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

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Message-ID: <20140109074137.GA14809@MrMyself>
Date:	Thu, 9 Jan 2014 15:41:38 +0800
From:	Nicolin Chen <Guangyu.Chen@...escale.com>
To:	Shawn Guo <shawn.guo@...aro.org>
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
 tree

On Thu, Jan 09, 2014 at 02:57:42PM +0800, Shawn Guo wrote:
> 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.

Then we should attach CLK_IGNORE_UNUSED to clk[esai] since clk[esai_ahb] is
the clock used to access memory, shouldn't we?

Thank you.
Nicolin



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