linux-kernel - Re: [PATCH 2.6.22.y] ieee1394: revert "sbp2: enforce 32bit DMA mapping"

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Message-id: <46B4B3DC.7020609@shaw.ca>
Date:	Sat, 04 Aug 2007 11:14:04 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	stable@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.22.y] ieee1394: revert "sbp2: enforce 32bit DMA mapping"

Stefan Richter wrote:
> Date: Wed, 1 Aug 2007 20:30:36 +0200 (CEST)
> From: Stefan Richter <stefanr@...6.in-berlin.de>
> Subject: ieee1394: revert "sbp2: enforce 32bit DMA mapping"
> 
> Revert commit 0555659d63c285ceb7ead3115532e1b71b0f27a7 from 2.6.22-rc1.
> The dma_set_mask call somehow failed on a PowerMac G5, PPC64:
> http://lkml.org/lkml/2007/8/1/344
> 
> Should there ever occur a DMA mapping beyond the physical DMA range, a
> proper SBP-2 firmware will report transport errors.  So let's leave it
> at that.

Isn't this a rather poor workaround? All this means is that if we fail 
to set a 32-bit DMA mask, we're likely to blow up at runtime instead of 
at initialization time, when we get a DMA mapping over 4GB.

If setting 32-bit DMA mask fails on ppc64, that sounds like a problem 
with the DMA implementation on that architecture. There are enough cards 
out there that only support 32-bit DMA that this really needs to work..

> 
> Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
> Tested-by: Olaf Hering <olh@...e.de>
> ---
> Same as commit a9c2f18800753c82c45fc13b27bdc148849bdbb2.
> 
>  drivers/ieee1394/sbp2.c |    5 -----
>  1 file changed, 5 deletions(-)
> 
> Index: linux-2.6.22/drivers/ieee1394/sbp2.c
> ===================================================================
> --- linux-2.6.22.orig/drivers/ieee1394/sbp2.c
> +++ linux-2.6.22/drivers/ieee1394/sbp2.c
> @@ -774,11 +774,6 @@ static struct sbp2_lu *sbp2_alloc_device
>  			SBP2_ERR("failed to register lower 4GB address range");
>  			goto failed_alloc;
>  		}
> -#else
> -		if (dma_set_mask(hi->host->device.parent, DMA_32BIT_MASK)) {
> -			SBP2_ERR("failed to set 4GB DMA mask");
> -			goto failed_alloc;
> -		}
>  #endif
>  	}
>  
> 

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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