linux-kernel - Re: [PATCH RFC RFT 3/3] clk: introduce CLK_ENABLE_HAND

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Date:	Tue, 11 Aug 2015 10:09:28 -0700
From:	Michael Turquette <mturquette@...libre.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"Maxime Coquelin" <maxime.coquelin@...com>
Cc:	"Lee Jones" <lee.jones@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-clk@...r.kernel.org, "Stephen Boyd" <sboyd@...eaurora.org>,
	"Maxime Ripard" <maxime.ripard@...e-electrons.com>,
	"Sascha Hauer" <s.hauer@...gutronix.de>
Subject: Re: [PATCH RFC RFT 3/3] clk: introduce CLK_ENABLE_HAND_OFF flag

Quoting Geert Uytterhoeven (2015-08-11 03:11:05)
> Hi Maxime,
> 
> On Tue, Aug 11, 2015 at 12:02 PM, Maxime Coquelin
> <maxime.coquelin@...com> wrote:
> > How can we pass CLK_ENABLE_HAND_OFF flag to a specific clock on STi
> > platform?
> 
> Add the flag to the relevant clocks in the C code, e.g. in
> clk_register_flexgen():
> 
>         if (!strcmp(name, "clk-icn-cpu"))
>                 init.flags |= CLK_ENABLE_HAND_OFF;
> 
> > Could we imagine having a kind of "clocks-enable-hand-off" property we could
> > use in our clock controller DT node?
> 
> You can imagine doing "flex_flags |= CLK_ENABLE_HAND_OFF" in
> st_of_flexgen_setup(), depending on the presence of such a property.

This is precisely what Lee is trying to avoid. The would constitute a
hand-rolled, open-code, gather-and-mark exercise that drivers would have
to re-invent each time. (rough paraphrase of what Lee said)

I think that we can come up with a reasonable DT wrapper around the
flag. I will be ecstatic if we can agree that the meaning of the flag
can be tweaked just a bit to mean, "prevent this critical clock from
being disabled, as it was enabled out of reset or by the bootloader,
until a driver claims it and calls clk_prepare_enable".

Then everyone should be happy.

Regards,
Mike

> 
> However, not disabling clocks is a software policy, not a hardware description,
> so IMHO it doesn't belong in DT.
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
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