Re: Discussion about iopa()

Li Yang-r58472 wrote:

Do you think we should remove iopa?

It's not used very much any more.  If you do a grep of the code, I think 
only some legacy drivers use it.

As long as ioremap'd memory is both physically and virtually contiguous, 
I think iopa() is unnecessary.

The information is often not so obvious.  The most case of using iopa is
that we allocate memory from MURAM using rheap, and then get the
physical address of it.  We can calculate phy_addr by using:  virt_addr
- virt_muram_base + phy_muram_base, but it is not as straightforward as
just using the page table, let alone we need to keep track of
virt_muram_base and phy_muram_base.

Walking the page table is slower than using pointer math, so you want to 
avoid iopa() if you can.

I think in general, the driver that calls ioremap() should store the 
physical address along with the virtual address of the base pointer.