Re: CVS commit: src/sys/dev/ic

[Jason Thorpe <thorpej%shagadelic.org@localhost>]

On Mar 31, 2010, at 7:45 AM, David Young wrote:

> On Wed, Mar 31, 2010 at 05:09:41AM +0000, Michael Lorenz wrote:
>> Module Name: src
>> Committed By:        macallan
>> Date:                Wed Mar 31 05:09:41 UTC 2010
>> 
>> Modified Files:
>>      src/sys/dev/ic: pcf8584.c
>> 
>> Log Message:
>> Do as OpenSolaris does and read the status register after each write.
>> Now this driver works on my Blade 2500.
> 
> void
> pcfiic_write(struct pcfiic_softc *sc, bus_size_t r, u_int8_t v)
> {
> +       volatile uint8_t junk;
>        bus_space_write_1(sc->sc_iot, sc->sc_ioh, sc->sc_regmap[r], v);
> +       junk = bus_space_read_1(sc->sc_iot, sc->sc_ioh, PCF_S1);
>        bus_space_barrier(sc->sc_iot, sc->sc_ioh, sc->sc_regmap[r], 1,
>            BUS_SPACE_BARRIER_WRITE);
> }
> 
> I wonder, does the device need the read, or is the bus_space_barrier()
> insufficient to flush the write to the device?

bus_space_barrier() doesn't flush ... barriers only enforce the ordering of 
operations (and, of course, with respect to non-overlapping addresses ... 
obviously reads after writes of the same address in code will be enforced on 
the bus without an explicit barrier).

> 
> Dave
> 
> -- 
> David Young             OJC Technologies
> dyoung%ojctech.com@localhost      Urbana, IL * (217) 278-3933

-- thorpej