Date:	Tue, 24 Feb 2015 11:04:20 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel@...inux.com, sboyd@...eaurora.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 3/4] clk: Provide an always-on clock domain framework

On Mon, 23 Feb 2015, Mike Turquette wrote:

> Quoting Lee Jones (2015-02-18 08:15:00)
> > Much h/w contain clocks which if turned off would prove fatal.  The
> > only way to recover is to restart the board(s).  This driver takes
> > references to clocks which are required to be always-on in order to
> > prevent the common clk framework from trying to turn them off during
> > the clk_disabled_unused() procedure.
> > 
> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > ---
> >  drivers/clk/Makefile    |  1 +
> >  drivers/clk/clkdomain.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 64 insertions(+)
> >  create mode 100644 drivers/clk/clkdomain.c
> > 
> > diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> > index d5fba5b..d9e2718 100644
> > --- a/drivers/clk/Makefile
> > +++ b/drivers/clk/Makefile
> > @@ -3,6 +3,7 @@ obj-$(CONFIG_HAVE_CLK)          += clk-devres.o
> >  obj-$(CONFIG_CLKDEV_LOOKUP)    += clkdev.o
> >  obj-$(CONFIG_COMMON_CLK)       += clk.o
> >  obj-$(CONFIG_COMMON_CLK)       += clk-divider.o
> > +obj-$(CONFIG_COMMON_CLK)       += clkdomain.o
> >  obj-$(CONFIG_COMMON_CLK)       += clk-fixed-factor.o
> >  obj-$(CONFIG_COMMON_CLK)       += clk-fixed-rate.o
> >  obj-$(CONFIG_COMMON_CLK)       += clk-gate.o
> > diff --git a/drivers/clk/clkdomain.c b/drivers/clk/clkdomain.c
> > new file mode 100644
> > index 0000000..8c83f99
> > --- /dev/null
> > +++ b/drivers/clk/clkdomain.c
> 
> Naming is hard. I'm not sure clkdomain.c is the best expression. Maybe
> clk-alwon.c? I see ALWON used alot amongst hardware people who live in a
> world of eight-character naming limitations.

If you can have clk-fractional-divider.c in your subsystem, I'm sure
clk-always-on.c will be suitable.

> > @@ -0,0 +1,63 @@
> > +/*
> > + * Always on Clock Domain

=;-)

> > + * Copyright (C) 2015 STMicroelectronics – All Rights Reserved
> > + *
> > + * Author: Lee Jones <lee.jones@...aro.org>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; either version 2 of the License, or
> > + * (at your option) any later version.
> > + */
> > +
> > +#include <linux/clk-private.h>
> 
> If this header still existed I would berate you mercilessly. Luckily for
> you it no longer exists and only causes a compile error ;-)

Noted.

You may wish to update: Documentation/clk.txt accordingly.

> > +#include <linux/clk-provider.h>
> > +#include <linux/of_address.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +
> > +static void ao_clock_domain_hog_clock(struct platform_device *pdev, int index)
> > +{
> > +       struct device_node *np = pdev->dev.of_node;
> > +       struct clk *clk;
> > +       int ret;
> > +
> > +       clk = of_clk_get(np, index);
> > +       if (IS_ERR(clk)) {
> > +               dev_warn(&pdev->dev, "Failed get clock %s[%d]: %li\n",
> > +                        np->full_name, index, PTR_ERR(clk));
> > +               return;
> > +       }
> > +
> > +       ret = clk_prepare_enable(clk);
> > +       if (ret)
> > +               dev_warn(&pdev->dev, "Failed to enable clock: %s\n", clk->name);
> > +}
> > +
> > +static int ao_clock_domain_probe(struct platform_device *pdev)
> > +{
> > +       struct device_node *np = pdev->dev.of_node;
> > +       int nclks, i;
> > +
> > +       nclks = of_count_phandle_with_args(np, "clocks", "#clock-cells");
> 
> Minor nitpick: please use of_clk_get_parent_count. I spent a solid 5
> minutes writing that function and I need people to use it so I can get a
> return on my investment.

My middle name is RoI.  I'm on it.

> Otherwise the patch looks good. I believe that this method is targeting
> always-on clock in a production environment, which is different from the
> CLK_IGNORE_UNUSED stuff which typically is helpful while bringing up new
> hardware or dealing with a platform that has incomplete driver support.
> 
> I wonder if there is a clever way for existing clock providers
> (expressed in DT) to use this without having to create a separate node
> of clocks with the "always-on-clk-domain" flag. Possibly the common
> clock binding could declare some always-on flag that is standardized?
> Then the framework core could use this code easily. Not sure if that is
> a good idea though...

I think having both would be a good idea.  If all clocks supplied by a
provider should be left on, then a property inside the provider node
could be a good way to describe that.  In our case only some of them
are required, so I consider this concept to be better.

> > +
> > +       for (i = 0; i < nclks; i++)
> > +               ao_clock_domain_hog_clock(pdev, i);
> > +
> > +       return 0;
> > +}
> > +
> > +static const struct of_device_id ao_clock_domain_match[] = {
> > +       { .compatible = "always-on-clk-domain" },
> > +       { },
> > +};
> > +
> > +static struct platform_driver ao_clock_domain_driver = {
> > +       .probe = ao_clock_domain_probe,
> > +       .driver = {
> > +               .name = "always-on-clk-domain",
> > +               .of_match_table = ao_clock_domain_match,
> > +       },
> > +};
> > +module_platform_driver(ao_clock_domain_driver);

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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