Re: libata and software reset

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

On 10/19/22 14:03, Damien Le Moal wrote:
> 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.

See: ahci_do_softreset() for AHCI.

> 
>>
>> 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