mirror of https://github.com/hak5/openwrt.git
130 lines
4.4 KiB
Diff
130 lines
4.4 KiB
Diff
Content-Type: text/plain; charset="utf-8"
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MIME-Version: 1.0
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Content-Transfer-Encoding: 7bit
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Subject: [v3, 03/13] clk: Avoid sending high rates to downstream clocks during
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set_rate
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From: Stephen Boyd <sboyd@codeaurora.org>
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X-Patchwork-Id: 6063271
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Message-Id: <1426920332-9340-4-git-send-email-sboyd@codeaurora.org>
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To: Mike Turquette <mturquette@linaro.org>, Stephen Boyd <sboyd@codeaurora.org>
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Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
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linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
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Viresh Kumar <viresh.kumar@linaro.org>
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Date: Fri, 20 Mar 2015 23:45:22 -0700
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If a clock is on and we call clk_set_rate() on it we may get into
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a situation where the clock temporarily increases in rate
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dramatically while we walk the tree and call .set_rate() ops. For
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example, consider a case where a PLL feeds into a divider.
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Initially the divider is set to divide by 1 and the PLL is
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running fairly slow (100MHz). The downstream consumer of the
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divider output can only handle rates =< 400 MHz, but the divider
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can only choose between divisors of 1 and 4.
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+-----+ +----------------+
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| PLL |-->| div 1 or div 4 |---> consumer device
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+-----+ +----------------+
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To achieve a rate of 400MHz on the output of the divider, we
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would have to set the rate of the PLL to 1.6 GHz and then divide
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it by 4. The current code would set the PLL to 1.6GHz first while
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the divider is still set to 1, thus causing the downstream
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consumer of the clock to receive a few clock cycles of 1.6GHz
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clock (far beyond it's maximum acceptable rate). We should be
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changing the divider first before increasing the PLL rate to
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avoid this problem.
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Therefore, set the rate of any child clocks that are increasing
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in rate from their current rate so that they can increase their
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dividers if necessary. We assume that there isn't such a thing as
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minimum rate requirements.
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Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
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---
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drivers/clk/clk.c | 34 ++++++++++++++++++++++------------
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1 file changed, 22 insertions(+), 12 deletions(-)
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--- a/drivers/clk/clk.c
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+++ b/drivers/clk/clk.c
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@@ -1476,21 +1476,23 @@ static struct clk *clk_propagate_rate_ch
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* walk down a subtree and set the new rates notifying the rate
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* change on the way
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*/
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-static void clk_change_rate(struct clk *clk)
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+static void clk_change_rate(struct clk *clk, unsigned long best_parent_rate)
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{
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struct clk *child;
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struct hlist_node *tmp;
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unsigned long old_rate;
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- unsigned long best_parent_rate = 0;
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bool skip_set_rate = false;
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struct clk *old_parent;
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- old_rate = clk->rate;
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+ hlist_for_each_entry(child, &clk->children, child_node) {
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+ /* Skip children who will be reparented to another clock */
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+ if (child->new_parent && child->new_parent != clk)
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+ continue;
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+ if (child->new_rate > child->rate)
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+ clk_change_rate(child, clk->new_rate);
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+ }
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- if (clk->new_parent)
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- best_parent_rate = clk->new_parent->rate;
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- else if (clk->parent)
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- best_parent_rate = clk->parent->rate;
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+ old_rate = clk->rate;
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if (clk->new_parent && clk->new_parent != clk->parent) {
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old_parent = __clk_set_parent_before(clk, clk->new_parent);
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@@ -1510,7 +1512,7 @@ static void clk_change_rate(struct clk *
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if (!skip_set_rate && clk->ops->set_rate)
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clk->ops->set_rate(clk->hw, clk->new_rate, best_parent_rate);
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- clk->rate = clk_recalc(clk, best_parent_rate);
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+ clk->rate = clk->new_rate;
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if (clk->notifier_count && old_rate != clk->rate)
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__clk_notify(clk, POST_RATE_CHANGE, old_rate, clk->rate);
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@@ -1523,12 +1525,13 @@ static void clk_change_rate(struct clk *
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/* Skip children who will be reparented to another clock */
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if (child->new_parent && child->new_parent != clk)
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continue;
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- clk_change_rate(child);
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+ if (child->new_rate != child->rate)
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+ clk_change_rate(child, clk->new_rate);
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}
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/* handle the new child who might not be in clk->children yet */
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- if (clk->new_child)
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- clk_change_rate(clk->new_child);
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+ if (clk->new_child && clk->new_child->new_rate != clk->new_child->rate)
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+ clk_change_rate(clk->new_child, clk->new_rate);
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}
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/**
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@@ -1556,6 +1559,7 @@ int clk_set_rate(struct clk *clk, unsign
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{
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struct clk *top, *fail_clk;
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int ret = 0;
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+ unsigned long parent_rate;
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if (!clk)
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return 0;
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@@ -1589,8 +1593,13 @@ int clk_set_rate(struct clk *clk, unsign
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goto out;
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}
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+ if (top->parent)
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+ parent_rate = top->parent->rate;
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+ else
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+ parent_rate = 0;
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+
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/* change the rates */
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- clk_change_rate(top);
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+ clk_change_rate(top, parent_rate);
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out:
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clk_prepare_unlock();
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