From: Michael Turquette <mturquette@baylibre.com>
To: Julien Grall <julien.grall@arm.com>,
"Dirk Behme" <dirk.behme@de.bosch.com>,
linux-arm-kernel@lists.infradead.org,
"Mark Rutland" <mark.rutland@arm.com>,
devicetree@vger.kernel.org
Cc: xen-devel@lists.xenproject.org,
"Stefano Stabellini" <sstabellini@kernel.org>,
linux-clk@vger.kernel.org, "Stephen Boyd" <sboyd@codeaurora.org>
Subject: Re: [PATCH v2] xen/arm: register clocks used by the hypervisor
Date: Wed, 06 Jul 2016 13:42:28 -0700 [thread overview]
Message-ID: <146783774807.35356.6362595927321996311@resonance> (raw)
In-Reply-To: <577D035C.7090504@arm.com>
Hi Julien,
Quoting Julien Grall (2016-07-06 06:10:52)
> On 06/07/16 02:34, Michael Turquette wrote:
> > Hi!
> =
> Hello Michael,
> =
> > Quoting Dirk Behme (2016-06-30 03:32:32)
> >> 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.
> >
> > This whole thread had me confused until I realized that it all boiled
> > down to some nomenclature issues (for me).
> >
> > This code does not _register_ any clocks. It simply gets them and
> > enables them, which is what every other clk consumer in the Linux kernel
> > does. More details below.
> >
> >>
> >> 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
> >
> > clk_ignore_unused is a band-aid, not a proper medical solution. Setting
> > that flag will not turn clocks on for you, nor will it guarantee that
> > those clocks are never turned off in the future. It looks like you
> > figured this out correctly in the patch below but it is worth repeating.
> >
> > Also the new CLK_IS_CRITICAL flag might be of interest to you, but that
> > flag only exists as a way to enable clocks that must be enabled for the
> > system to function (hence, "critical") AND when those same clocks do not
> > have an accompanying Linux driver to consume them and enable them.
> =
> I don't think we want the kernel to enable the clock for the hypervisor. =
> We want to tell the kernel "don't touch at all to this clock, it does =
> not belong to you".
But the patch *does* touch the clock from the kernel. It enables the
clock via a call clk_prepare_enable. I'm utterly confused.
Regards,
Mike
> =
> Regards,
> =
> -- =
> Julien Grall
next prev parent reply other threads:[~2016-07-06 20:42 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-30 10:32 [PATCH v2] xen/arm: register clocks used by the hypervisor Dirk Behme
2016-06-30 14:21 ` Mark Rutland
2016-06-30 14:56 ` [Xen-devel] " Dirk Behme
2016-06-30 15:18 ` Mark Rutland
2016-06-30 15:33 ` Julien Grall
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 [this message]
2016-07-07 7:32 ` Dirk Behme
2016-07-08 2:50 ` Michael Turquette
2016-07-08 5:51 ` [Xen-devel] " Dirk Behme
2016-07-08 9:21 ` Julien Grall
2016-07-08 6:48 ` Dirk Behme
2016-07-08 9:35 ` Julien Grall
2016-07-05 6:50 Dirk Behme
2016-07-05 10:39 ` Mark Rutland
2016-07-05 10:45 ` Dirk Behme
2016-07-05 11:07 ` Mark Rutland
2016-07-06 23:38 ` Michael Turquette
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