• James Hogan's avatar
    clk: add support for clock reparent on set_rate · 71472c0c
    James Hogan authored
    Add core support to allow clock implementations to select the best
    parent clock when rounding a rate, e.g. the one which can provide the
    closest clock rate to that requested. This is by way of adding a new
    clock op, determine_rate(), which is like round_rate() but has an extra
    parameter to allow the clock implementation to optionally select a
    different parent clock. The core then takes care of reparenting the
    clock when setting the rate.
    The parent change takes place with the help of some new private data
    members. struct clk::new_parent specifies a clock's new parent (NULL
    indicates no change), and struct clk::new_child specifies a clock's new
    child (whose new_parent member points back to it). The purpose of these
    are to allow correct walking of the future tree for notifications prior
    to actually reparenting any clocks, specifically to skip child clocks
    who are being reparented to another clock (they will be notified via the
    new parent), and to include any new child clock. These pointers are set
    by clk_calc_subtree(), and the new_child pointer gets cleared when a
    child is actually reparented to avoid duplicate POST_RATE_CHANGE
    Each place where round_rate() is called, determine_rate() is checked
    first and called in preference. This restructures a few of the call
    sites to simplify the logic into if/else blocks.
    Signed-off-by: default avatarJames Hogan <james.hogan@imgtec.com>
    Reviewed-by: default avatarStephen Boyd <sboyd@codeaurora.org>
    Cc: Mike Turquette <mturquette@linaro.org>
    Cc: linux-arm-kernel@lists.infradead.org
    Signed-off-by: default avatarMike Turquette <mturquette@linaro.org>
clk.txt 9.25 KB