linux-kernel - Re: [RFC/RFT PATCH 3/5] scsi: Use dma_max_pfn(dev) helper for bounce

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Message-ID: <51E07B6E.5090900@cogentembedded.com>
Date:	Sat, 13 Jul 2013 01:55:58 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>,
	linux-scsi@...r.kernel.org
Subject: Re: [RFC/RFT PATCH 3/5] scsi: Use dma_max_pfn(dev) helper for bounce_limit
 calculations

Hello.

On 07/13/2013 01:48 AM, Santosh Shilimkar wrote:

> DMA bounce limit is the maximum direct DMA'able memory beyond which
> bounce buffers has to be used to perform dma operations. SCSI driver
> relies on dma_mask but its calculation is based on max_*pfn which
> don't have uniform meaning across architectures. So make use of
> dma_max_pfn() which is expected to return the DMAable maximum pfn
> value across architectures.

> Cc: Russell King <linux@....linux.org.uk>
> Cc: linux-scsi@...r.kernel.org

> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@...com>
> ---
>   drivers/scsi/scsi_lib.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 86d5220..e8275fa 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1668,7 +1668,7 @@ u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
>
>   	host_dev = scsi_get_device(shost);
>   	if (host_dev && host_dev->dma_mask)
> -		bounce_limit = *host_dev->dma_mask;
> +		bounce_limit = dma_max_pfn(host_dev) << PAGE_SHIFT;

    You definitely forgot -1 here.

WBR, Sergei

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