linux-kernel - Re: [PATCH 2/2] i2c: designware: Add support for a bus clock

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Date:   Tue, 17 Jul 2018 17:47:19 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Phil Edworthy <phil.edworthy@...esas.com>,
        Simon Horman <horms@...ge.net.au>
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH 2/2] i2c: designware: Add support for a bus clock

On Tue, 2018-07-17 at 14:40 +0000, Phil Edworthy wrote:
> Hi Andy,
> 
> On 17 July 2018 15:19, Andy Shevchenko wrote:
> > On Tue, 2018-07-17 at 12:42 +0000, Phil Edworthy wrote:
> > 
> > > > While your point sounds valid (don't remember how clk_get() is
> > > > implemented), NULL is also OK to have.
> > > 
> > > Ok as in there is no bus clock, right?
> > > So it should be:
> > >  if (!IS_ERR_OR_NULL (dev->busclk))
> > 
> > Nope, NULL is no error case for optional clock.
> 
> I must be missing something here...

See how clk_prepare_enable() is implemented.

> I agree that NULL for an optional clock is not an error. However, the 
> code above is now:
> +	if (prepare) {
> +		/* Optional bus clock */

> +		if (!IS_ERR_OR_NULL(dev->busclk)) {

Check for NULL is redundant.

> +			ret = clk_prepare_enable(dev->busclk);
> +			if (ret)
> +				return ret;
> +		}
> +
>  		return clk_prepare_enable(dev->clk);
> +	}
> 
> So, if you have a valid busclk, it gets enabled, otherwise it is
> left alone.


-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy