On Sat, 2015-02-21 at 07:34 +0200, Siarhei Siamashka wrote: > Right now U-Boot supports the CONFIG_OLD_SUNXI_KERNEL_COMPAT option, > which makes it go out of its way in limiting the selection of PLL clock > frequencies and PMIC voltages in order not to upset outdated buggy > sunxi-3.4 kernel releases. And if the CONFIG_OLD_SUNXI_KERNEL_COMPAT > option is not set, then booting such old kernels exhibits various > failures at runtime. This is very user unfriendly, and there were > already several incidents when people wasted their time being hit > by these runtime failures and trying to debug them. > > The right solution is not to add hacks and workarounds to the mainline > U-Boot, but to fix these bugs in the sunxi-3.4 kernel. And in fact, > the updated sunxi-3.4 kernels already exist. Still we need to follow > the 'Principle of Least Surprise' and U-Boot needs to ensure that > the old buggy kernels are not getting happily booted when the > CONFIG_OLD_SUNXI_KERNEL_COMPAT option is not set. And this patch > addresses this particular issue. > > This patch makes U-Boot 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 (the "r1 = 0x100010bb" part of it): > > "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 implement a revision compatibility check > and clear the top 4 bits of the machine id if everything is alright. > By accepting the machine id with the bits 31:28 set to 1, the sunxi-3.4 > kernel effectively certifies that it has the PLL5 clock speed and > AXP209 DCDC3 voltage fixes applied. > > It is still possible to set the CONFIG_OLD_SUNXI_KERNEL_COMPAT option > in U-Boot if the user desires to use an outdated unpatched sunxi-3.4 > kernel. > > Signed-off-by: Siarhei Siamashka <siarhei.siamas...@gmail.com>
Acked-by: Ian Campbell <i...@hellion.org.uk> _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
