Re: [PATCH/RFC 3/4] libata: interrupt driven pio for libata-core

[Albert Lee <albertcc@tw.ibm.com>]

Hi Bart,:

>
>>When the state is HSM_ST_FIRST,  ata_host_intr() checks the
>>(qc->dev->flags & ATA_DFLAG_CDB_INTR) flag.
>>Also in atapi_packet_task(), the host lock is aquired during the state
>>transition from HSM_ST_FIRST to next state.
>>So, the race between the irq handler and atapi_packet_task() is avoided.
>>    
>>
>
>What about ATAPI device with !dev->flags & ATA_DFLAG_CDB_INTR)?
>
>Shouldn't we do spin_lock_irqsave() in atapi_packet_task() before
>actually touching hardware?
>
>  
>
For the ATAPI devices that don't raise CDB interrupes,
when atapi_packet_task() is entered, the state is HSM_ST_FIRST.
 In this state, the irq handler will check the ATA_DFLAG_CDB_INTR flag 
and skip touching the hardware.
atapi_packet_task() is safe to read the device status register at this 
state.
atapi_packet_task() does spin_lock_irqsave() when changing the states 
from HSM_ST_FIRST to say, HSM_ST and sending out the data.

For the ATAPI devices that raise CDB interrupes,
ata_qc_issue_prot() won't queue an new atapi_packet_task().
The irq handler takes over after ata_qc_issue_prot() and can touch the 
hardware.

Thanks for the comments,

Albert