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Date:   Fri, 18 May 2018 16:35:17 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Alexander Kappner <agk@godking.net>
cc:     Oliver Neukum <oneukum@suse.com>, <gregkh@linuxfoundation.org>,
        <usb-storage@lists.one-eyed-alien.net>,
        <linux-kernel@vger.kernel.org>, <linux-usb@vger.kernel.org>
Subject: Re: [PATCH] usb-storage: Add quirks to make G-Technology "G-Drive"
 work
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On Fri, 18 May 2018, Alexander Kappner wrote:

> Further debugging shows that the code that causes the device to hang is in 
> drivers/scsi/sd.c:2698. So the reason why usb-storage works and UAS does 
> not is because the device setting both skip_ms_page_3f=1 and 
> skip_ms_page_8=1 is required. The US_FL_NO_WP_DETECT flag does the former, 
> and usb-storage (but not UAS) by default does the latter 
> (drivers/usb/storage/scsiglue.c:198):
> 
>  /*
>                  * A number of devices have problems with MODE SENSE for
>                  * page x08, so we will skip it.
>                  */
>                 sdev->skip_ms_page_8 = 1;
> 
> 
> Forcing both skip_ms_page_3f and skip_ms_page_8 to 1 results in UAS and 
> usb-storage working. Oliver's code only set skip_ms_page_3f. 

Good detective work!

> Do we want a patch to introduce a quirk flag for skip_ms_page_8,  similar to 
> the US_FL_NO_WP_DETECT quirk bit for skip_ms_page_3f? This may even resolve 
> the issues with other devices in unusual_uas.h that currently have all UAS 
> support disabled. I'd be happy to write the patch, but I'm not sure we want 
> to reserve a quirk bit for what's currently only a single device known to 
> have this issue.  Please advise. 

Yes, I think we want a patch.  Unless Oliver disagrees, please go ahead 
and prepare one.

Alan Stern