Re: libata and software reset

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 10/18/22 22:24, John Garry wrote:
> Hi guys,
> 
> In the hisi_sas driver there are times in which we need to issue an ATA
> software reset. For this we use hisi_sas_softreset_ata_disk() ->
> sas_execute_ata_cmd() -> sas_execute_tmf(), which uses libsas "slow
> task" mechanism to issue the command.

Something is wrong here... The reset command sent by that function is
for ATAPI (DEVICE RESET command). There is no device reset command for
SATA disks following the ACS standard.

So hisi_sas_softreset_ata_disk() seems totally bogus to me, unless you
have a CD/DVD drive connected to the HBA :)

This is why the softreset function is a port operation defined by LLDs.
How you reset the device depends on the adapter. E.g., for AHCI, you
need to send a host2device FIS with the software reset bit set.

> 
> I would like if libata provided such a function to issue a software
> reset, such that we can send the command as an ATA queued command.
> 
> The problem is that often when we would want to issue this software
> reset the associated ata port is frozen, like in ATA EH, and so we
> cannot issue ATA queued commands - internal or normal - at that time.
> 
> Is there any way to solve this? Or I am just misunderstanding how and
> when ATA queued commands can and should be used?
> 
> I assume that ata_port_operations.softreset callback requires a method
> to be able to issue the softreset directly from the driver, like
> ahci_softreset() -> ahci_do_softreset() -> ahci_exec_polled_cmd().
> 
> Thanks,
> John

-- 
Damien Le Moal
Western Digital Research