Accessing flash directly from User Space [SOLVED]

[Segher Boessenkool]

>>>> mmio[0] = address;
>>>> mmio[1] = data;
>>>> mb();

eieio is enough here.

>>>> mmio[3] |= 0x01; /* This triggers an operation -> address=data */
>>>> /* probably also need an mb() here, if the following code
>>>>  * depends on the operation to be triggered. */

No, a sync does not guarantee the device has seen the store yet;
you need something specific to the device to guarantee this.
Usually a load (from the same register!) followed by code that
makes sure the load has finished is sufficient (and necessary).

>>> hmm, the mmio[0] and mmio[1] are written in order I hope?
>>
>> We do not care in this example, as the write to [3] does trigger
>> the device operation. We do only care that [0] and [1] are set
>> when [3] is written. We do not care in what order [0] and [1] are  
>> written.
>
> In this example yes, I was wondering in general.

The writes will not be reordered, but they can be combined,
unless you put an eieio (or sync) inbetween.

> So what does guarded memory mapping on ppc mean really? If I need
> that much mb(), guarded does not seem to do much.

Loosely speaking, guarded means no prefetch is done.


Segher