linux-kernel - Re: [PATCH v2] clk: Introduce clk_has

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Date:	Fri, 23 Jan 2015 10:34:10 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Mike Turquette <mturquette@...aro.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Subject: Re: [PATCH v2] clk: Introduce clk_has_parent()

On Thu, Jan 22, 2015 at 12:25:46PM -0800, Stephen Boyd wrote:
> On 01/22, Thierry Reding wrote:
> > On Wed, Jan 21, 2015 at 04:16:05PM -0800, Stephen Boyd wrote:
> > > On 01/21/2015 08:13 AM, Thierry Reding wrote:
> > > > From: Thierry Reding <treding@...dia.com>
> > > >
> > > > This new function is similar to clk_set_parent(), except that it doesn't
> > > > actually change the parent. It merely checks that the given parent clock
> > > > can be a parent for the given clock.
> > > >
> > > > A situation where this is useful is to check that a particular setup is
> > > > valid before switching to it. One specific use-case for this is atomic
> > > > modesetting in the DRM framework where setting a mode is divided into a
> > > > check phase where a given configuration is validated before applying
> > > > changes to the hardware.
> > > >
> > > > Cc: Russell King <linux@....linux.org.uk>
> > > > Cc: Mike Turquette <mturquette@...aro.org>
> > > > Cc: Stephen Boyd <sboyd@...eaurora.org>
> > > > Signed-off-by: Thierry Reding <treding@...dia.com>
> > > > ---
> > > 
> > > Reviewed-by: Stephen Boyd <sboyd@...eaurora.org>
> > > 
> > > This will slightly conflict with Tomeu's  patches for per-user clock
> > > constraints. It would be best if we can take this through the clk tree
> > > to fix up any conflicts
> > 
> > I had hoped to take this through the drm tree to resolve the build-time.
> > Another possibility would be for me to include the clk tree (or a subset
> > thereof) in my pull-request. That way you can still fix things up in the
> > clock tree if there are any conflicts with other work. We could make
> > that work two ways: this patch gets applied to the clk tree and I pull
> > it, or I provide a stable branch that I base my pull request on and that
> > branch can be pulled into the clk tree.
> > 
> > Yet another alternative would be to split out the clk_has_parent()
> > change from the series and not use it for now. That way we're going to
> > miss this check, but we do that anyway currently and it will only be
> > temporary until v3.21.
> > 
> > Perhaps given where we are in the release cycle the latter would make
> > the most sense for now.
> 
> Ok well let's see what Mike wants to do given that he's doing all
> the patch applying right now. I'd think that we could put this
> one patch on a different branch that we can merge into clk-next
> and you can merge into the drm tree. At least that's the typical
> workflow that usually works for everyone.

I will be sending out a pull request today, so I'm not going to include
this patch or the dependent patch. I'll pick it up again after the merge
window and see if I need to rebase it on top of Tomeu's work.

Thierry

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