On Mon, Apr 15, 2019 at 11:40 AM Chen-Yu Tsai wens@kernel.org wrote:
On Mon, Apr 15, 2019 at 2:07 PM Jagan Teki jagan@amarulasolutions.com wrote:
On Sun, Feb 10, 2019 at 9:49 PM Andre Przywara andre.przywara@arm.com wrote:
Hi, this is a resend of what I posted some weeks ago, just adding the missing Signed-off-by: in patch 2/3, as pointed out by Philipp. I used the opportunity to add his Reviewed-by: tags on the first two patches. (Many thanks for that!) The rest is unchanged.
Admittedly this is the long way round to solve some nasty SPL code size problem, but it looked beneficial to others as well, so here we go:
arch/arm/include/asm/io.h looks like it's been around since the dawn of time, and was more or less blindly copied from Linux. We don't use and don't need most of the definitions, and mainline Linux got rid of them anyway, so patch 1/3 cleans up this header file to just contain what we need in U-Boot.
Patch 2/3 introduces readl/writel_relaxed accessors, which are cheaper, but more importantly save one (barrier) instruction per accessor. This helps to bring down code size, since especially DRAM controller inits in SPLs tend to do a lot of MMIO.
Consequently patch 3/3 introduces them in the Allwinner H6 DRAM driver, which reduces the SPL size by a whopping 2KB, due to a twist: The AArch64 exception table needs to be 2KB aligned, but we don't do anything special about it the linker script. So depending on where the code before the vectors ends, we have potentially large padding: At the moment this last address is 0x1824 for the H6, so the vectors can only start at 0x2000. By reducing the code size before the vectors by just (at least) 9 instructions, the vectors start at 0x1800 and we save most of the padding.
How come it reduces to 2KB? I can see the diff size of 160 bytes for gcc-6.3.1
₹ aarch64-linux-gnu-size spl/u-boot-spl* text data bss dec hex filename 28376 408 504 29288 7268 spl/u-boot-spl
₹ aarch64-linux-gnu-size spl/u-boot-spl* text data bss dec hex filename 28216 408 504 29128 71c8 spl/u-boot-spl
Because of section alignment issues? I believe Andre is referring to the size of the whole file. Since it gets loaded as a whole, the total size is what matters, not the size of the individual sections.
Well, the input for final sunxi-spl.bin would be u-boot-spl and the above shows the size of file as well 29128 bytes with -160 bytes from 29288.
Since the size of sunxi-spl.bin is truncated to 32K, I couldn't see any difference either.