linux-kernel - Re: [PATCH v2] clk: Do not complain about correctly set read-only muxes when assigning clock parents from device tree

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Message-ID: <1421052137.3081.4.camel@pengutronix.de>
Date:	Mon, 12 Jan 2015 09:42:17 +0100
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Mike Turquette <mturquette@...aro.org>,
	linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH v2] clk: Do not complain about correctly set read-only
 muxes when assigning clock parents from device tree

Am Freitag, den 09.01.2015, 10:51 -0800 schrieb Stephen Boyd:
> On 01/09/2015 06:50 AM, Philipp Zabel wrote:
> > Hi Stephen,
> >
> > Am Donnerstag, den 08.01.2015, 13:32 -0800 schrieb Stephen Boyd:
> > [...]
> >> Why not do this in the core? As far as I can tell other drivers could
> >> run into the same problem, no? Does this work?
> >>
> >> -----8<-------
> >>
> >> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> >> index f4963b7d4e17..3278645f4729 100644
> >> --- a/drivers/clk/clk.c
> >> +++ b/drivers/clk/clk.c
> >> @@ -1677,16 +1677,18 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
> >>  	if (!clk)
> >>  		return 0;
> >>  
> >> -	/* verify ops for for multi-parent clks */
> >> -	if ((clk->num_parents > 1) && (!clk->ops->set_parent))
> >> -		return -ENOSYS;
> >> -
> >>  	/* prevent racing with updates to the clock topology */
> >>  	clk_prepare_lock();
> >>  
> >>  	if (clk->parent == parent)
> >>  		goto out;
> >>  
> >> +	/* verify ops for for multi-parent clks */
> >> +	if ((clk->num_parents > 1) && (!clk->ops->set_parent)) {
> >> +		ret = -ENOSYS;
> >> +		goto out;
> >> +	}
> >> +
> >>  	/* check that we are allowed to re-parent if the clock is in use */
> >>  	if ((clk->flags & CLK_SET_PARENT_GATE) && clk->prepare_count) {
> >>  		ret = -EBUSY;
> > "[PATCH] clk: make set_parent succeed for any clock if the parent to be
> > set is the same as the current parent" ?
> >
> > It works, but it also changes the API, as it makes
> >    clk_set_parent(some_non_mux, its_current_parent)
> > succeed instead of return -ENOSYS.
> 
> I would think a non_mux clk would have clk->num_parents == 1, so I don't
> see how it would return -ENOSYS here. What you mention should succeed
> today. Otherwise we have a bug.

Right. In that case, I'm all for it.

regards
Philipp

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