linux-kernel - Re: [RFC] Common clock framework for external clock generators

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Message-ID: <20120513122946.GD706@sirena.org.uk>
Date:	Sun, 13 May 2012 13:29:46 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Sebastian Hesselbarh <sebastian.hesselbarth@...glemail.com>
Cc:	linux-kernel@...r.kernel.org, mturquette@...com
Subject: Re: [RFC] Common clock framework for external clock generators

On Thu, May 10, 2012 at 03:11:55AM +0200, Sebastian Hesselbarh wrote:

Always CC maintainers on mails, things get lost on high volume lists.

> I recently read about the newly introduced common clock framework (ccf)
> and wondered if this could be also used for external, e.g. i2c attached,
> clock generators.

Yes, it should be able to be used for this.  I've been posting a driver
for the wm831x PMICs for quite some considerable time.

> static inline u8 si5351_reg_read(struct si5351_driver_data *data, u8 addr)
> {
> 	return (u8)i2c_smbus_read_byte_data(data->client, addr);
> }

I'd suggest using regmap for the cache support (which helps with
read/modify/write cycles) and because...

> static int si5351_xtal_enable(struct clk_hw *hw)
> {
> 	struct si5351_driver_data *sidata = 
> 		container_of(hw, struct si5351_driver_data, hw_xtal);
> 	u8 reg;
> 
> 	reg = si5351_reg_read(sidata, SI5351_FANOUT_ENABLE);
> 	reg |= SI5351_XTAL_ENABLE;
> 	si5351_reg_write(sidata, SI5351_FANOUT_ENABLE, reg);
> 	return 0;
> }

...we should be able to factor things like this out of the drivers using
regmap (we've been getting some great results doing that for regulator
over this release).

> static const struct clk_ops si5351_xtal_ops = {
> 	.enable = si5351_xtal_enable,
> 	.disable = si5351_xtal_disable,

These should be prepare() and unprepare() - enable() and disable() are
called from atomic context so you can't do I2C I/O.

> static u8 si5351_clkout_get_parent(struct clk_hw *hw)
> {
> 	struct si5351_driver_data *sidata = si5351_clkout_get_data(hw);
> 	return 0;
> }

If we need empty functions like this we should fix the framework.

> 	sidata = kzalloc(sizeof(struct si5351_driver_data), GFP_KERNEL);
> 	if (sidata == NULL) {
> 		dev_err(&client->dev, "unable to allocate driver data\n");
> 		return -ENOMEM;
> 	}

devm_kzalloc().
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