On Fri, Jul 01, 2011 at 06:19:43PM +0200, Arnd Bergmann wrote: > On Friday 01 July 2011, Barry Song wrote: > > It looks like we can new a common function named as of_io_earlymap() > > or something in drivers/of/address.c. of_iomap() does ioremap, > > of_io_earlymap() does early static mapping? > > Then all SoCs can call this function to do early static mapping. if > > so, some lines can be deleted in sirfsoc_of_clk_init(). How do you > > think about newing the function in drivers/of/address.c? > > I think that's a good idea, but the ARM specific implementation cannot > be in common code. Other architectures have stuff similar to iotable_init > in asm/fixmap.h. If we decide on a function prototype for this, the > implementation can be arch/*/.
One of the issues with fixmap is that its based around single pages and indexing an area. It's idiotic to use such a thing if you have to map the ISA memory regions for VGA. Plus, of course, forcing everything down the route of ioremap() and fixmap forces everyone to use 2-level page tables and 4K page table entries, avoiding the possibility of having just a single 1st level page table entry covering their IO space. Not only does it increase TLB pressure but it also makes page table walking more expensive. _______________________________________________ devicetree-discuss mailing list devicetree-discuss@lists.ozlabs.org https://lists.ozlabs.org/listinfo/devicetree-discuss
