linux-kernel - Re: [PATCH v3 1/5] scsi: Adjust DBD setting in mode sense for caching mode page per LLD

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Date:   Tue, 12 Nov 2019 22:03:52 -0500
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Can Guo <cang@...eaurora.org>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-kernel@...r.kernel.org (open list)
Subject: Re: [PATCH v3 1/5] scsi: Adjust DBD setting in mode sense for caching mode page per LLD

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