[v3,4/7] clk: qcom: hfpll: CLK_IGNORE_UNUSED

Commit Message

Niklas Cassel Nov. 25, 2019, 1:59 p.m. UTC

From: Jorge Ramirez-Ortiz <[e-mail]>

When COMMON_CLK_DISABLED_UNUSED is set, in an effort to save power and
to keep the software model of the clock in line with reality, the
framework transverses the clock tree and disables those clocks that
were enabled by the firmware but have not been enabled by any device
driver.

If CPUFREQ is enabled, early during the system boot, it might attempt
to change the CPU frequency ("set_rate"). If the HFPLL is selected as
a provider, it will then change the rate for this clock.

As boot continues, clk_disable_unused_subtree will run. Since it wont
find a valid counter (enable_count) for a clock that is actually
enabled it will attempt to disable it which will cause the CPU to
stop. Notice that in this driver, calls to check whether the clock is
enabled are routed via the is_enabled callback which queries the
hardware.

The following commit, rather than marking the clock critical and
forcing the clock to be always enabled, addresses the above scenario
making sure the clock is not disabled but it continues to rely on the
firmware to enable the clock.

Co-developed-by: Niklas Cassel <[e-mail]>
Signed-off-by: Niklas Cassel <[e-mail]>
Signed-off-by: Jorge Ramirez-Ortiz <[e-mail]>
Reviewed-by: Bjorn Andersson <[e-mail]>
---
Changes since v2:
-None

 drivers/clk/qcom/hfpll.c | 7 +++++++
 1 file changed, 7 insertions(+)

Comments

Stephen Boyd Dec. 19, 2019, 6:25 a.m. UTC | #1

Quoting Niklas Cassel (2019-11-25 05:59:06)
> From: Jorge Ramirez-Ortiz <[e-mail]>
> 
> When COMMON_CLK_DISABLED_UNUSED is set, in an effort to save power and
> to keep the software model of the clock in line with reality, the
> framework transverses the clock tree and disables those clocks that
> were enabled by the firmware but have not been enabled by any device
> driver.
> 
> If CPUFREQ is enabled, early during the system boot, it might attempt
> to change the CPU frequency ("set_rate"). If the HFPLL is selected as
> a provider, it will then change the rate for this clock.
> 
> As boot continues, clk_disable_unused_subtree will run. Since it wont
> find a valid counter (enable_count) for a clock that is actually
> enabled it will attempt to disable it which will cause the CPU to
> stop. Notice that in this driver, calls to check whether the clock is
> enabled are routed via the is_enabled callback which queries the
> hardware.
> 
> The following commit, rather than marking the clock critical and
> forcing the clock to be always enabled, addresses the above scenario
> making sure the clock is not disabled but it continues to rely on the
> firmware to enable the clock.
> 
> Co-developed-by: Niklas Cassel <[e-mail]>
> Signed-off-by: Niklas Cassel <[e-mail]>
> Signed-off-by: Jorge Ramirez-Ortiz <[e-mail]>
> Reviewed-by: Bjorn Andersson <[e-mail]>
> ---

Applied to clk-next

Patch

diff --git a/drivers/clk/qcom/hfpll.c b/drivers/clk/qcom/hfpll.c
index e64c0fd82fe4..225c675f6779 100644
--- a/drivers/clk/qcom/hfpll.c
+++ b/drivers/clk/qcom/hfpll.c
@@ -56,6 +56,13 @@  static int qcom_hfpll_probe(struct platform_device *pdev)
 		.parent_names = (const char *[]){ "xo" },
 		.num_parents = 1,
 		.ops = &clk_ops_hfpll,
+		/*
+		 * rather than marking the clock critical and forcing the clock
+		 * to be always enabled, we make sure that the clock is not
+		 * disabled: the firmware remains responsible of enabling this
+		 * clock (for more info check the commit log)
+		 */
+		.flags = CLK_IGNORE_UNUSED,
 	};
 	int ret;