Tejun Heo wrote:
Jeff Garzik wrote:
Mark Lord wrote:
For example, I think all existing ATAPI drives only speak 12-byte packet
protocols, and so if we tell SCSI we're good for 16-byte, then won't the
SCSI layer suddenly start sending us READ_16 and the like?
Speaking strictly about the device, IDENTIFY PACKET DEVICE data page
tells us whether the device supports 12-byte or 16-byte CDBs. No need
to guess.
Some host controllers only support 12-byte, but I think that most should
support 16-byte.
Out of curiosity, does ATA controllers which don't allow 16byte CDB
actually exist? It's transferred using PIO protocol anyway.
That's why I think that most PATA controllers are likely safe, since it
is just more "twiddling signals" directly to the device.
We have to be more careful, ironically, with the "smart" controllers.
They are more likely to keep the CDB contents in a FIFO or other silicon
buffer somewhere, as temporary storage during a DMA -> buffer -> device
transfer of the CDB contents.
Any first-gen SATA-emulating-PATA controller is instantly under
suspicion, because they are not truly "twiddling signals" but emulating
such by building FIS's under the hood.
Jeff
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