Re: [PATCH][PPC32[NEWBIE] enhancement to virt_to_bus/bus_to_virt (try 2)

[Eugene Surovegin <ebs@ebshome.net>]

On Sun, Dec 05, 2004 at 02:18:45PM -0500, Linh Dang wrote:
> From a single virtual buffer, the DMA library will build a chained list of
> physically contiguous buffers (it  can be one or more physical buffers).
> All the DMA engines I'm familiar with (mpc8260, mpc8580, marvell, etc.)
> accept a list of physical buffers.
> 
> The decoding algorithm (from a single virtual buffer to a chained list of
> physical buffers) is dead simple.

So you gonna call virt_to_bus several times (for each page) and see 
whether you get new phys page or not? This could work, but for the 
common case of phys-continuous buffer it'll be suboptimal, i.e. you 
waste time calling virt_to_bus when it's not needed. TO make it better 
you have to move that range check from virt_to_bus and friends to your 
DMA library, in this case we end up in the same situation we are 
already :) - no need to modify virt_to_bus....

--
Eugene