From: Santosh Shilimkar <santosh.shilimkar@ti.com>
To: Arnd Bergmann <arnd@arndb.de>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Cc: Grant Likely <grant.likely@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"Strashko, Grygorii" <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: Fri, 2 May 2014 09:13:48 -0400 [thread overview]
Message-ID: <53639A0C.8070306@ti.com> (raw)
In-Reply-To: <5279118.J5305KQNjB@wuerfel>
On Friday 02 May 2014 05:58 AM, Arnd Bergmann 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.
>
not sure if I got your point correctly but DMA address 0 isn't used as DRAM start in
any of the ARM SOC today, mainly because of the boot architecture where address 0 is
typically used by ROM code. RAM start will be at some offset always and hence I
believe ARM SOCs will follow second interpretation. This was one of the main reason
we ended up fixing the max*pfn stuff.
26ba47b {ARM: 7805/1: mm: change max*pfn to include the physical offset of memory}
>
> [1] http://infocenter.arm.com/help/topic/com.arm.doc.den0001c/DEN0001C_principles_of_arm_memory_maps.pdf
>
Regards,
Santosh
next prev parent reply other threads:[~2014-05-02 13:14 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 [this message]
2014-05-02 15:13 ` Arnd Bergmann
2014-05-27 12:56 ` Grant Likely
2014-05-27 13:30 ` Arnd Bergmann
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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