linux-kernel - Re: [PATCH] ARM: imx6q: Add missing esai

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Date:	Thu, 9 Jan 2014 14:57:42 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Nicolin Chen <Guangyu.Chen@...escale.com>
CC:	<kernel@...gutronix.de>, <linux@....linux.org.uk>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <rob.herring@...xeda.com>,
	<pawel.moll@....com>, <mark.rutland@....com>,
	<ijc+devicetree@...lion.org.uk>, <galak@...eaurora.org>,
	<devicetree@...r.kernel.org>, <rob@...dley.net>
Subject: Re: [PATCH] ARM: imx6q: Add missing esai_ahb clock to current clock
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On Thu, Jan 09, 2014 at 11:49:41AM +0800, Nicolin Chen wrote:
> On Thu, Jan 09, 2014 at 11:58:12AM +0800, Shawn Guo wrote:
> > >  static struct clk *clk[clk_max];
> > > @@ -355,6 +355,7 @@ static void __init imx6q_clocks_init(struct device_node *ccm_node)
> > >  	clk[ecspi5]       = imx_clk_gate2("ecspi5",        "ecspi_root",        base + 0x6c, 8);
> > >  	clk[enet]         = imx_clk_gate2("enet",          "ipg",               base + 0x6c, 10);
> > >  	clk[esai]         = imx_clk_gate2("esai",          "esai_podf",         base + 0x6c, 16);
> > > +	clk[esai_ahb]     = imx_clk_gate2("esai_ahb",      "ahb",               base + 0x6c, 16);
> > 
> > Hmm, having two clocks operating on the same gate bit will get us
> > problem in clock disabling.  Clock enabling is fine, since either
> > one who calls clk_enable() first will just set the gate bit.  But in
> > case that clk_enable() is called on both clocks, and then when either
> > clock calls clk_disable(), the gate bit will be cleared and thus breaks
> > the other one that might still be in use.
> 
> Understood. But how could we handle this situation? The only way I can figure
> out is to make sure the driver open/close them at the same time, it's not a
> perfect way though.

Hmm, we generally leave the gate bit to the clock used to access
register, because usually it's the first one to be on and the last one
to be off.

Shawn

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