Re: [PATCH v6 2/3] media: ov8856: Add devicetree support

From: Sakari Ailus <sakari.ailus@iki.fi>
To: Marco Felsch <m.felsch@pengutronix.de>
Cc: Robert Foss <robert.foss@linaro.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Maxime Ripard <maxime@cerno.tech>,
	linux-media@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Dongchun Zhu <dongchun.zhu@mediatek.com>,
	Fabio Estevam <festevam@gmail.com>,
	Tomasz Figa <tfiga@chromium.org>
Subject: Re: [PATCH v6 2/3] media: ov8856: Add devicetree support
Date: Thu, 30 Apr 2020 13:20:18 +0300	[thread overview]
Message-ID: <20200430102018.GI867@valkosipuli.retiisi.org.uk> (raw)
In-Reply-To: <20200430101157.GD2188@pengutronix.de>

On Thu, Apr 30, 2020 at 12:11:57PM +0200, Marco Felsch wrote:
> On 20-04-30 12:59, Sakari Ailus wrote:
> > Hi Marco,
> > 
> > On Thu, Apr 30, 2020 at 11:53:32AM +0200, Marco Felsch wrote:
> > > Hi Sakari,
> > > 
> > > On 20-04-30 12:45, Sakari Ailus wrote:
> > > > Hi Marco,
> > > > 
> > > > On Thu, Apr 30, 2020 at 11:35:24AM +0200, Marco Felsch wrote:
> 
> ...
> 
> > > > > > -	if (mclk != OV8856_MCLK) {
> > > > > > -		dev_err(dev, "external clock %d is not supported", mclk);
> > > > > > -		return -EINVAL;
> > > > > > +	if (!is_acpi_node(fwnode)) {
> > > > > > +		ov8856->xvclk = devm_clk_get(dev, "xvclk");
> > > > > > +		if (IS_ERR(ov8856->xvclk)) {
> > > > > > +			dev_err(dev, "could not get xvclk clock (%pe)\n",
> > > > > > +					ov8856->xvclk);
> > > > > > +			return PTR_ERR(ov8856->xvclk);
> > > > > > +		}
> > > > > > +
> > > > > > +		clk_set_rate(ov8856->xvclk, xvclk_rate);
> > > > > > +		xvclk_rate = clk_get_rate(ov8856->xvclk);
> > > > > >  	}
> > > > > 
> > > > > Why do we handle the clock only in DT case? Is there a problem with the
> > > > > clock handling and ACPI?
> > > > 
> > > > Not really, it's just that ACPI does not provide an interface to the clocks
> > > > as such.
> > > 
> > > But you will get a clk by devm_clk_get()?
> > 
> > No, because ACPI does not expose one to drivers. Effectively the entire
> > power sequences are implemented in ACPI, not in the driver.
> > 
> 
> Ah okay, thanks for the explanation. I'm really not into the ACPI
> stuff.. So this means the __power_off / power_on should only be done if
> we are using DT's?

Correct. That's why it bails out early. It could be yet earlier though,
without doing anything.

-- 
Sakari Ailus