with a
> ranges property that is DMA-controller facing instead of device facing.
> That would be able to handle the translation between CPU addressing and
> DMA addressing.
>
> Come to think of it, doesn't PCI DMA have to deal with that situation if
> the PCI window is not 1:1 mapped into the CPU address space?
I think all PCI buses we support so far only need a single entry in the
dma-ranges property.
Arnd
next prev parent reply other threads:[~2014-05-27 13:30 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-24 15:30 [PATCH v3 0/7] of: setup dma parameters using dma-ranges and dma-coherent Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 1/7] device: introduce per device dma_pfn_offset Santosh Shilimkar
2014-05-02 1:01 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 2/7] of: introduce of_dma_get_range() helper Santosh Shilimkar
2014-05-02 1:06 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 3/7] of: introduce of_dma_is_coherent() helper Santosh Shilimkar
2014-05-02 0:56 ` Rob Herring
2014-05-05 21:45 ` Santosh Shilimkar
2014-05-05 22:06 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 4/7] of: configure the platform device dma parameters Santosh Shilimkar
2014-04-29 14:41 ` Grant Likely
2014-04-30 14:19 ` Santosh Shilimkar
2014-05-01 13:12 ` Grant Likely
2014-05-01 13:16 ` Santosh Shilimkar
2014-05-02 9:58 ` Arnd Bergmann
2014-05-02 13:13 ` Santosh Shilimkar
2014-05-02 15:13 ` Arnd Bergmann
2014-05-27 12:56 ` Grant Likely
2014-05-27 13:30 ` Arnd Bergmann [this message]
2014-05-28 8:23 ` Linus Walleij
2014-05-28 13:29 ` Arnd Bergmann
2014-05-28 13:32 ` Linus Walleij
2014-05-28 14:04 ` Santosh Shilimkar
2014-05-29 14:01 ` Linus Walleij
2014-05-29 14:08 ` Santosh Shilimkar
2014-05-29 19:24 ` Arnd Bergmann
2014-05-29 20:04 ` Santosh Shilimkar
2014-05-02 0:49 ` Rob Herring
2014-05-05 21:47 ` Santosh Shilimkar
2014-05-05 22:08 ` Rob Herring
2014-05-06 9:40 ` Arnd Bergmann
2014-05-06 20:44 ` Santosh Shilimkar
2014-05-07 13:24 ` Santosh Shilimkar
2014-05-02 16:54 ` Bjorn Helgaas
2014-05-02 18:59 ` Arnd Bergmann
2014-05-05 20:45 ` Bjorn Helgaas
2014-05-05 20:55 ` Arnd Bergmann
2014-05-05 22:28 ` Bjorn Helgaas
2014-05-06 3:44 ` Benjamin Herrenschmidt
2014-05-06 9:54 ` Arnd Bergmann
2014-05-06 13:32 ` Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 5/7] ARM: dma: Use dma_pfn_offset for dma address translation Santosh Shilimkar
2014-05-02 14:32 ` Rob Herring
2014-05-02 14:58 ` Russell King - ARM Linux
2014-05-02 15:05 ` Santosh Shilimkar
2014-05-05 19:50 ` Russell King - ARM Linux
2014-05-05 21:43 ` Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 6/7] ARM: dma: implement set_arch_dma_coherent_ops() Santosh Shilimkar
2014-05-02 0:58 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 7/7] ARM: dma: use phys_addr_t in __dma_page_[cpu_to_dev/dev_to_cpu] Santosh Shilimkar
2014-04-24 15:45 ` Will Deacon
2014-05-01 13:19 ` [PATCH v3 0/7] of: setup dma parameters using dma-ranges and dma-coherent Santosh Shilimkar
2014-05-01 13:25 ` Russell King - ARM Linux
2014-05-01 14:06 ` Santosh Shilimkar
2014-05-02 14:41 ` Rob Herring
2014-05-02 16:41 ` Santosh Shilimkar
2014-05-14 10:12 ` Grant Likely
2014-06-02 6:37 ` Shawn Guo
2014-06-02 13:24 ` Santosh Shilimkar
2014-06-02 15:06 ` Arnd Bergmann
2014-06-02 15:54 ` Santosh Shilimkar
2014-06-02 19:00 ` Arnd Bergmann
2014-06-02 19:08 ` Santosh Shilimkar
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