[Bug 215447] sr_mod scsi_mode_sense() failure -> "scsi-1 drive"

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https://bugzilla.kernel.org/show_bug.cgi?id=215447

--- Comment #6 from Martin K. Petersen (martin.petersen@oracle.com) ---
Christopher,

> Is anyone able to comment on the sr_mod / cdrom / mptsas issue I'm
> experiencing (see details in bug)?  I fixed my issue with a one line
> patch, but I'd like to know if it's correct and what I should do to
> have it integrated upstream.

My concern is that switching to MODE SENSE(10) by default could break
things for other devices.

There are compelling arguments that we should use MODE SENSE(10). Most
ROM devices appear to favor it. The specs allow both but MMC3 (2001)
mentions MODE SENSE(10) as "shall implement" although it doesn't go as
far as marking it as mandatory in the SCSI command table.

In the current code we fall back to the MODE SENSE(6) command if a MODE
SENSE(10) fails. So if we change the default, unless a device hangs when
we send the 10-byte command, we should be OK.

Another option is to allow a fallback to the 10-byte command if the
6-byte command fails. We currently don't do that because MODE SENSE(6)
was required for so many years. This way we could accommodate devices
such as yours without the risk of changing the default.

The good news is that the "consumer" transports (ATA, FireWire, USB) all
use MODE SENSE(10) by default. So we are really only talking about
changing things for SPI-attached devices which typically are
well-behaved. So my hunch is that switching the default is probably OK,
although I would like the 6/10-byte fallback mechanism to work in both
directions as well.

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