Re: [PATCH] make ata_exec_internal_sg honor DMADIR

[Tejun Heo <tj@kernel.org>]

Hello,

On Mon, May 20, 2013 at 12:51:20PM +0200, Vincent Pelletier wrote:
> Putting the knob on the port is just a way I thought about to hold the 
> configuration before the drive is plugged into the system (because so far I 
> was focussed on host-side being hot-pluggable, I indeed didn't consider the 
> opposite situation) so it can be used before libata tries to access the 
> device.

Right, we don't even have the sysfs node before probing.  I forgot
about that.

> So it would be something like:
> - plug device (or boot up)
>   -> detection times out, device "half" configured (sysfs node present, drive
>      not usable)
> - cd $DEVICE_IN_SYSFS
> - echo 1 > atapi_dmadir
> - echo 1 > (rescan|reinit|...)
> 
> If it's ok, I'll write a patch to add a rescan write-only file (will also be 
> independent from the 2 other patches).

Ugh... so, this is inherently racy between the probing code and admin.
Maybe we should just implement a new libata.force param and forget
about dynamic configuration?

One more thing.  In the ata_exec_internal_sg(), DMADIR should be set
iff DMA is being used, right?  So, it should also check tf->protocol.
It prolly should test tf->protocol == ATAPI_PROT_DMA instead of cdb.

Thanks.

-- 
tejun