Re: [PATCH RFC v3 2/7] ata: libata-scsi: Add ata_internal_queuecommand()

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

On 10/27/22 18:56, John Garry wrote:
> On 27/10/2022 02:45, Damien Le Moal wrote:
>> On 10/25/22 19:32, John Garry wrote:
>>> Add callback to queue reserved commands - call it "internal" as this is
>>> what libata uses.
>>>
>>> Also add it to the base ATA SHT.
>>>
>>> Signed-off-by: John Garry <john.garry@huawei.com>
>>> ---
>>>   drivers/ata/libata-scsi.c | 14 ++++++++++++++
>>>   include/linux/libata.h    |  5 ++++-
>>>   2 files changed, 18 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
>>> index 30d7c90b0c35..0d6f37d80137 100644
>>> --- a/drivers/ata/libata-scsi.c
>>> +++ b/drivers/ata/libata-scsi.c
>>> @@ -1118,6 +1118,20 @@ int ata_scsi_dev_config(struct scsi_device *sdev, struct ata_device *dev)
>>>   	return 0;
>>>   }
>>>   
>>> +int ata_internal_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmd)
>>> +{
>>> +	struct ata_port *ap;
>>> +	int res;
>>> +
>>> +	ap = ata_shost_to_port(shost);
>>
>> You can have this initialization together with the ap declaration.
>>
>>> +	spin_lock_irq(ap->lock);
>>> +	res = ata_sas_queuecmd(scmd, ap);
>>> +	spin_unlock_irq(ap->lock);
>>> +
>>> +	return res;
>>> +}
>>> +EXPORT_SYMBOL_GPL(ata_internal_queuecommand);
>>
>> I am officially lost here. Do not see why this function is needed...
> 
> The general idea in this series is to send ATA internal commands as 
> requests. And this function is used as the SCSI midlayer to queue 
> reserved commands. See how it is plugged into __ATA_BASE_SHT, below.
> 
> So we have this overall flow:
> 
> ata_exec_internal_sg():
>   -> alloc request
>   -> blk_execute_rq_nowait()
>       ... -> scsi_queue_rq()
> 		-> sht->reserved_queuecommd()
> 			-> ata_internal_queuecommand()
> 
> And then we have ata_internal_queuecommand() -> ata_sas_queuecmd() -> 
> ata_scsi_queue_internal() -> ata_qc_issue().
> 
> Hope it makes sense.

OK. Got it.
However, ata_exec_internal_sg() being used only from EH context with the
queue quiesced, will blk_execute_rq_nowait() work ? Is there an exception
for internal reserved tags ?

> 
> Thanks,
> John
> 
>>
>>> +
>>>   /**
>>>    *	ata_scsi_slave_config - Set SCSI device attributes
>>>    *	@sdev: SCSI device to examine
>>> diff --git a/include/linux/libata.h b/include/linux/libata.h
>>> index 8938b584520f..f09c5dca16ce 100644
>>> --- a/include/linux/libata.h
>>> +++ b/include/linux/libata.h
>>> @@ -1141,6 +1141,8 @@ extern int ata_std_bios_param(struct scsi_device *sdev,
>>>   			      sector_t capacity, int geom[]);
>>>   extern void ata_scsi_unlock_native_capacity(struct scsi_device *sdev);
>>>   extern int ata_scsi_slave_config(struct scsi_device *sdev);
>>> +extern int ata_internal_queuecommand(struct Scsi_Host *shost,
>>> +				struct scsi_cmnd *scmd);
>>>   extern void ata_scsi_slave_destroy(struct scsi_device *sdev);
>>>   extern int ata_scsi_change_queue_depth(struct scsi_device *sdev,
>>>   				       int queue_depth);
>>> @@ -1391,7 +1393,8 @@ extern const struct attribute_group *ata_common_sdev_groups[];
>>>   	.slave_destroy		= ata_scsi_slave_destroy,	\
>>>   	.bios_param		= ata_std_bios_param,		\
>>>   	.unlock_native_capacity	= ata_scsi_unlock_native_capacity,\
>>> -	.max_sectors		= ATA_MAX_SECTORS_LBA48
>>> +	.max_sectors		= ATA_MAX_SECTORS_LBA48,\
>>> +	.reserved_queuecommand = ata_internal_queuecommand
>>>   
>>>   #define ATA_SUBBASE_SHT(drv_name)				\
>>>   	__ATA_BASE_SHT(drv_name),				\
>>
> 

-- 
Damien Le Moal
Western Digital Research