linux-imx

/*

 *  Cyrix MediaGX and NatSemi Geode Suspend Modulation

 *  (C) 2002 Zwane Mwaikambo <zwane@commfireservices.com>

 *  (C) 2002 Hiroshi Miura   <miura@da-cha.org>

 *  All Rights Reserved

 *

 *  This program is free software; you can redistribute it and/or

 *      modify it under the terms of the GNU General Public License

 *      version 2 as published by the Free Software Foundation

 *

 *      The author(s) of this software shall not be held liable for damages

 *      of any nature resulting due to the use of this software. This

 *      software is provided AS-IS with no warranties.

 *

 * Theoretical note:

 *

 *  (see Geode(tm) CS5530 manual (rev.4.1) page.56)

 *

 *  CPU frequency control on NatSemi Geode GX1/GXLV processor and CS55x0

 *  are based on Suspend Modulation.

 *

 *  Suspend Modulation works by asserting and de-asserting the SUSP# pin

 *  to CPU(GX1/GXLV) for configurable durations. When asserting SUSP#

 *  the CPU enters an idle state. GX1 stops its core clock when SUSP# is

 *  asserted then power consumption is reduced.

 *

 *  Suspend Modulation's OFF/ON duration are configurable

 *  with 'Suspend Modulation OFF Count Register'

 *  and 'Suspend Modulation ON Count Register'.

 *  These registers are 8bit counters that represent the number of

 *  32us intervals which the SUSP# pin is asserted(ON)/de-asserted(OFF)

 *  to the processor.

 *

 *  These counters define a ratio which is the effective frequency

 *  of operation of the system.

 *

 *                 OFF Count

 *  F_eff = Fgx * ----------------------

 *                  OFF Count + ON Count

 *

 *  0 <= On Count, Off Count <= 255

 *

 *  From these limits, we can get register values

 *

 *  off_duration + on_duration <= MAX_DURATION

 *  on_duration = off_duration * (stock_freq - freq) / freq

 *

 *      off_duration  =  (freq * DURATION) / stock_freq

 *      on_duration = DURATION - off_duration

 *

 *

 *---------------------------------------------------------------------------

 *

 * ChangeLog:

 *  Dec. 12, 2003   Hiroshi Miura <miura@da-cha.org>

 *      - fix on/off register mistake

 *      - fix cpu_khz calc when it stops cpu modulation.

 *

 *  Dec. 11, 2002   Hiroshi Miura <miura@da-cha.org>

 *      - rewrite for Cyrix MediaGX Cx5510/5520 and

 *        NatSemi Geode Cs5530(A).

 *

 *  Jul. ??, 2002  Zwane Mwaikambo <zwane@commfireservices.com>