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Subject: Does pci_map_single magicly work on > 32 bit address for 32bit
 capable device?
From: Maxim Levitsky <maximlevitsky@gmail.com>
To: linux-kernel <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Date: Fri, 11 Dec 2009 23:39:42 +0200
Message-ID: <1260567582.5983.23.camel@maxim-laptop>
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Hi,

I am writing a driver, and I am faced with following problem:

I receive a kernel pointer, and I want device to dma into that memory.
However, device is only capable of 32 bit dma.

I can create a 'consistent' mapping and use memcpy from/to it, but it
feels like waste of performance.


According to Documentation/DMA-mapping.txt, I can tell that hw supports
32 bit dma using pci_set_dma_mask, however, what will happen if I pass
arbitrary kernel address into pci_map_single.
What will happen if the address is above 32 bit?

I tried to follow source of pci_map_single, but it is quite strongly
buried.
Also note that I don't need any scatter gather lists, because buffer
will always be 512 bytes long.


Note that I don't write the block driver itself, but a small driver that
plugs into that driver.
I am writing a driver for mtd subsystem and more precisely a nand
driver.

Unfortunately mtd system can call the driver with arbitrary kernel
pointer, although I am sure its not vmalloc'ed.
Usually it passes the pointer that is received from block subsystem.


Thanks in advance,
Maxim Levitsky

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