Re: libata passthru: support PIO multi commands

From: Mark Lord
Date: Wed Jun 13 2007 - 14:41:23 EST

Albert Lee wrote:
It looks like the ATA passthru commands contain more information than
what libata needs to execute a command.

e.g. protocol number:
libata could possibly infer the protocol from the command opcode.

e.g. multi_count:
libata caches dev->multi_count. Passing multi_count along with
each passthru command looks useless for libata.

e.g. t_dir:
libata could possible infer the direction from the command opcode
or from the protocol number (e.g. 4: PIO_IN / 5: PIO_OUT).

I wonder if the *intent* of the specification was that the low-level driver
should perform whatever setup is necessary to issue the command as given.

So if the command specifies a multcount of 8, then the LLD should issue the
appropriate initialization commands to use a multcount of 8, and then issue
the given R/W MULT command, and then perhaps reset the multcount back to
what it was normally (beforehand) ?

Ditto for the others.

I am *not* proposing that we actually do it this way,
but rather just suggesting a possible rationale.

What does the SAT spec say? Any further hints as to the intent?

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