linux-kernel - Re: Question about DMA

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Message-ID: <479D06E0.3090601@gmail.com>
Date:	Sun, 27 Jan 2008 23:34:08 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Francis Moreau <francis.moro@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Question about DMA

On 01/27/2008 09:51 PM, Francis Moreau wrote:
> Hello,
> 
> I have 2 questions regarding set_dma_addr(unsigned int channel,
> unsigned int addr) helper.
> 
> 1/  Why does the function take only one address ? I would expect it
> to take both a source and a destination address for the dma controller
> to transfer data.

since your device is responsible for sending data from/to local memory. ISA dma 
controller has only 2 registers -- 16-bit address to put incoming data to (get 
outcoming from) + 8-bit nonincrementing page and 16-bit counter.

> 2/ The type of address parameter is an unsigned int. Why isn't it a dma_addr_t
> type ?

since isa dma controller can address up to 2^24 (16-bit address + 8-bit page) 
bytes of memory, i.e. 16M.

Are you sure, you want use this API?

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