On 13/04/17 07:27, Peng Fan wrote:
Hi,
-----Original Message----- From: Stefano Babic [mailto:sbabic@denx.de] Sent: Thursday, April 13, 2017 2:24 PM To: Peng Fan peng.fan@nxp.com; Stefano Babic sbabic@denx.de Cc: van.freenix@gmail.com; u-boot@lists.denx.de; andre.przywara@arm.com; Albert ARIBAUD albert.u.boot@aribaud.net Subject: Re: [PATCH 1/2] imx-common: Enable ACTLR.SMP bit for i.MX cortex- a7 platforms
Hi Peng,
On 13/04/2017 05:05, Peng Fan wrote:
Anyway, it looks to me wrong to fix this in i.MX code, as this must be fixed for all Cortex-A7. It should be fixed in general ARM code.
And Andre has already sent patches for this (at least for sunxi), but with the opposite rule (default is set if not specific requested).
Thanks for correcting me. I see Andre's patch https://lists.denx.de/pipermail/u-boot/2017-February/279918.html
It only handles sunxi platform. If we need fix i.MX A7 cores, do you prefer I
set the SMP bit in s_init for i.MX6UL/7?
Or you prefer this should be handled by common ARM code?
As far as I understand, this issue is common to all A7 cores ==> fix should be in common ARM code.
Well, it's not only common to all A7 cores, actually all ARMv7 SMP Cortex cores (A5, A7, A9, A15, A17) need this. Cortex-A8 is UP only, so does not have this bit. Sometimes this bit is set by other boot code before U-Boot (hence not every board might need this). ARMv8 Cortex cores have this bit as well, just in the CPUECTLR register. So looking at arm64, I find (in arch/arm/cpu/armv8/Kconfig): ============ config ARMV8_SET_SMPEN bool "Enable data coherency with other cores in cluster" help Say Y here if there is not any trust firmware to set CPUECTLR_EL1.SMPEN bit before U-Boot. .... ============
So I'd suggest to piggy back on this, either by moving this Kconfig option to some shared ARM code path, or by replicating this option to some ARMv7 Kconfig file.
Ok. Since there is no Cortex-A[x] revision check in U-Boot, need to first add the code.
Mmh, do you mean auto-detection during runtime? As in: if (MIDR == CortexA7) set_smp_bit();
The problem with this is that U-Boot might not be able to access the register (access to ACTLR from non-secure world can be forbidden by secure world).
So I'd go with a Kconfig option. Boards or platforms that need it could just select it. We just need to find a nice place to put the code, maybe in arch/arm/cpu/armv7/start.S. And another problem is that is needs to be set on every core in the system (like arch/arm/cpu/armv7/psci.S does already in psci_enable_smp). So it cannot really work for systems without PSCI or those not bringing all cores into U-Boot.
Cheers, Andre.
Then set ACTLR.SMP for A7 SMP.
Regards, Peng.