[PATCH v8 1/1] i2c: lpi2c: use clk notifier for rate changes

[Uwe Kleine-König]

Hello Alexander,

On Wed, Jan 17, 2024 at 08:02:19AM +0100, Alexander Stein wrote:
> Am Donnerstag, 11. Januar 2024, 09:51:30 CET schrieb Uwe Kleine-König:
> > On Wed, Jan 10, 2024 at 01:05:56PM +0100, Alexander Stein wrote:
> > > +	lpi2c_imx->clk_change_nb.notifier_call = lpi2c_imx_clk_change_cb;
> > > +	ret = devm_clk_notifier_register(&pdev->dev, lpi2c_imx->clks[0].clk,
> > > +					 &lpi2c_imx->clk_change_nb);
> > > +	if (ret)
> > > +		return dev_err_probe(&pdev->dev, ret,
> > > +				     "can't register peripheral clock notifier\n");
> > > +	/*
> > > +	 * Lock the clock rate to avoid rate change between clk_get_rate() and
> > > +	 * atomic_set()
> > > +	 */
> > > +	ret = clk_rate_exclusive_get(lpi2c_imx->clks[0].clk);
> > > +	if (ret)
> > > +		return dev_err_probe(&pdev->dev, ret,
> > > +				     "can't lock I2C peripheral clock rate\n");
> > > +
> > > +	atomic_set(&lpi2c_imx->rate_per, clk_get_rate(lpi2c_imx-clks[0].clk));
> > > +	clk_rate_exclusive_put(lpi2c_imx->clks[0].clk);
> > > +	if (!atomic_read(&lpi2c_imx->rate_per))
> > > +		return dev_err_probe(&pdev->dev, -EINVAL,
> > > +				     "can't get I2C peripheral clock rate\n");
> > > +
> > 
> > If the clkrate isn't expected to actually change, you can just delay the
> > call to clk_rate_exclusive_put() until driver unbind time and not
> > register a notifier at all. The result would be more lightweight, you
> > wouldn't even need an atomic variable for .rate_per.
> 
> On imx93 I don't expect the parent clock rate to change, as each lpi2c 
> peripheral has its own dedicated root clock.
> On imx8qxp and imx8qm lpi2c has it's own "clock tree", but these clocks are 
> managed by the system controller.
> Now idea about imx95 as this one apparently uses SCMI based clock driver.
> No idea about imx7ulp, imx8ulp and imx8dxl.

Then maybe pick the easier approach and only start with a notifier when
the need arises?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |
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