Mathieu Fluhr wrote:
On Wed, 2007-10-17 at 21:31 -0400, Jeff Garzik wrote:
Robert Hancock wrote:
This doesn't seem a very reliable way to identify an IDE device, as all
that 0 means is that the device does not claim conformance to any
standard. I would think it would be legitimate for an IDE device to put
a value like 5 in there as well, if it complies with SPC-4..
Via the this-doesnt-really-matter-but-it-should-be-noted department:
According to the latest on t10.org, MMC retroactively permitted SCSI
version to be zero, for MMC-compliant USB and ATAPI devices.
Quoting to the latest MtFuji draft (Section 17.7.1):
"The ANSI Version field shall contain a non-zero value to comply with
this version of the Specification for a SCSI logical unit or zero for
an ATAPI logical unit."
In the case of libata though, that appears to be due to this code in
drivers/ata/libata-scsi.c:
/* ATAPI devices typically report zero for their SCSI version,
* and sometimes deviate from the spec WRT response data
* format. If SCSI version is reported as zero like normal,
* then we make the following fixups: 1) Fake MMC-5 version,
* to indicate to the Linux scsi midlayer this is a modern
* device. 2) Ensure response data format / ATAPI information
* are always correct.
*/
if (buf[2] == 0) {
buf[2] = 0x5;
buf[3] = 0x32;
}
This explain a lot... But (Sorry I am not a scsi mid-layer expert) why
faking what the device outputs?
The SCSI midlayer makes a lot of "if scsi version <= 2" choices. In the
case of ATAPI, we do not want to force ATAPI down the path of ancient
SCSI devices, as this disables some MMC features that modern ATAPI
devices support.
Jeff
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