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Re: [Xen-devel] [PATCH v4] xen/arm: Add a clock property
- To: Julien Grall <julien.grall@xxxxxxx>, Michael Turquette <mturquette@xxxxxxxxxxxx>, Dirk Behme <dirk.behme@xxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
- Date: Thu, 14 Jul 2016 12:32:57 +0200
- Cc: Mark Rutland <mark.rutland@xxxxxxx>, devicetree@xxxxxxxxxxxxxxx, Stephen Boyd <sboyd@xxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-clk@xxxxxxxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 14 Jul 2016 10:33:08 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 14.07.2016 12:14, Julien Grall wrote:
Hi Dirk,
On 14/07/16 07:31, Dirk Behme wrote:
On 13.07.2016 23:03, Michael Turquette wrote:
Quoting Dirk Behme (2016-07-13 11:56:30)
On 13.07.2016 20:43, Stefano Stabellini wrote:
On Wed, 13 Jul 2016, Dirk Behme wrote:
On 13.07.2016 00:26, Michael Turquette wrote:
Quoting Dirk Behme (2016-07-12 00:46:45)
Clocks described by this property are reserved for use by Xen,
and the OS
must not alter their state any way, such as disabling or gating a
clock,
or modifying its rate. Ensuring this may impose constraints on
parent
clocks or other resources used by the clock tree.
Note that clk_prepare_enable will not prevent the rate from changing
(clk_set_rate) or a parent from changing (clk_set_parent). The
only way
to do this currently would be to set the following flags on the
effected
clocks:
CLK_SET_RATE_GATE
CLK_SET_PARENT_GATE
Regarding setting flags, I think we already talked about that. I
think the
conclusion was that in our case its not possible to manipulate the
flags in
the OS as this isn't intended to be done in cases like ours.
Therefore no API
is exported for this.
I.e. if we need to set these flags, we have to do that in Xen where
we add the
clocks to the hypervisor node in the device tree. And not in the
kernel patch
discussed here.
These are internal Linux flags, aren't they?
I've been under the impression that you can set clock "flags" via the
device tree. Seems I need to re-check that ;)
Right, you cannot set flags from the device tree. Also, setting these
flags is done by the clock provider driver, not a consumer. Xen is the
consumer.
Ok, thanks, then I think we can forget about using flags for the issue
we are discussing here.
Best regards
Dirk
P.S.: Would it be an option to merge the v4 patch we are discussing
here, then? From the discussion until here, it sounds to me that it's
the best option we have at the moment. Maybe improving it in the future,
then.
I think it is a good start, although I would like to see some rationale
in the code and commit message about the behavior of the Linux with
those clocks after this patch because it does not match the "contract".
I'd be happy about any wording proposals :)
Best regards
Dirk
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