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   4 Subject: [v3, 03/13] clk: Avoid sending high rates to downstream clocks during
   5         set_rate
   6 From: Stephen Boyd <sboyd@codeaurora.org>
   7 X-Patchwork-Id: 6063271
   8 Message-Id: <1426920332-9340-4-git-send-email-sboyd@codeaurora.org>
   9 To: Mike Turquette <mturquette@linaro.org>, Stephen Boyd <sboyd@codeaurora.org>
  10 Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
  11         linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
  12         Viresh Kumar <viresh.kumar@linaro.org>
  13 Date: Fri, 20 Mar 2015 23:45:22 -0700
  14
  15 If a clock is on and we call clk_set_rate() on it we may get into
  16 a situation where the clock temporarily increases in rate
  17 dramatically while we walk the tree and call .set_rate() ops. For
  18 example, consider a case where a PLL feeds into a divider.
  19 Initially the divider is set to divide by 1 and the PLL is
  20 running fairly slow (100MHz). The downstream consumer of the
  21 divider output can only handle rates =< 400 MHz, but the divider
  22 can only choose between divisors of 1 and 4.
  23
  24  +-----+   +----------------+
  25  | PLL |-->| div 1 or div 4 |---> consumer device
  26  +-----+   +----------------+
  27
  28 To achieve a rate of 400MHz on the output of the divider, we
  29 would have to set the rate of the PLL to 1.6 GHz and then divide
  30 it by 4. The current code would set the PLL to 1.6GHz first while
  31 the divider is still set to 1, thus causing the downstream
  32 consumer of the clock to receive a few clock cycles of 1.6GHz
  33 clock (far beyond it's maximum acceptable rate). We should be
  34 changing the divider first before increasing the PLL rate to
  35 avoid this problem.
  36
  37 Therefore, set the rate of any child clocks that are increasing
  38 in rate from their current rate so that they can increase their
  39 dividers if necessary. We assume that there isn't such a thing as
  40 minimum rate requirements.
  41
  42 Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
  43
  44 ---
  45 drivers/clk/clk.c | 34 ++++++++++++++++++++++------------
  46  1 file changed, 22 insertions(+), 12 deletions(-)
  47
  48 --- a/drivers/clk/clk.c
  49 +++ b/drivers/clk/clk.c
  50 @@ -1476,21 +1476,23 @@ static struct clk *clk_propagate_rate_ch
  51   * walk down a subtree and set the new rates notifying the rate
  52   * change on the way
  53   */
  54 -static void clk_change_rate(struct clk *clk)
  55 +static void clk_change_rate(struct clk *clk, unsigned long best_parent_rate)
  56  {
  57         struct clk *child;
  58         struct hlist_node *tmp;
  59         unsigned long old_rate;
  60 -       unsigned long best_parent_rate = 0;
  61         bool skip_set_rate = false;
  62         struct clk *old_parent;
  63
  64 -       old_rate = clk->rate;
  65 +       hlist_for_each_entry(child, &clk->children, child_node) {
  66 +               /* Skip children who will be reparented to another clock */
  67 +               if (child->new_parent && child->new_parent != clk)
  68 +                       continue;
  69 +               if (child->new_rate > child->rate)
  70 +                       clk_change_rate(child, clk->new_rate);
  71 +       }
  72
  73 -       if (clk->new_parent)
  74 -               best_parent_rate = clk->new_parent->rate;
  75 -       else if (clk->parent)
  76 -               best_parent_rate = clk->parent->rate;
  77 +       old_rate = clk->rate;
  78
  79         if (clk->new_parent && clk->new_parent != clk->parent) {
  80                 old_parent = __clk_set_parent_before(clk, clk->new_parent);
  81 @@ -1510,7 +1512,7 @@ static void clk_change_rate(struct clk *
  82         if (!skip_set_rate && clk->ops->set_rate)
  83                 clk->ops->set_rate(clk->hw, clk->new_rate, best_parent_rate);
  84
  85 -       clk->rate = clk_recalc(clk, best_parent_rate);
  86 +       clk->rate = clk->new_rate;
  87
  88         if (clk->notifier_count && old_rate != clk->rate)
  89                 __clk_notify(clk, POST_RATE_CHANGE, old_rate, clk->rate);
  90 @@ -1523,12 +1525,13 @@ static void clk_change_rate(struct clk *
  91                 /* Skip children who will be reparented to another clock */
  92                 if (child->new_parent && child->new_parent != clk)
  93                         continue;
  94 -               clk_change_rate(child);
  95 +               if (child->new_rate != child->rate)
  96 +                       clk_change_rate(child, clk->new_rate);
  97         }
  98
  99         /* handle the new child who might not be in clk->children yet */
 100 -       if (clk->new_child)
 101 -               clk_change_rate(clk->new_child);
 102 +       if (clk->new_child && clk->new_child->new_rate != clk->new_child->rate)
 103 +               clk_change_rate(clk->new_child, clk->new_rate);
 104  }
 105
 106  /**
 107 @@ -1556,6 +1559,7 @@ int clk_set_rate(struct clk *clk, unsign
 108  {
 109         struct clk *top, *fail_clk;
 110         int ret = 0;
 111 +       unsigned long parent_rate;
 112
 113         if (!clk)
 114                 return 0;
 115 @@ -1589,8 +1593,13 @@ int clk_set_rate(struct clk *clk, unsign
 116                 goto out;
 117         }
 118
 119 +       if (top->parent)
 120 +               parent_rate = top->parent->rate;
 121 +       else
 122 +               parent_rate = 0;
 123 +
 124         /* change the rates */
 125 -       clk_change_rate(top);
 126 +       clk_change_rate(top, parent_rate);
 127
 128  out:
 129         clk_prepare_unlock();