Re: [RFC][PATCH] at91_ide driver

[Stanislaw Gruszka <stf_xl@wp.pl>]

Sunday 01 February 2009 18:13:17 Bartlomiej Zolnierkiewicz napisał(a):
> > I have some doubts about things pointed out by Alan  - atomic access.  
> > Due to flipping 8/16 bit in this driver, all functions accessing task file 
> > and data register should do things atomically. If for example
> > tp_ops->input_data() will be braked by interrupt and any other function
> > accessing task file will be called very bad things can happen.
> 
> All taskfile / data access is atomic, the only exception is [Alt]Status
> register read if shared IRQs are used (which doesn't seem to be the case
> with AT91) or if the hardware is flaky and unexpected IRQs can happen...
> 
> If 8/16-bit flipping is really an issue then AT91 IRQ handler may need
> to save info about current mode on entry, switch to 8-bit (if in 16-bit
> mode), restore the saved mode on exit (if it was 16-bit mode).
I think we don't need it because we don't use shared interrupts.
Moreover hardware allow to Altarnate Status register be accessed
in both 8 and 16 bit modes.

> > If I use IDE_HFLAG_UNMASK_IRQS IDE layer will assure atomic
> > access to ATA registers ?
> 
> IDE_HFLAG_UNMASK_IRQS allows other IRQs to be serviced while IDE IRQ
> is being serviced so really no problem here (unless some other drivers
> also mess with 8/16-bit flipping but if so then the current code needs
> fixing too).
We have exclusive access to Static Memory Controller registers as long
as there are no bug in board specific code. So no problem here either.

Stanislaw Gruszka