• Heiko Stübner's avatar
    [CPUFREQ] Add S3C2416/S3C2450 cpufreq driver · 34ee5507
    Heiko Stübner authored
    The S3C2416/S3C2450 SoCs support two sources for the armclk.
    
    The first source is the so called armdiv which divides the msysclk down
    to provide necessary cpu rates. In this mode the core voltage must be
    always at 1.3V. The frequency from the armdiv is not allowed to be
    lower than the hclk frequency.
    
    In the second mode the armclk can be sourced directly from the hclk in
    the so called "dynamic voltags scaling" (dvs) mode. Here the armdiv
    isn't used at all. Also in this mode the core voltage may be lowered.
    Existing hardware and tests with it suggest 1.0V as sufficient.
    
    When changing the clock source to the armdiv from the hclk, the SoC
    shows stability issues if the new frequency is higher than the current
    hclk frequency. Hence the driver always forces the armdiv to the hclk
    frequency before the source change and lets the cpufreq issue another
    set_target call for higher frequencies.
    
    To mark the hclk frequency as lower as the corresponding armdiv
    frequency it is set 1MHz below the real frequency. This lets the cpufreq
    framework change between 133MHz based on hclk and 133MHz based on armdiv
    at will.
    Signed-off-by: default avatarHeiko Stuebner <heiko@sntech.de>
    Tested-by: default avatarAndrey Gusakov <dron0gus@gmail.com>
    Signed-off-by: default avatarDave Jones <davej@redhat.com>
    34ee5507
Makefile 2.27 KB