From mboxrd@z Thu Jan  1 00:00:00 1970
From: s.hauer@pengutronix.de (Sascha Hauer)
Date: Mon, 13 Dec 2010 16:41:42 +0100
Subject: [RFC] i.MX clock support
In-Reply-To: <20101213150120.GE26210@pengutronix.de>
References: <20101213102538.GB6017@pengutronix.de>
	<20101213150120.GE26210@pengutronix.de>
Message-ID: <20101213154142.GP6017@pengutronix.de>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Dec 13, 2010 at 04:01:20PM +0100, Uwe Kleine-K?nig wrote:
> Hi Sascha,
> 
> On Mon, Dec 13, 2010 at 11:25:38AM +0100, Sascha Hauer wrote:
> > I am not willing to accept patches for adding i.MX50 support in the mess
> > we currently have. These patches offer a way to cleanup the clock support
> > and the i.MX50 may be a good test bed for an implementation without
> > old cruft to worry about. That said the following patch is not set in
> > stone, it's a request for comments and I'm of course open to other
> > suggestions, but it's clear that we have to do something.
> Full ack.
> 
> > +#define to_clk_divider(clk) (container_of(clk, struct clk_divider, clk))
> > +
> > +static unsigned long clk_divider_get_rate(struct clk *clk)
> > +{
> > +	struct clk_divider *divider = to_clk_divider(clk);
> > +
> > +	unsigned long rate = clk_get_rate(divider->parent);
> > +	unsigned int div = 1;
> > +
> > +	if (divider->reg) {
> > +		div = readl(divider->reg) >> divider->shift;
> > +		div &= (1 << divider->width) - 1;
> > +		div++;
> > +	}
> > +
> > +	return rate / div / divider->div * divider->mult;
> Maybe you need to spend more effort to exactness e.g. by using
> DIV_ROUND_CLOSEST and/or reordering?
> (You didn't describe div and mult in struct clk_divider (below), so this
> is a bit guess work for me here.)

Ok, this needs some work. My original idea was to have seperate fixed
dividers and configurable dividers. Then I decided to combine these into
one divider. The end result was a mixure of both. We have a struct
clk_divider_fixed, which is described but unused.

> 
> > +}
> > +
> > +static long clk_divider_round_rate(struct clk *clk, unsigned long rate)
> > +{
> > +	struct clk_divider *divider = to_clk_divider(clk);
> > +	unsigned long parent_rate = clk_get_rate(divider->parent);
> > +	unsigned int max_div, div;
> > +
> > +	if (rate > parent_rate)
> > +		return parent_rate;
> > +
> > +	max_div = 1 << divider->width;
> > +
> > +	div = parent_rate / rate;
> > +	div = max(div, max_div);
> > +
> > +	return parent_rate / div / divider->div * divider->mult;
> ditto
> 
> > +}
> > +
> > +static int clk_divider_set_rate(struct clk *clk, unsigned long rate)
> > +{
> > +	struct clk_divider *divider = to_clk_divider(clk);
> > +	unsigned long parent_rate = clk_get_rate(divider->parent);
> > +	unsigned int max_div, div;
> > +	u32 val;
> > +
> > +	parent_rate /= divider->div;
> > +	parent_rate *= divider->mult;
> > +
> > +	if (rate > parent_rate)
> > +		rate = parent_rate;
> > +
> > +	max_div = 1 << divider->width;
> > +
> > +	div = parent_rate / rate;
> > +
> > +	div = max(div, max_div);
> > +	div--;
> > +
> > +	val = readl(divider->reg);
> > +	val &= ~(((1 << divider->width) - 1) << divider->shift);
> > +	val |= div << divider->shift;
> > +	writel(val, divider->reg);
> > +
> > +	return 0;
> You could spend more efforts here, but I think this is OK for now.
> 
> > [...]
> > +struct clk_ops clk_multiplexer_ops = {
> > +	.enable = clk_parent_enable,
> > +	.disable = clk_parent_disable,
> > +	.get_rate = clk_parent_get_rate,
> > +	.round_rate = clk_parent_round_rate,
> > +	.set_rate = clk_parent_set_rate,
> Oh, this might have surprising effects if the parent is "public".
> Is this intended?

I have no idea what the best way is here. We could remove it and wait
if somebody comes up with a good reason to add it again.

Sascha

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