Re: How to write portable MMIO code?

In article <[e-mail]> you wrote:
>>   - should one in general (i.e., assuming the worst case) do wmb() on 
>> writes, and mb() on reads?

readl() and writel() are specified to contain the proper barriers already.

 
> I don't think mb() will help you. You're probably experiencing PCI posting 
> problems - when a writel() has executed, that doesn't necessarily mean 
> that the transaction has actually happened it may (and will) be buffered 
> for a potentially long time.
> 
> However, PCI won't reorder reads vs. writes, so you when you want to be 
> sure that a write() actually reached the hardware, do a dummy read() 
> afterwards, that'll flush the write buffer.

yup