linux-kernel - Re: [PATCH v2] PL330: Add PL330 DMA controller driver

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Date:	Thu, 25 Mar 2010 18:01:00 +0900
From:	Joonyoung Shim <jy0922.shim@...sung.com>
To:	Marc Zyngier <maz@...terjones.org>
Cc:	dan.j.williams@...el.com, linus.ml.walleij@...il.com,
	kyungmin.park@...sung.com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] PL330: Add PL330 DMA controller driver

On 3/25/2010 2:44 PM, Marc Zyngier wrote:
> On Thu, 25 Mar 2010 12:17:15 +0900
> Joonyoung Shim <jy0922.shim@...sung.com> wrote:
> 
>> +/* instruction set functions */
>> +static inline int pl330_dmaaddh(u8 *desc_pool_virt, u16 imm, bool ra)
>> +{
>> +	u8 opcode = DMAADDH | (ra << 1);
>> +
>> +	writeb(opcode, desc_pool_virt++);
> 
> desc_pool_virt is a virtual address (from dma_alloc_coherent). In such
> case, write[bwl] seems to be the wrong interface. I suggest the
> following code:
> 
> 	*desc_pool_virt++ = opcode;
> 
>> +	writew(imm, desc_pool_virt);
> 

Right. The write[bwl] is api for address ioremapped of io device. I will
change these.

> Does anything ensure that this won't generate an unaligned access?
> 

PL330 DMA controller fetches variable length instructions that consist of
one to six bytes, so i think unaligned access is no problem.

>> +	return 3;
>> +}
> 
> 	M.

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