From: Mark Rutland <mark.rutland@arm.com>
To: Dirk Behme <dirk.behme@de.bosch.com>
Cc: linux-arm-kernel@lists.infradead.org,
Julien Grall <julien.grall@arm.com>,
devicetree@vger.kernel.org, xen-devel@lists.xenproject.org,
Stefano Stabellini <sstabellini@kernel.org>,
linux-clk@vger.kernel.org,
Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@codeaurora.org>
Subject: Re: [PATCH v2] xen/arm: register clocks used by the hypervisor
Date: Tue, 5 Jul 2016 11:39:17 +0100 [thread overview]
Message-ID: <20160705103917.GC20478@leverpostej> (raw)
In-Reply-To: <1467701423-31138-1-git-send-email-dirk.behme@de.bosch.com>
Hi,
On Tue, Jul 05, 2016 at 08:50:23AM +0200, 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.
>
> Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
> ---
> Changes in v2: Drop the Linux implementation details like clk_disable_unused
> in xen.txt.
Thanks for doing this.
> Documentation/devicetree/bindings/arm/xen.txt | 13 ++++++++
> arch/arm/xen/enlighten.c | 47 +++++++++++++++++++++++++++
> 2 files changed, 60 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/arm/xen.txt b/Documentation/devicetree/bindings/arm/xen.txt
> index c9b9321..21fd469 100644
> --- a/Documentation/devicetree/bindings/arm/xen.txt
> +++ b/Documentation/devicetree/bindings/arm/xen.txt
> @@ -17,6 +17,19 @@ the following properties:
> A GIC node is also required.
> This property is unnecessary when booting Dom0 using ACPI.
>
> +Optional properties:
> +
> +- clocks: one or more clocks to be registered.
> + Xen hypervisor drivers might replace native drivers, resulting in
> + clocks not registered by these native drivers. To avoid that these
> + unregistered clocks are disabled by the Linux kernel initialization
> + register them in the hypervisor node.
> + An example for this are the clocks of a serial driver already enabled
> + by the firmware. If the clocks used by the serial hardware interface
> + are not registered by the serial driver itself the serial output
> + might stop once the Linux kernel initialization disables the 'unused'
> + clocks.
The above describes the set of problems, but doesn't set out the actual
contract. It also covers a number of Linux implementation details in
abstract.
As I commented previously [1], the binding should describe the set of
guarantees that you rewquire (e.g. that the clocks must be left as-is,
not gated, and their rates left unchanged).
Please describe the specific set of guarantees that you require.
Thanks,
Mark.
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/440434.html
next prev parent reply other threads:[~2016-07-05 10:39 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-05 6:50 [PATCH v2] xen/arm: register clocks used by the hypervisor Dirk Behme
2016-07-05 10:39 ` Mark Rutland [this message]
2016-07-05 10:45 ` Dirk Behme
2016-07-05 11:07 ` Mark Rutland
2016-07-06 23:38 ` Michael Turquette
-- strict thread matches above, loose matches on Subject: below --
2016-06-30 10:32 Dirk Behme
2016-06-30 14:21 ` Mark Rutland
2016-07-05 13:53 ` Stefano Stabellini
2016-07-05 13:54 ` Julien Grall
2016-07-05 14:02 ` Julien Grall
2016-07-05 14:04 ` Stefano Stabellini
2016-07-05 14:08 ` Julien Grall
2016-07-05 14:37 ` Stefano Stabellini
2016-07-06 1:34 ` Michael Turquette
2016-07-06 13:10 ` Julien Grall
2016-07-06 13:16 ` Stefano Stabellini
2016-07-06 13:26 ` Julien Grall
2016-07-06 13:48 ` Mark Rutland
2016-07-06 20:42 ` Michael Turquette
2016-07-07 7:32 ` Dirk Behme
2016-07-08 2:50 ` Michael Turquette
2016-07-08 6:48 ` Dirk Behme
2016-07-08 9:35 ` Julien Grall
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