View source for 12297

OLPC has enabled the second processor core in the XO-4 laptops.

== Problem ==

The released operating systems [[13.2.1]] and [[13.2.2]] run only one core.  The XO-4 underperforms compared to some other devices.

== Solution ==

XO-4 only:

Upgrade to [[13.2.6]].

== Workaround ==

Care is needed.  Without the firmware upgrade, our dual-core kernel will not boot.  With the firmware upgrade, the original kernel will not boot. The reason for the restriction is that changes to firmware and kernel must occur at the same time. 

On unsecure laptops running [[13.2.0]], [[13.2.1]] and [[13.2.2]], upgrade the kernel and the firmware at the same time.  The exact steps are:

* download the [http://rpmdropbox.laptop.org/f18-xo4/kernel-3.5.7_xo4-20150610.0359.olpc.97336f6.armv7hl.rpm kernel-3.5.7_xo4-20150610.0359.olpc.97336f6.armv7hl.rpm] kernel package,
* download the [http://dev.laptop.org/pub/firmware/q7c05/q7c05.rom q7c05.rom] new firmware,
* copy both to a USB drive,
* add battery and power cable, and wait for the laptop to finish charging,
* upgrade the kernel,
 sudo rpm -U kernel-3.5.7_xo4-20150610.0359.olpc.97336f6.armv7hl.rpm
* shutdown,
 sudo poweroff
* upgrade the firmware,
 ok flash u:\q7c05.rom
* allow the laptop to boot, and verify dual-core operation:
 bash-4.2# cat /proc/cpuinfo
 Processor       : ARMv7 Processor rev 2 (v7l)
 processor       : 0
 BogoMIPS        : 1196.85
 
 processor       : 1
 BogoMIPS        : 1196.85
 
 Features        : swp half thumb fastmult vfp edsp iwmmxt thumbee neon vfpv3 tls 
 CPU implementer : 0x56
 CPU architecture: 7
 CPU variant     : 0x2
 CPU part        : 0x584
 CPU revision    : 2
 
 Hardware        : Marvell MMP3 (Device Tree Support) OLPC XO-4
 Revision        : 0000
 Serial          : 0000000000000000
 -bash-4.2# █

To add dual core to a build of Fedora 18, add the kernel and firmware packages to your build.

== Reverting ==

* download the [http://rpmdropbox.laptop.org/f18-xo4/kernel-3.5.7_xo4-20141118.2329.olpc.cd558cf.armv7hl.rpm 3.5.7_xo4-20141118.2329.olpc.cd558cf] kernel package,
* download the [http://dev.laptop.org/pub/firmware/q7b45/q7b45.rom q7b45.rom] old firmware,
* copy both to a USB drive,
* downgrade the kernel,
* shutdown,
 sudo poweroff
* downgrade the firmware,
 ok flash u:\q7b45.rom
* allow the laptop to boot.

== Using a single core kernel on 14.1.0 ==

Certain tasks may benefit from the higher memory allocation bandwidth of the single core kernel.

* download the [http://rpmdropbox.laptop.org/f18-xo4/kernel-3.5.7_xo4-20141118.2329.olpc.cd558cf.armv7hl.rpm 3.5.7_xo4-20141118.2329.olpc.cd558cf] kernel package,
* download the [http://dev.laptop.org/pub/firmware/q7b45/q7b45.rom q7b45.rom] old firmware,
* copy both to a USB drive,
* <font color="red">note</font>: remove the /bootpart/boot/bootfw4.zip file, to prevent automatic firmware upgrade;
 sudo rm /bootpart/boot/bootfw4.zip
* downgrade the kernel, by forcing upgrade to lower version;
 sudo rpm --upgrade --force \
 kernel-3.5.7_xo4-20141118.2329.olpc.cd558cf.armv7hl.rpm
* shutdown,
 sudo poweroff
* downgrade the firmware,
 ok flash u:\q7b45.rom
* allow the laptop to boot, and verify single-core operation:
 -bash-4.2# cat /proc/cpuinfo 
 Processor       : ARMv7 Processor rev 2 (v7l)
 BogoMIPS        : 1191.11
 Features        : swp half thumb fastmult vfp edsp iwmmxt thumbee neon vfpv3 tls 
 CPU implementer : 0x56
 CPU architecture: 7
 CPU variant     : 0x2
 CPU part        : 0x584
 CPU revision    : 2
 
 Hardware        : Marvell MMP2 (Device Tree Support)
 Revision        : 0000
 Serial          : 0000000000000000
 -bash-4.2# █

== Booting a single core kernel on dual core firmware ==

For manual use only.  Disable the dual core feature before booting, like this:

 ok patch noop mmp3-gic linux-fixup
 ok boot█

Do not deploy this workaround, as it causes a power draw regression.

== See Also ==
* [http://dev.laptop.org/ticket/12297 ticket #12297],