linux-kernel - USB HDD: Write Cache always shown as Disabled

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Message-ID: <CADDb1s0GF-+TLo00=SvQu=7qxY1DTK0VgSWHd9Vr0=q1k7S2PQ@mail.gmail.com>
Date:	Tue, 27 Sep 2011 17:36:49 +0530
From:	Amit Sahrawat <amit.sahrawat83@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: USB HDD: Write Cache always shown as Disabled

Why is Write Cache always shown as Disabled (Function:
sd_revalidate_disk(), File: drivers/scsi/sd.c)  – even though there is
write cache in USB HDD and which is enabled. This is verified by
enabling/disabling the cached using ‘hdparm’ and then checking the
performance.

I have few USB Hard disks – for all of them it is shown to be

Default Message:
“Assuming drive cache: Write Through”

If I change the condition in sd_read_cache_type(),
if (sdp->skip_ms_page_8){
        //      goto defaults;
}
Sd 0:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn’t
support DPO or FUA.


Can anyone provide any hint to this?  Or am I missing something in this?

Thanks & Regards,
Amit Sahrawat
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