Re: [PROPOSED] ata: Report 16/32bit PIO as best we can

[Jeff Garzik <jeff@garzik.org>]

Alan Cox wrote:
>> With the attached patch, you can use ->flags for the two new flags, and 
>> you can set those bits in the driver where you set the other 
>> ATA_FLAG_xxx bits.
> 
> Its half way but I realised there is another reason that doesn't work
> (and indeed why the device private flags are asking for trouble)
> 
> What are the locking sematics for ap->flags ?

In general, for both driver-private flags and ATA_FLAG_xxx, the flags 
should be set at compile or pci_driver::probe() time, and never touched 
after that.

So your patch is a bit of abuse, really, by fiddling with ap->flags at 
all ;-)  The drivers, for example, never touch the driver-private flags 
after they are set at init.  The core will occasionally twiddle flags, 
inside of spin_lock_irqsave(ap->lock)

Since they are legacy ioctls, I think that reflecting current reality 
should be sufficient.  That is what the current set does:

	* GET: return "16 bit"
	* SET: if "16 bit" return success else fail

Thus 'set' has always been an illusion for libata.  It's really been 
read-only.

	Jeff