RE: [PATCH V3 01/16] scsi: support well known logical units

["Subhash Jadavani" <subhashj@codeaurora.org>]

Hi Chris,

While testing with another vendor's UFS devices, I realized that SELECT
REPORT need not to be set to 0x02 for making the device report the W-LUs.
Even when SELECT REPORT is set 0x00, this particular UFS device reports the
W-LUs so I looked at the SCSI specification in details and it seems ideally
device should report all the well-known logical units (as it follows the
extended logical unit addressing format) when SELECT REPORT is set 0x00.
Which means one vendor's UFS devices are following SCSI spec for W-LUs
reporting while another vendor's UFS devices don't.

I have reported violation of spec to this other vendor and have also asked
them to fix it. Until they fix their non-standard behavior, we can
workaround their behavior using the device specific quirks in UFS driver
itself.

For now in this patch, we will skip modifying SELECT REPORT field but we
would still require the other part of this patch for fixing the scsi_device
type to wlun (sdev->type = TYPE_WLUN). Hence we will change the commit text
accordingly to reflect the exact purpose of the change.

Regards,
Subhash

-----Original Message-----
From: linux-scsi-owner@vger.kernel.org
[mailto:linux-scsi-owner@vger.kernel.org] On Behalf Of Subhash Jadavani
Sent: Thursday, September 18, 2014 10:18 AM
To: 'Christoph Hellwig'
Cc: 'Dolev Raviv'; James.Bottomley@HansenPartnership.com;
linux-scsi@vger.kernel.org; linux-scsi-owner@vger.kernel.org;
linux-arm-msm@vger.kernel.org; santoshsy@gmail.com; 'Sujit Reddy Thumma';
'Martin K. Petersen'
Subject: RE: [PATCH V3 01/16] scsi: support well known logical units

> If those are the only LUs you specificly need I'd suggest you just
manually call scsi_add_device from your driver for those instead of listing
them in REPORT_LUNS and making them part of the normal LUN scan. 

Yes, we can do that but not sure what would be advantage of making the LLDs
to add these ad-hoc hooks instead of scsi_scan handle it on its own and
leaving the LLDs from adding them explicitly? Do you foresee any issues
(other than few extra scsi_device instances which may not be useful all scsi
devices) with scsi_scan scanning all the LUs (including well known LUs)?

Regards,
Subhash

-----Original Message-----
From: linux-scsi-owner@vger.kernel.org
[mailto:linux-scsi-owner@vger.kernel.org] On Behalf Of 'Christoph Hellwig'
Sent: Saturday, September 13, 2014 11:55 AM
To: Subhash Jadavani
Cc: 'Christoph Hellwig'; 'Dolev Raviv';
James.Bottomley@HansenPartnership.com; linux-scsi@vger.kernel.org;
linux-scsi-owner@vger.kernel.org; linux-arm-msm@vger.kernel.org;
santoshsy@gmail.com; 'Sujit Reddy Thumma'; 'Martin K. Petersen'
Subject: Re: [PATCH V3 01/16] scsi: support well known logical units

On Thu, Sep 11, 2014 at 05:41:18PM -0700, Subhash Jadavani wrote:
> 
> UFS device has supports 4 different well known logical units:
"REPORT_LUNS"
> (address: 01h), "UFS Device" (address: 50h), "RPMB" (address: 44h) and 
> "BOOT" (address: 30h).
> 
> UFS device's power management needs to be controlled by "POWER CONDITION"
> field of SSU (START STOP UNIT) command. But this "power condition"  
> field will take effect only when its sent to "UFS device" well known 
> logical unit
> (address: 50h) hence we require the scsi_device instance to represent 
> this logical unit in order for the UFS host driver to send the SSU 
> command for power management.
> 
> We also require the scsi_device instance for "RPMB" (Replay Protected 
> Memory
> Block) LU so user space process can control this LU.

If those are the only LUs you specificly need I'd suggest you just manually
call scsi_add_device from your driver for those instead of listing them in
REPORT_LUNS and making them part of the normal LUN scan.  One advantage of
the well known LUNs is that you always know where in the LUN namespace they
are :)

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