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If the user wants to build the sunxi version of the kernel they can specify the PREFERRED_PROVIDER block in their conf/local.conf (i.e. they don't need to edit the layer explicitly). Also, now that gcc-5.2 is the default on master, inform the user how they can continue to build the sunxi version (3.4%) version of the kernel by forcing the compiler to version 4.9. Signed-off-by: Trevor Woerner <twoerner@gmail.com>
72 lines
2.8 KiB
Markdown
72 lines
2.8 KiB
Markdown
meta-sunxi
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==============
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Official sunxi OpenEmbedded layer for Allwinner-based boards.
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This layer depends on the additional layer:
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meta-openembedded: git://git.openembedded.org/meta-openembedded
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Tested with core-image-base.
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Maintainers:
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* Nicolas Aguirre <aguirre.nicolas@gmail.com>
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* Enrico Butera <ebutera@users.sourceforge.net>
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* Sergey Lapin <slapin@ossfans.org>
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Kernel / U-Boot Version
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===========
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Most Allwinner devices and hardware are supported in mainline kernel and U-Boot, so this layer builds mainline by default.
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There is a custom U-Boot and Kernel version for sunxi devices which includes some special drivers not mainlined.
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These versions are rather old (3.4 for kernel and 2014.04 for U-Boot), but may support more functions and devices than current mainline
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If you want to switch back to sunxi versions for some reasons (no device tree available, unsupported hardware), either:
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- change the file conf/machine/include/sunxi.inc to include the following block
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- edit your conf/local.conf to add the following block
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PREFERRED_PROVIDER_u-boot="u-boot-sunxi"
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PREFERRED_PROVIDER_virtual/bootloader="u-boot-sunxi"
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PREFERRED_PROVIDER_virtual/kernel="linux-sunxi"
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If you already have built the mainline versions it might be necessary to reset the build directories with:
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bitbake -c clean linux
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bitbake -c clean u-boot
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Also, older kernel versions such as this don't build successfully with any gcc version 5.0 or newer. Since gcc-5.2 is the current
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default compiler on master, if you wish to build this kernel with master you'll need to add the following to your conf/local.conf:
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GCCVERSION = "4.9%"
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Performance
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===========
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The default machine settings are meant to be the lowest common denominator, maximizing generality.
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Significantly better performance (2x-3x) can be achieved with the following settings:
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**_Allwinner A20_**
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For Allwinner A20 (Cubieboard2/CubieTruck), the following tuning options are recommended:
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_Enable hardfloat, thumb2 and neon capabilities_
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DEFAULTTUNE = "cortexa7hf-neon-vfpv4"
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This tuning profile takes advantage of the Allwinner A20 hardfloat, neon and vfpv4 capabilities.
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_Change CPU governor to ondemand, and tune settings_
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echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
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echo 336000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
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echo 912000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
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#More aggressive
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#echo 1008000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
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echo 40 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
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echo 200000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate
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This code changes the default CPU governor from _fantasy_ to _ondemand_, and tunes its settings, as recommended at http://linux-sunxi.org/Cpufreq
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For additional discussion, see https://github.com/linux-sunxi/meta-sunxi/issues/25
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