Re: How to assess PMP register

[Tejun Heo <tj@kernel.org>]

s ticket wrote:
> 2009/5/6 Gwendal Grignou <gwendal@google.com>:
>> - you can not access a PMP device from user space directly because
>> there is no file descriptor for it.
>> - however, libata stores a dump of PMP registers taken after every
>> reset in gscr structure of the ata_device structure that represent the
>> PMP in the kernel. You can modify libata to print the registers you
>> need.
> 
> I add a  `pmp_attach' function ata_port_operation, and call
> `sata_pmp_read' in that
> function. It works fine. But when I call `sata_pmp_read' in process
> context while another
> process is writing to disks, the kernel hangs (deadlock?). Is there
> any suggestion?
> I found that `sata_pmp_read' finally calls `ata_exec_internal_sg' to
> do the real work and
> 'ata_exec_internal_sg' takes ata_port->lock.
> 
> BTW, why `sata_pmp_read' and `sata_pmp_write' aren't exported?

The PMP access functions can only be called from EH context and that's
one of the reasons they aren't exported?  What are you trying to
achieve?

Thanks.

-- 
tejun