Hi,

On Fri, 2010-12-03 at 13:07 +0000, ext Russell King - ARM Linux wrote:

So please, 2MB, or if you object, at the _very_ _least_ 1MB.  But
definitely not PAGE_SIZE.

Here's a patch for this. Works for me on OMAP3430SDP. If the patch is
ok, I'll send a pull request to Paul.



From 6c54704730626e2683e05574b3cbba966980c956 Mon Sep 17 00:00:00 2001
From: Tomi Valkeinen <redacted>
Date: Tue, 14 Dec 2010 14:16:59 +0200
Subject: [PATCH] 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:

quoted

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 <redacted>
---
 drivers/video/omap2/vram.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/video/omap2/vram.c b/drivers/video/omap2/vram.c
index 2fd7e52..9441e2e 100644
--- a/drivers/video/omap2/vram.c
+++ b/drivers/video/omap2/vram.c

@@ -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);

-- 
1.7.1