On Sun, Jan 10, 2021 at 05:20:50PM +0100, Heinrich Schuchardt wrote:
On 1/10/21 2:43 PM, Tom Rini wrote:
On Sun, Jan 10, 2021 at 01:05:14PM +0100, Heinrich Schuchardt wrote:
On 1/9/21 10:23 PM, Tom Rini wrote:
On Sat, Jan 09, 2021 at 08:59:01PM +0100, Heinrich Schuchardt wrote:
Am 9. Januar 2021 20:40:04 MEZ schrieb Tom Rini trini@konsulko.com:
On Sat, Jan 09, 2021 at 08:33:40PM +0100, Heinrich Schuchardt wrote: > On 1/9/21 7:58 PM, Tom Rini wrote: > > On Sat, Jan 09, 2021 at 08:47:07PM +0200, Andy Shevchenko wrote: > > > On Sat, Jan 9, 2021 at 8:06 PM Heinrich Schuchardt xypron.glpk@gmx.de wrote: > > > > > > > > The comment for initrd_high in the coding and in README were contradicting > > > > and neither fully described what the coding does. > > > > > > > > Clarify the usage of the special value ~0UL for the environment variable > > > > initrd_high. > > > > > > All those F:s are hard to read in the comments and documentation and > > > typo prone. I would prefer to rephrase like "all 1:s value in 32- or > > > 64-bit format" or alike. > > > > If we're going to improve this we should also note it's discouraged > > unless you know for certain there will be no overlap and it's strongly > > discouraged in default environments. > > What exactly is discouraged? > > * setting initrd_high to a value != ~0? Here I would agree. > * setting intird_high to ~0? Why should we copy initrd to a > different place? Is it for some outdated Linux release?
We should always default to allowing the initrd to be relocated because we can see (in many cases) overlap that will lead to failure to boot but this forces us to ignore that. Having good default load values means we don't have a problem here.
We have an initrd that is already in memory. What could it overlap with that is not already overwritten?
Having the kernel and initrd too close in memory has the kernel BSS overwrite the initrd. This has happened time and time again before I went around making some platforms have reasonable (ie kernel early, ramdisk in lowmem but beyond where a kernel+bss can be, etc) defaults and pushing others to do the same.
Can you provide the text you want to see here?
Off-hand, it should look more like the big comment block in include/configs/ti_armv7_common.h and reference the Linux booting on arm/arm64 documents while noting that other architectures have the same fundamental issues and their exact limits may or may not be as well documented.
There is nothing in the include/configs/ti_armv7_common.h comments requiring to relocate initrd.
/*
- We setup defaults based on constraints from the Linux kernel, which should
- also be safe elsewhere. We have the default load at 32MB into DDR (for
- the kernel), FDT above 128MB (the maximum location for the end of the
- kernel), and the ramdisk 512KB above that (allowing for hopefully never
- seen large trees). We say all of this must be within the first 256MB
- as that will normally be within the kernel lowmem and thus visible via
- bootm_size and we only run on platforms with 256MB or more of memory.
- As a temporary storage for DTBO blobs (which should be applied into DTB
- blob), we use the location 15.5 MB above the ramdisk. If someone wants to
- use ramdisk bigger than 15.5 MB, then DTBO can be loaded and applied to DTB
- blob before loading the ramdisk, as DTBO location is only used as a temporary
- storage, and can be re-used after 'fdt apply' command is done.
*/
I cannot see how this relates to initrd relocation.
You cannot safely disable initrd relocation without ensuring it won't be locked in an unsafe location first. It's also _generally_ going to be noise in the boot sequence and not an advisable default. It should be documented as part of how to tune a system for optimal boot times. But given how often defaults are copy/pasted to the next platform without fully understanding why those values were picked is why what we use as default in one platform needs to be very carefully done.