linux-kernel - Re: [PATCH 1/6] clk: sunxi: Add support for sun9i a80 usb clocks and resets

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Date:	Fri, 14 Nov 2014 09:39:17 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Chen-Yu Tsai <wens@...e.org>
Cc:	Kishon Vijay Abraham I <kishon@...com>,
	Mike Turquette <mturquette@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Hans de Goede <hdegoede@...hat.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH 1/6] clk: sunxi: Add support for sun9i a80 usb clocks and
 resets

Hi,

Sorry for the belated answer.

On Thu, Nov 06, 2014 at 05:19:24PM +0800, Chen-Yu Tsai wrote:
> On Thu, Nov 6, 2014 at 4:54 PM, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
> > On Thu, Nov 06, 2014 at 10:09:27AM +0800, Chen-Yu Tsai wrote:
> >> >> >> +static void __init sun9i_a80_usb_mod_setup(struct device_node *node)
> >> >> >> +{
> >> >> >> +     /* AHB1 gate must be enabled to access registers */
> >> >> >> +     struct clk *ahb = of_clk_get(node, 0);
> >> >> >> +
> >> >> >> +     WARN_ON(IS_ERR(ahb));
> >> >> >> +     clk_prepare_enable(ahb);
> >> >> >
> >> >> > Hmmmm. That look off.
> >> >> >
> >> >> > Why do you need the clock to be enabled all the time? Isn't the CCF
> >> >> > already taking care of enabling the parent clock whenever it needs to
> >> >> > access any register?
> >> >>
> >> >> There are also resets in the same block. That and I couldn't get it
> >> >> working without enabling the clock beforehand.
> >> >
> >> > Ah, right.
> >> >
> >> > What happens if you just enable and disable the clocks in the
> >> > reset_assert and reset_deassert right before and after accessing the
> >> > registers?
> >>
> >> That doesn't work either. I forgot to mention that most of the clock
> >> gates have the peripheral pll as their parent, not the ahb clock gate.
> >
> > Why it doesn't work? The clock needs more time to stabilize? The reset
> > line is set back in reset if the clocks are disabled?
> 
> Let me clarify, what you proposed will work for the resets.
> 
> However the clock gates won't work if we use the generic clk-gate driver.
> The problem is most of the gates don't have the ahb gate as their parent,
> but pll4 (peripheral pll). When we enable the clock, the ahb gate isn't
> its parent, and doesn't get enabled as a result. This is especially true
> for the usb phy clocks: all of them use pll4 as their parent.

I'm not sure I get this right. You mean that this USB clock needs
*both* pll4 and its AHB gates to be enabled in order to run properly?

Or that the PHY needs its AHB gate to be enabled?

Both ways, I still don't think it's the right thing to do.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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