On Tue, Mar 18, 2014 at 09:22:50AM +0100, Maxime Ripard wrote:
On Mon, Mar 17, 2014 at 03:33:19PM -0400, Tom Rini wrote:
On Sun, Mar 16, 2014 at 03:19:40PM +0000, Ian Campbell wrote:
On Fri, 2014-03-14 at 15:03 -0400, Tom Rini wrote:
On 03/14/2014 02:50 PM, Hans de Goede wrote:
Hi,
On 03/14/2014 03:17 PM, Tom Rini wrote:
On Fri, Mar 14, 2014 at 10:33:50AM +0000, Ian Campbell wrote:
> Based linux-sunxi#sunxi commit d854c4de2f57 "arm: Handle .gnu.hash section in > ldscripts" vs v2014.01. [snip] > +/* Flat Device Tree (FDT/DT) support */ > +#define CONFIG_OF_LIBFDT > +#define CONFIG_SYS_BOOTMAPSZ (16 << 20)
This seems pretty small. This is to keep things from being relocated into highmem right?
Hmm, this reminds me that we currently need to do a "env set fdt_high ffffffff" in our boot scripts to get ftd to work at all. Would be nice to fix this for upstream. I'm afraid I'm clueless as to why we (sunxi) need it, but we do.
You want to be setting bootm_low (even for bootz, it's about the underlying boot mechanics that bootz and bootelf and ... hook into) to the amount of lowmem the kernel will have. We do this because we do want to make sure that the device tree isn't overwritten by the kernel BSS or similar. Everyone with more DDR than kernel lowmem needs to be doing something along these lines.
So, I'm confused about what to do here ;-)
And I've not made things clearer with a mis-recollection of things. I don't know why I keep saying "bootm_low" when I mean "bootm_size" like I've done in later patches (and thankfully, when poking people on G+).
There's three ways to say "Please ensure that the FDT and if passed initrd do not relocate above a certain location".
- In the environment, set bootm_size to kernel lowmem. This means that
boot_start_lmb restricts the pool used by both fdt and initrd to that value at the top. 2) In the environment, set fdt_high (and if using initrd, initrd_high) to the top of lowmem. This means that we'll make sure they don't get relocated above that value. 3) In the environment set initrd_high to top of lowmem and set bootm_mapsize to lowmem.
In all of the above, lowmem can be replaced with any valid size that's also smaller than lowmem, such as 256MB. Another option, in the environment, is to set initrd_high and fdt_high to 0xffffffff and then relocation is disabled. I would _not_ recommend this in the general case as one of the points of relocation is to ensure we don't get overwritten by the kernel BSS.
IIRC, we added it not to make sure that it was in lowmem, but because we had issues with large enough kernels (multi_v7_defconfig + embedded initramfs) that would overwrite the relocated DTB whenever it was decompressing itself.
Right. The series of problems often goes: 1) Oops, DTB moved into high mem, set fdt_high 0xffffffff to stop that 2) Oops, DTB overwritten by kernel, change fdt load addr.
Which is why relocation is a good thing (at least on the device tree which tends to be small enough to not be a noticable thing) in the default case.