Re: [Xen-devel] [PATCH] xen/arm: register clocks used by the hypervisor

[Dirk Behme <dirk.behme@xxxxxxxxxxxx>]

On 21.06.2016 12:16, Dirk Behme wrote:
> Some clocks might be used by the Xen hypervisor and not by the Linux
> kernel. If these are not registered by the Linux kernel, they might be
> disabled by clk_disable_unused() as the kernel doesn't know that they
> are used. The clock of the serial console handled by Xen is one
> example for this. It might be disabled by clk_disable_unused() which
> stops the whole serial output, even from Xen, then.
>
> Up to now, the workaround for this has been to use the Linux kernel
> command line parameter 'clk_ignore_unused'. See Xen bug
>
> http://bugs.xenproject.org/xen/bug/45
>
> too.
>
> To fix this, we will add the "unused" clocks in Xen to the hypervisor
> node. The Linux kernel has to register the clocks from the hypervisor
> node, then.
>
> Therefore, check if there is a "clocks" entry in the hypervisor node
> and if so register the given clocks to the Linux kernel clock
> framework and with this mark them as used. This prevents the clocks
> from being disabled.

Just for the logs, the Xen counterpart is

https://lists.xen.org/archives/html/xen-devel/2016-06/msg02607.html

Dirk


> ---
>  arch/arm/xen/enlighten.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 75cd734..ee6e81f 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -22,6 +22,7 @@
>  #include <linux/of.h>
>  #include <linux/of_irq.h>
>  #include <linux/of_address.h>
> +#include <linux/clk-provider.h>
>  #include <linux/cpuidle.h>
>  #include <linux/cpufreq.h>
>  #include <linux/cpu.h>
> @@ -381,6 +382,40 @@ static int __init xen_pm_init(void)
>  }
>  late_initcall(xen_pm_init);
>
> +/*
> + * Check if we want to register some clocks, that they
> + * are not freed because unused by clk_disable_unused().
> + * E.g. the serial console clock.
> + */
> +static int __init xen_arm_register_clks(void)
> +{
> +       struct clk *clk;
> +       unsigned int i, count;
> +       int ret;
> +
> +       count = of_clk_get_parent_count(xen_node);
> +       if (!count)
> +               return 0;
> +
> +       for (i = 0; i < count; i++) {
> +               clk = of_clk_get(xen_node, i);
> +               if (IS_ERR(clk)) {
> +                       pr_err("Xen failed to register clock %i. Error: %li\n",
> +                              i, PTR_ERR(clk));
> +                       return PTR_ERR(clk);
> +               }
> +
> +               ret = clk_prepare_enable(clk);
> +               if (ret < 0) {
> +                       pr_err("Xen failed to enable clock %i. Error: %i\n",
> +                              i, ret);
> +                       return ret;
> +               }
> +       }
> +
> +       return 0;
> +}
> +late_initcall(xen_arm_register_clks);
>
>  /* empty stubs */
>  void xen_arch_pre_suspend(void) { }



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