Tejun Heo wrote:

libata doesn't really put much restrictions on what a LLD should do on
entering EH and if the controller's behavior is predictable, there's no
reason to freeze the port.  If the problem is that the DMA engine isn't
usable after PMP error but it's known that the controller isn't gonna
cause irq storm, no need to freeze.  The only command EH issues before
resetting which can use DMA protocol is READ_LOG_EXT.  Maybe there needs
to be a way to force PIO protocol for READ_LOG_EXT.  Other than that, if
no-data and PIO-only commands work fine, EH autopsy should work fine.

..

Eh?  READ LOG EXT *is* a PIO command, as opposed to READ LOG DMA EXT
which uses DMA.

And the EH also issues PIO READ_BUFFER commands for PM ports, if a PM is present.

???