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Date:      Fri, 22 Nov 2002 22:52:26 -0700
From:      "Kenneth D. Merry" <ken@kdm.org>
To:        scsi@FreeBSD.org
Cc:        stable@FreeBSD.org
Subject:   call for testers: cd(4) mode sense/mode select patches
Message-ID:  <20021122225225.A65816@panzer.kdm.org>

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Here are patches against -current and -stable to add automatic detection of
CDROM drives that can't handle 6 byte mode sense and mode select:

http://people.FreeBSD.org/~ken/scsi_cd.cmdsize.20021122
http://people.FreeBSD.org/~ken/scsi_cd.cmdsize.stable.20021122

These new patches fix a data corruption bug in the last set that would
likely cause a panic.

These patches also change the way the da(4) driver handles the no_6_byte
sysctl.  There is now a per-drive sysctl to set the minimum command size
for that particular disk.  (Since you could have multiple disks with
multiple requirements in one system.)

I have also added loader tunable support for all the sysctls in the da(4)
and cd(4) drivers.

Finally, I've disabled MODE_SENSE and MODE_SELECT translation in ATAPICAM
in both -current and -stable, and in the umass(4) driver in -current, since
there's no way for that to work properly (see below).  (Translation hasn't
been MFCed for umass(4) yet, thus the reason I didn't change it in -stable.)

I'd appreciate it if folks could test this, especially people with CDROM
drives running via usb, firewire, or ATAPICAM, but also people with older
SCSI CDROM drives.

To test this, apply the patch (for -current or -stable as appropriate) and
do the following:

cdcontrol status
cdcontrol info
cdcontrol play  (make sure audio comes out)
cdcontrol next  (make sure it skips to the next track here)

If you get an error in response to 'cdcontrol next', definitely let me know
what kind of drive you have (dmesg is fine) and how it is hooked up (SCSI,
firewire, ATAPICAM, usb, etc.).  The SCSI-2 PLAY_TRACK command has
apparantly been deprecated in the MMC specs, so some drives don't support
it.  I'd like to get a handle on which ones do and don't, if possible.
(The work around isn't hard, but isn't in this patch.)

Reports of success or failure are welcome.

=======

Now for more details....

When we get an illegal request in response to a 6 byte mode sense or mode
select, we reformat the command to be a 10-byte mode sense or mode select
and reissue it.

These patches also work with drives that do not return block descriptors
(even when dbd is 0 in the mode sense command), and drives that return
multiple block descriptors.  (They work better with the former than the
latter; with the latter, they mostly just bail out.)

While commands like READ(6) and WRITE(6) can be translated down in the SIM
driver, like the ATAPICAM and usb code do, MODE_SENSE(6) and MODE_SELECT(6)
cannot be translated, because the 10-byte version of the parameter list is
longer.

This means that when, e.g., a MODE_SENSE(6) command is translated to a
MODE_SENSE(10) command, the page will likely be truncated (unless more
space is allocated than needed), and since the peripheral driver code isn't
expecting the returned data to be in MODE_SENSE(10) format, it'll be
looking in the wrong place for the mode page.

The SIM drivers have no way of knowing how long the buffer is that they've
been given for a mode sense or mode select, so they can't just up the
dxfer_len, change the CDB and call it good.

The only way to do translation effectively for these two commands is where
the buffer was originally allocated -- in the peripheral driver.

So I have implemented translation and 10-byte mode sense and mode select
for the cd(4) driver.  Why do translation?  Why not just default to 10-byte
commands?  Because some SCSI CDROM drives, maybe quite a few, don't support
10 byte mode sense and mode select.  (The 8x Plextor in my test box
doesn't, for example.)

The right way to do this, eventually, is with the CAM_NEW_TRAN_CODE.
6byte/10byte can be a function of the protocol, and we can hopefully select
the right size command up front.  It will take a lot of infrastructure
work to make it happen, but that functionality will hopefully solve several
problems.

Since translation won't work at the SIM level, I have disabled
MODE_SENSE(6) and MODE_SELECT translation in ATAPICAM and umass(4).

Comments are welcome on the patches; they're more complicated than I would
like, but unfortunately that complication seems necessary to get the
desired functionality.

Many thanks to David Kleiner <kleiner@panix.com> for testing multiple
iterations of these patches, he has been a big help.

Ken
-- 
Kenneth Merry
ken@kdm.org

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