On 01/12/2015 06:49 PM, Dr. H. Nikolaus Schaller wrote:
Hi,
Am 12.01.2015 um 13:13 schrieb Grazvydas Ignotas notasas@gmail.com:
On Sun, Jan 11, 2015 at 2:18 PM, Dr. H. Nikolaus Schaller hns@goldelico.com wrote:
On the other side I think Notaz wants to do optimizations that never will be accepted by linus/master. So this still needs a separate tree.
Yeah, we'll want overclocking at least, which is forbidden in mainline. We'll also want hardware virtualization support, which needs PAE enabled in kernel, and PAE kernels can only run on Cortex-A15 or newer, which means one-uImage-for-everyone is not possible here.
Ok, but if I understand the recent development directions correctly, both might be reduced to a modified (overlaid) device tree and a modified kernel config and I would hope that in the future PAE is ignored by pre-A15 CPUs (if not defined by DT).
But I am not a specialist of either topic (I even thought that PAE is only for x86 but learned about CONFIG_ARM_LPAE).
Right, it's LPAE on ARM. With this setting ARM CPU is switched to different mode that uses page tables in completely different format from classic ARM. Linux memory management subsystem is deeply tied into page table format, and different page table format support is implemented using multiple levels of macros, so there is currently no way to support both with single binary. Theoretically it may possible to implement multiple format support in single binary, but I don't think it will ever happen in practice (it hasn't happened for IA32 either and distributions offer separate kernels with PAE on and off).
Grazvydas