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To:     Can Guo <cang@codeaurora.org>
Cc:     asutoshd@codeaurora.org, nguyenb@codeaurora.org,
        rnayak@codeaurora.org, linux-scsi@vger.kernel.org,
        kernel-team@android.com, saravanak@google.com, salyzyn@google.com,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-kernel@vger.kernel.org (open list)
Subject: Re: [PATCH v3 1/5] scsi: Adjust DBD setting in mode sense for caching mode page per LLD
From:   "Martin K. Petersen" <martin.petersen@oracle.com>
Organization: Oracle Corporation
References: <1572670898-750-1-git-send-email-cang@codeaurora.org>
        <1572670898-750-2-git-send-email-cang@codeaurora.org>
Date:   Tue, 12 Nov 2019 22:03:52 -0500
In-Reply-To: <1572670898-750-2-git-send-email-cang@codeaurora.org> (Can Guo's
        message of "Fri, 1 Nov 2019 22:01:34 -0700")
Message-ID: <yq1tv78pjdz.fsf@oracle.com>
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Can,

> 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.

UFS requires DBD for all MODE SENSE(10) invocations, not just for
accessing the caching mode page. I think the flag name needs to reflect
this.

Also, I do not particularly like this being a scsi_host flag. All the
other flags we have in this department are per scsi_device.

My recommendation would be to add a set_dbd_for_ms flag to struct
scsi_device and then do:

	sdev->set_dbd_for_ms = 1;

in ufshcd_slave_alloc() mirroring the existing:

        sdev->use_10_for_ms = 1;

This makes the MODE SENSE tweakery consistent.

Thanks!

-- 
Martin K. Petersen	Oracle Linux Engineering