linux-kernel - Re: [PATCH E 11/14] OMAP clock: track child clocks

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Date:	Fri, 30 Jan 2009 01:35:33 -0700 (MST)
From:	Paul Walmsley <paul@...an.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH E 11/14] OMAP clock: track child clocks

On Thu, 29 Jan 2009, Russell King - ARM Linux wrote:

> On Thu, Jan 29, 2009 at 03:14:01PM +0000, Russell King - ARM Linux wrote:
> > On Wed, Jan 28, 2009 at 12:27:59PM -0700, Paul Walmsley wrote:
> > > The price paid is additional runtime memory consumption - 8 bytes per
> > > clock and 16 bytes per child clock - roughly 4.5KiB on OMAP3.
> > 
> > For OMAP3, that's 222 struct clks of which 182 are children, and indeed
> > 222 * 8 + 182 * 16 gives about 4.5K.  On OMAP2, it's 140 and 136,
> > giving 140 * 8 + 136 * 16 = 3.3K.
> > 
> > Moving struct clk_child into struct clk means that its clk and flags
> > members can be deleted, making it 8 bytes in size - effectively just
> > the list_head.  We need a list_head for the 'children' as you have it.
> > So, that works out as 16 bytes per clock.  That gives 3.5K on OMAP3
> > and 2.2K on OMAP2.
> > 
> > So, by taking that alternative approach, not only do you end up using
> > less memory, but you also don't have to have the overhead of your
> > custom memory bookkeeping.
> > 
> > The other change I'd suggest is that you have one function which deals
> > with setting the parent of a clock:
> > 
> > void clk_reparent(struct clk *child, struct clk *parent)
> > {
> > 	list_del_init(&child->sibling);
> > 	if (parent)
> > 		list_add(&child->sibling, &parent->children);
> > 	child->parent = parent;
> > 
> > 	/* now do the debugfs renaming to reattach the child
> > 	   to the proper parent */
> > }
> > 
> > which is a lot simpler than your omap_clk_add_child() and omap_clk_del_child().
> > 
> > These should be in the _core_ OMAP clock code, not just in the OMAP2
> > clock code.  OMAP1 has child clocks as well as OMAP2.
> 
> And here is my version of this patch:

Thanks, I'll take a closer look at this later today.


- Paul
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