linux-kernel - Re: [PATCH v2 1/5] scsi: Adjust DBD setting in mode sense for caching mode page per LLD

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Message-ID: <fd78538f-8e5f-2e5f-0107-a8bc284d037d@android.com>
Date:   Thu, 31 Oct 2019 08:20:58 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Can Guo <cang@...eaurora.org>, asutoshd@...eaurora.org,
        nguyenb@...eaurora.org, rnayak@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.com
Cc:     "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] scsi: Adjust DBD setting in mode sense for caching
 mode page per LLD

On 10/28/19 8:10 PM, Can Guo wrote:
> Host sends MODE_SENSE_10 with caching mode page, to check if the device
> supports the cache feature.
> UFS JEDEC standards require DBD field to be set to 1.
>
> This patch allows LLD to define the setting of DBD if required.
>
> Signed-off-by: Can Guo <cang@...eaurora.org>
> ---
>   drivers/scsi/sd.c        | 6 +++++-
>   include/scsi/scsi_host.h | 6 ++++++
>   2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index aab4ed8..6d8194f 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -2629,6 +2629,7 @@ static int sd_try_rc16_first(struct scsi_device *sdp)
>   {
>   	int len = 0, res;
>   	struct scsi_device *sdp = sdkp->device;
> +	struct Scsi_Host *host = sdp->host;
variable locality
>   	int dbd;
>   	int modepage;
> @@ -2660,7 +2661,10 @@ static int sd_try_rc16_first(struct scsi_device *sdp)
>   		dbd = 8;
>   	} else {
>   		modepage = 8;
> -		dbd = 0;
> +		if (host->set_dbd_for_caching)
> +			dbd = 8;
> +		else
> +			dbd = 0;
>   	}
>   

This simplifies to:

-   } else if (sdp->type == TYPE_RBC) {

+    } else if (sdp->type == TYPE_RBC || sdp->host->set_dbd_for_caching) {

>   	/* cautiously ask */
> diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> index 2c3f0c5..3900987 100644
> --- a/include/scsi/scsi_host.h
> +++ b/include/scsi/scsi_host.h
> @@ -650,6 +650,12 @@ struct Scsi_Host {
>   	unsigned no_scsi2_lun_in_cdb:1;
>   
>   	/*
> +	 * Set "DBD" field in mode_sense caching mode page in case it is
> +	 * mandatory by LLD standard.
> +	 */
> +	unsigned set_dbd_for_caching:1;
> +
> +	/*
>   	 * Optional work queue to be utilized by the transport
>   	 */
>   	char work_q_name[20];