linux-kernel - Re: [PATCH V3 3/3] ARM: clk-imx6q: Add missing lvds and anaclk clock to the clock tree

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Date:	Mon, 18 Aug 2014 14:06:07 +0800
From:	Shawn Guo <shawn.guo@...escale.com>
To:	Shengjiu Wang <shengjiu.wang@...escale.com>
CC:	<kernel@...gutronix.de>, <linux@....linux.org.uk>,
	<robh+dt@...nel.org>, <pawel.moll@....com>, <mark.rutland@....com>,
	<ijc+devicetree@...lion.org.uk>, <galak@...eaurora.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 3/3] ARM: clk-imx6q: Add missing lvds and anaclk clock
 to the clock tree

On Mon, Aug 11, 2014 at 11:09:36AM +0800, Shengjiu Wang wrote:
> On Sat, Aug 09, 2014 at 09:58:42PM +0800, Shawn Guo wrote:
> > On Fri, Aug 08, 2014 at 03:02:49PM +0800, Shengjiu Wang wrote:
> > > @@ -176,8 +182,12 @@ static void __init imx6q_clocks_init(struct device_node *ccm_node)
> > >  	 * the "output_enable" bit as a gate, even though it's really just
> > >  	 * enabling clock output.
> > >  	 */
> > > -	clk[IMX6QDL_CLK_LVDS1_GATE] = imx_clk_gate("lvds1_gate", "lvds1_sel", base + 0x160, 10);
> > > -	clk[IMX6QDL_CLK_LVDS2_GATE] = imx_clk_gate("lvds2_gate", "lvds2_sel", base + 0x160, 11);
> > > +	clk[IMX6QDL_CLK_LVDS1_GATE] = imx_clk_gate2("lvds1_gate", "lvds1_sel", base + 0x160, 10);
> > > +	clk[IMX6QDL_CLK_LVDS2_GATE] = imx_clk_gate2("lvds2_gate", "lvds2_sel", base + 0x160, 11);
> > 
> > I do not think you can simply change to use imx_clk_gate2() here.  It's
> > designed for those CCGR gate clocks, each of which is controlled by two
> > bits.
> > 
> > Shawn
> >
> As Lucas Stach's suggestion, we need to do add some method for mutually exclusive clock, 
> lvds1_gate with lvds1_in, lvds2_gate with lvds2_in. I add imx_clk_gate2_exclusive() function in clk-gate2.c.
> So I change imx_clk_gate() to imx_clk_gate2() here.
> As you said, this is not good solution.

It's not just a "not good" solution but wrong and broken one.  The net
result of that is if you call clk_enable() on lvds1_gate, both bit 10
and 11 will be set.

> So I need your suggestion, how can I do?

I guess we will need a new clock type to handle such mutually exclusive
clocks, rather than patching clk-gate2.

> First, is it allowable that to add imx_clk_gate2_exclusive() function, is there a more better way?

Again, this is completely wrong.

> second, or should I change the clk-gate.c to add exclusive control?

If such mutually exclusive clocks are somehow common across different
clock controllers, we can propose to change clk-gate.c for handling
them.  But I'm not sure this is a common case.

Shawn
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