Commit 4422c04b authored Dec 14, 2010 by Tomi Valkeinen

OMAP: DSS: VRAM: Align start & size of vram to 2M



Align the start address and size of VRAM area to 2M as per comments from
Russell King:

> > So, why SZ_2M?
>
> Firstly, that's the granularity which we allocate page tables - one
> Linux page table covers 2MB of memory.  We want to avoid creating page
> tables for the main memory mapping as that increases TLB pressure through
> the use of additional TLB entries, and more page table walks.
>
> Plus, we never used to allow the kernel's direct memory mapping to be
> mapped at anything less than section size - this restriction has since
> been lifted due to OMAP SRAM problems, but I'd rather we stuck with it
> to ensure that we have proper behaviour from all parts of the system.
>
> Secondly, we don't want to end up with lots of fragmentation at the end
> of the memory mapping as that'll reduce performance, not only by making
> the pfn_valid() search more expensive.
>
> Emsuring a minimum allocation size and alignment makes sure that the
> regions can be coalesced together into one block, and minimises run-time
> expenses.
>
> So please, 2MB, or if you object, at the _very_ _least_ 1MB.  But
> definitely not PAGE_SIZE.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>
Acked-by: Tony Lindgren <tony@atomide.com>

parent cf7d7e5a

drivers/video/omap2/vram.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -551,7 +551,7 @@ void __init omap_vram_reserve_sdram_memblock(void)
		if (!size)
		return;

		size = PAGE_ALIGN(size);
		size = ALIGN(size, SZ_2M);

		if (paddr) {
		if (paddr & ~PAGE_MASK) {
		@@ -576,7 +576,7 @@ void __init omap_vram_reserve_sdram_memblock(void)
		return;
		}
		} else {
		paddr = memblock_alloc(size, PAGE_SIZE);
		paddr = memblock_alloc(size, SZ_2M);
		}

		memblock_free(paddr, size);