Re: [PATCH v2] ufs: adjust queue settings to PRDT limitations

[Subhash Jadavani <subhashj@codeaurora.org>]

Looks good to me.

Reviewed-by: Subhash Jadavani <subhashj@codeaurora.org>

On 9/25/2013 7:17 PM, Akinobu Mita wrote:
> The data byte count field of PRDT indicates the length of data block
> which is a segment of data transfer for SCSI commands.  The value of
> this field shall have Dword granularity and the the maximum of length
> is 256KB.
>
> This adjusts dma pad mask and max segment size to the above-mentioned
> PRDT limitations.
>
> Signed-off-by: Akinobu Mita <mita@fixstars.com>
> Cc: Subhash Jadavani <subhashj@codeaurora.org>
> Cc: Vinayak Holikatti <vinholikatti@gmail.com>
> Cc: Santosh Y <santoshsy@gmail.com>
> Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
> Cc: linux-scsi@vger.kernel.org
> ---
> * Change from v1
> - Add comments for PRDT limitations as suggested by Subhash Jadavani
>
>   drivers/scsi/ufs/ufshcd.c | 15 +++++++++++++++
>   drivers/scsi/ufs/ufshci.h |  5 +++++
>   2 files changed, 20 insertions(+)
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index a2abe9a..660792e 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1918,6 +1918,20 @@ static int ufshcd_slave_alloc(struct scsi_device *sdev)
>   }
>   
>   /**
> + * ufshcd_slave_configure - adjust SCSI device configurations
> + * @sdev: pointer to SCSI device
> + */
> +static int ufshcd_slave_configure(struct scsi_device *sdev)
> +{
> +	struct request_queue *q = sdev->request_queue;
> +
> +	blk_queue_update_dma_pad(q, PRDT_DATA_BYTE_COUNT_PAD - 1);
> +	blk_queue_max_segment_size(q, PRDT_DATA_BYTE_COUNT_MAX);
> +
> +	return 0;
> +}
> +
> +/**
>    * ufshcd_slave_destroy - remove SCSI device configurations
>    * @sdev: pointer to SCSI device
>    */
> @@ -2748,6 +2762,7 @@ static struct scsi_host_template ufshcd_driver_template = {
>   	.proc_name		= UFSHCD,
>   	.queuecommand		= ufshcd_queuecommand,
>   	.slave_alloc		= ufshcd_slave_alloc,
> +	.slave_configure	= ufshcd_slave_configure,
>   	.slave_destroy		= ufshcd_slave_destroy,
>   	.eh_abort_handler	= ufshcd_abort,
>   	.eh_device_reset_handler = ufshcd_device_reset,
> diff --git a/drivers/scsi/ufs/ufshci.h b/drivers/scsi/ufs/ufshci.h
> index 0475c66..b2b7004 100644
> --- a/drivers/scsi/ufs/ufshci.h
> +++ b/drivers/scsi/ufs/ufshci.h
> @@ -296,6 +296,11 @@ enum {
>   	MASK_OCS			= 0x0F,
>   };
>   
> +/* The maximum length of the data byte count field in the PRDT is 256KB */
> +#define PRDT_DATA_BYTE_COUNT_MAX	(256 * 1024)
> +/* The granularity of the data byte count field in the PRDT is 32-bit */
> +#define PRDT_DATA_BYTE_COUNT_PAD	4
> +
>   /**
>    * struct ufshcd_sg_entry - UFSHCI PRD Entry
>    * @base_addr: Lower 32bit physical address DW-0