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

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Message-ID: <20140109075827.GP6750@pengutronix.de>
Date:	Thu, 9 Jan 2014 08:58:28 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Nicolin Chen <Guangyu.Chen@...escale.com>
Cc:	Shawn Guo <shawn.guo@...aro.org>, 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 03:41:38PM +0800, Nicolin Chen wrote:
> 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?

Please wait for Mikes input or let's look how a proper solution can look
like. I've already seen the case that a single bit controls multiple
clocks. Hacking around this issue each time is not a solution.

Sascha

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