• Christian Sünkenberg's avatar
    x86/cpu/cyrix: Add alternative Device ID of Geode GX1 SoC · ae1d557d
    Christian Sünkenberg authored
    A SoC variant of Geode GX1, notably NSC branded SC1100, seems to
    report an inverted Device ID in its DIR0 configuration register,
    specifically 0xb instead of the expected 0x4.
    
    Catch this presumably quirky version so it's properly recognized
    as GX1 and has its cache switched to write-back mode, which provides
    a significant performance boost in most workloads.
    
    SC1100's datasheet "Geode SC1100 Information Appliance On a Chip",
    states in section 1.1.7.1 "Device ID" that device identification
    values are specified in SC1100's device errata. These, however,
    seem to not have been publicly released.
    
    Wading through a number of boot logs and /proc/cpuinfo dumps found on
    pastebin and blogs, this patch should mostly be relevant for a number
    of now admittedly aging Soekris NET4801 and PC Engines WRAP devices,
    the latter being the platform this issue was discovered on.
    Performance impact was verified using "openssl speed", with
    write-back caching scaling throughput between -3% and +41%.
    Signed-off-by: default avatarChristian Sünkenberg <christian.suenkenberg@student.kit.edu>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/1496596719.26725.14.camel@student.kit.eduSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    ae1d557d
cyrix.c 12.1 KB