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From: Catalin Marinas <catalin.marinas@arm.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, Will Deacon <Will.Deacon@arm.com>
Subject: Re: [PATCH v4 16/19] ARM: LPAE: Use generic dma_addr_t type definition
Date: Mon, 14 Feb 2011 13:01:30 +0000	[thread overview]
Message-ID: <1297688490.31111.38.camel@e102109-lin.cambridge.arm.com> (raw)
In-Reply-To: <20110212103413.GD15616@n2100.arm.linux.org.uk>

On Sat, 2011-02-12 at 10:34 +0000, Russell King - ARM Linux wrote:
> On Mon, Jan 24, 2011 at 05:55:58PM +0000, Catalin Marinas wrote:
> > From: Will Deacon <will.deacon@arm.com>
> >
> > This patch uses the types.h implementation in asm-generic to define the
> > dma_addr_t type as the same width as phys_addr_t.
> >
> > NOTE: this is a temporary patch until the corresponding patches unifying
> > the dma_addr_t and removing the dma64_addr_t are merged into mainline.
> 
> I'm not too sure about this patch.  All of the DMA devices we have only
> take 32-bit addresses for their DMA, so making dma_addr_t 64-bit seems
> wrong as we'll implicitly truncate these addresses.

If we don't enable LPAE, the dma_addr_t is 32-bit, so existing platforms
are not affected. With Cortex-A15, new platforms may have PCIe and be
able to access memory beyond 32-bit (if they don't support >32-bit DMA
at least for some critical devices, I'm not sure why they would use
A15).

For things like hard drives for example, it becomes problematic as pages
are allocated by the VFS layer from highmem and passed to the driver for
DMA. If we keep dma_addr_t to 32-bit you would need to use DMA bounce
even if the PCIe device supports >32-bit physical addresses.

> As ARM platforms don't (sanely) support DMA, I think dropping this patch
> for the time being would be a good idea, and stick with 32-bit dma_addr_t,
> especially as we need to first do a sweep for dma_addr_t usage in device
> driver structures (such as dma engine scatter lists.)  These really should
> use __le32/__be32/u32 depending on whether they're little endian, big
> endian or native endian.

Maybe we could make the dma_addr_t size configurable (and disabled by
default) since I expect there'll be platforms capable of >32-bit DMA.

-- 
Catalin



  reply	other threads:[~2011-02-14 13:01 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-24 17:55 [PATCH v4 00/19] ARM: Add support for the Large Physical Address Extensions Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 01/19] ARM: Make the argument to virt_to_phys() "const volatile" Catalin Marinas
2011-01-24 19:19   ` Stephen Boyd
2011-01-24 23:38     ` Russell King - ARM Linux
2011-01-25 10:00     ` Arnd Bergmann
2011-01-25 10:29       ` Russell King - ARM Linux
2011-01-25 14:14         ` Arnd Bergmann
2011-01-24 17:55 ` [PATCH v4 02/19] ARM: LPAE: Fix early_pte_alloc() assumption about the Linux PTE Catalin Marinas
2011-02-12  9:56   ` Russell King - ARM Linux
2011-01-24 17:55 ` [PATCH v4 03/19] ARM: LPAE: use long long format when printing physical addresses and ptes Catalin Marinas
2011-02-12  9:59   ` Russell King - ARM Linux
2011-01-24 17:55 ` [PATCH v4 04/19] ARM: LPAE: Use PMD_(SHIFT|SIZE|MASK) instead of PGDIR_* Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 05/19] ARM: LPAE: Factor out 2-level page table definitions into separate files Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 06/19] ARM: LPAE: Add (pte|pmd|pgd|pgprot)val_t type definitions as u32 Catalin Marinas
2011-02-03 17:13   ` Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 07/19] ARM: LPAE: Use a mask for physical addresses in page table entries Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 08/19] ARM: LPAE: Introduce the 3-level page table format definitions Catalin Marinas
2011-01-24 21:26   ` Nick Piggin
2011-01-24 21:42     ` Russell King - ARM Linux
2011-01-25 10:04       ` Catalin Marinas
2011-03-21 12:36       ` Catalin Marinas
2011-03-21 12:56         ` Russell King - ARM Linux
2011-03-21 13:19           ` Catalin Marinas
2011-02-03 17:11   ` Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 09/19] ARM: LPAE: Page table maintenance for the 3-level format Catalin Marinas
2011-02-03 17:09   ` Catalin Marinas
2011-02-03 17:56   ` Russell King - ARM Linux
2011-02-03 22:00     ` Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 10/19] ARM: LPAE: MMU setup for the 3-level page table format Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 11/19] ARM: LPAE: Add fault handling support Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 12/19] ARM: LPAE: Add context switching support Catalin Marinas
2011-02-12 10:44   ` Russell King - ARM Linux
2011-02-14 13:24     ` Catalin Marinas
2011-02-19 18:30       ` Russell King - ARM Linux
2011-02-19 23:16         ` Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 13/19] ARM: LPAE: Add identity mapping support for the 3-level page table format Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 14/19] ARM: LPAE: Add SMP " Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 15/19] ARM: LPAE: use phys_addr_t instead of unsigned long for physical addresses Catalin Marinas
2011-02-12 10:28   ` Russell King - ARM Linux
2011-02-15 11:52     ` Will Deacon
2011-02-15 12:35       ` Russell King - ARM Linux
2011-02-15 12:39         ` Catalin Marinas
2011-02-15 13:37           ` Will Deacon
2011-02-15 14:23             ` Russell King - ARM Linux
2011-02-15 15:26               ` Will Deacon
2011-02-15 15:48                 ` Russell King - ARM Linux
2011-02-19 18:26   ` Russell King - ARM Linux
2011-02-21 14:36     ` Will Deacon
2011-02-21 14:58       ` Russell King - ARM Linux
2011-02-21 15:01         ` Will Deacon
2011-01-24 17:55 ` [PATCH v4 16/19] ARM: LPAE: Use generic dma_addr_t type definition Catalin Marinas
2011-02-12 10:34   ` Russell King - ARM Linux
2011-02-14 13:01     ` Catalin Marinas [this message]
2011-02-15 14:27       ` Russell King - ARM Linux
2011-02-15 15:24         ` Catalin Marinas
2011-01-24 17:55 ` [PATCH v4 17/19] ARM: LPAE: mark memory banks with start > ULONG_MAX as highmem Catalin Marinas
2011-02-12 10:36   ` Russell King - ARM Linux
2011-01-24 17:56 ` [PATCH v4 18/19] ARM: LPAE: add support for ATAG_MEM64 Catalin Marinas
2011-01-24 17:56 ` [PATCH v4 19/19] ARM: LPAE: Add the Kconfig entries Catalin Marinas

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