linux-kernel - RE: [PATCH v2] fsldma: add support to 36-bit physical address

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Date:	Fri, 12 Nov 2010 11:16:46 +0800
From:	Li Yang-R58472 <r58472@...escale.com>
To:	Kumar Gala <galak@...nel.crashing.org>
CC:	<dan.j.williams@...el.com>, <linuxppc-dev@...ts.ozlabs.org>,
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] fsldma: add support to 36-bit physical address

>Subject: Re: [PATCH v2] fsldma: add support to 36-bit physical address
>
>
>On Nov 11, 2010, at 6:16 AM, Li Yang wrote:
>
>> Expand the dma_mask of fsldma device to 36-bit, indicating that the
>> DMA engine can deal with 36-bit physical address and does not need the
>> SWIOTLB to create bounce buffer for it when doing dma_map_*().
>>
>> Signed-off-by: Li Yang <leoli@...escale.com>
>> ---
>> Add more detailed commit message
>>
>> drivers/dma/fsldma.c |    4 +++-
>> 1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c index
>> cea08be..8c79b37 100644
>> --- a/drivers/dma/fsldma.c
>> +++ b/drivers/dma/fsldma.c
>> @@ -1,7 +1,7 @@
>> /*
>>  * Freescale MPC85xx, MPC83xx DMA Engine support
>>  *
>> - * Copyright (C) 2007 Freescale Semiconductor, Inc. All rights reserved.
>> + * Copyright (C) 2007-2010 Freescale Semiconductor, Inc. All rights
>reserved.
>>  *
>>  * Author:
>>  *   Zhang Wei <wei.zhang@...escale.com>, Jul 2007
>> @@ -1338,6 +1338,8 @@ static int __devinit fsldma_of_probe(struct
>platform_device *op,
>> 	fdev->common.device_control = fsl_dma_device_control;
>> 	fdev->common.dev = &op->dev;
>>
>> +	dma_set_mask(&(op->dev), DMA_BIT_MASK(36));
>> +
>
>Is there any reason we shouldn't set DMA_BIT_MASK(64) since the DMA block
>programming model allows the address to be 64-bits?

The current code is only verified on chips with 36-bit physical address.  I'm not sure if the driver can work without any change on the 64-bit chip, although the register model suggests it can work well with 64-bit.  If you can confirm that it's compatible with the block on 64-bit chip, then we can change it to 64 bit dma mask.

- Leo

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