On Fri, 20 Feb 2015 10:19:51 +0100 Hans de Goede hdegoede@redhat.com wrote:
Hi,
On 20-02-15 09:08, Siarhei Siamashka wrote:
Store the 'compatibility revision' number in the top 4 bits of the machine id and pass it to the kernel. The old buggy kernels will fail to load with a very much googlable error message on the serial console:
"Error: unrecognized/unsupported machine ID (r1 = 0x100010bb)"
This error message can be documented in the linux-sunxi wiki with proper explanations about how to resolve this situation and where to get the necessary bugfixes for the sunxi-3.4 kernel.
The fixed sunxi-3.4 kernels can implement a revision compatibility check and clear the top 4 bits of the machine id if everything is alright.
Signed-off-by: Siarhei Siamashka siarhei.siamashka@gmail.com
TBH I'm not a big fan if this.
To be used together with: https://groups.google.com/forum/#!topic/linux-sunxi/LOAxP3kAYs8
Nor of this one.
What I would prefer is for CONFIG_OLD_SUNXI_KERNEL_COMPAT to go away
Yes, the CONFIG_OLD_SUNXI_KERNEL_COMPAT option is barely useful for anything right now. And it would be great to get rid of it.
and for u-boot to automatically do the right thing when booting an old kernel.
Sure, but first we need to define what is the "right thing".
Recently some patches where merged to make "bootm" work without an fdt even when build with fdt support.
Specifically in common/image-fdt.c line 437 there is:
if (!select && ok_no_fdt) { debug("Continuing to boot without FDT\n"); return 0; }So we known when executing the bootm command that we do not have an fdt.
If this is the case, and only when this (no fdt) is the case then in arch/arm/lib/bootm.c: boot_prep_linux()
The board specific setup_board_tags() function gets called, we could define our own version of this (it has an empty weak default), and in our own version fixup things for the old kernel to just work.
Sounds like we are coming back to
http://lists.denx.de/pipermail/u-boot/2014-October/191697.html
As you may guess, I'm in favour of having everything working automatically without the need to set extra Kconfig options or environment variables :-)
That means:
Halving PLL5, then waiting for it to settle, then reprogramming the DRAM clk divider, I'm assuming that this will work if done in this order, but we obviously need to test this thoroughly.
Halving PLL6, then waiting for it to settle, then reprogram the MBUS divider, and check and update mmc mod clock dividers.
This already looks somewhat more complicated than necessary...
Modifying armv7_boot_nonsec so that we can override the default. We can do this e.g. by adding a global armv7_boot_nonsec_default variable and setting that from setup_board_tags().
This way we can just do the right thing automatically,
By the "right thing", do you mean booting the sunxi-3.4 kernel with weird PLL5 and PLL6 settings just because some *older* versions of this kernel used to have bugs in the past?
and this has the added advantage that if we later find out that we're doing something in u-boot which is not good for the older kernels we can fix it in u-boot without needing to coordinate with the sunxi-3.4 kernels. In my experience the version check for compatibility style solution you are proposing brings a large maintenance burden,
I don't expect any maintenance burden at all. We only ever need this coordination to take care of very serious showstopper bugs. And such bugs have been already fixed.
We probably might only need an update for this version check if we try to adjust AXP152 DCDC4 voltage on A10s (and the sunxi-3.4 kernel would need to be patched in order not to touch DCDC4). Or if some other critical compatibility problem gets reported.
Please note that the newly discovered PLL6 issue is not a critical one and does not even deserve any coordination or version bump at all. It only causes some performance drop (MBUS clock speed reduction from 204 MHz to 150 MHz) and is easy to workaround in other ways.
and it does not actually help the user, as the users wants something which just works.
And the users do have something that just works.
The only problem here is poor errors reporting. Tsvetan and Lars wasted some of their time doing debugging simply because they picked a wrong kernel. If they had a sane error message right from the start, then they would have just switched to a different kernel and be good. Or cherry picked the important fixes in the case of working with a heavily diverged sunxi-3.4 fork.
Tsvetan, Lars: do you have any comments on this?