linux-kernel - Re: [PATCH v2 13/19] media: sunxi: Add support for the A31 MIPI CSI-2 controller

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Message-ID: <20201202154818.bf72m2firemyc5ve@gilmour>
Date:   Wed, 2 Dec 2020 16:48:18 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-sunxi@...glegroups.com, Yong Deng <yong.deng@...ewell.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonathan Corbet <corbet@....net>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Helen Koike <helen.koike@...labora.com>,
        Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        kevin.lhopital@...mail.com
Subject: Re: [PATCH v2 13/19] media: sunxi: Add support for the A31 MIPI
 CSI-2 controller

On Wed, Dec 02, 2020 at 03:44:47PM +0100, Paul Kocialkowski wrote:
> > > +static int __maybe_unused sun6i_mipi_csi2_suspend(struct device *dev)
> > > +{
> > > +	struct sun6i_mipi_csi2_dev *cdev = dev_get_drvdata(dev);
> > > +
> > > +	clk_disable_unprepare(cdev->clk_mod);
> > > +	clk_disable_unprepare(cdev->clk_bus);
> > > +	reset_control_assert(cdev->reset);
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int __maybe_unused sun6i_mipi_csi2_resume(struct device *dev)
> > > +{
> > > +	struct sun6i_mipi_csi2_dev *cdev = dev_get_drvdata(dev);
> > > +	int ret;
> > > +
> > > +	ret = reset_control_deassert(cdev->reset);
> > > +	if (ret) {
> > > +		dev_err(cdev->dev, "failed to deassert reset\n");
> > > +		return ret;
> > > +	}
> > > +
> > > +	ret = clk_prepare_enable(cdev->clk_bus);
> > > +	if (ret) {
> > > +		dev_err(cdev->dev, "failed to enable bus clock\n");
> > > +		goto error_reset;
> > > +	}
> > > +
> > > +	ret = clk_prepare_enable(cdev->clk_mod);
> > > +	if (ret) {
> > > +		dev_err(cdev->dev, "failed to enable module clock\n");
> > > +		goto error_clk_bus;
> > > +	}
> > > +
> > > +	return 0;
> > > +
> > > +error_clk_bus:
> > > +	clk_disable_unprepare(cdev->clk_bus);
> > > +
> > > +error_reset:
> > > +	reset_control_assert(cdev->reset);
> > > +
> > > +	return ret;
> > > +}
> > 
> > I'm guessing you set the __maybe_unused attribute because you're using
> > SET_RUNTIME_PM_OPS, but what would happen if runtime_pm isn't selected?
> > It looks like you don't handle that case.
> 
> Indeed, __maybe_unused is because of the conditional definition of
> SET_RUNTIME_PM_OPS. If CONFIG_PM is not selected, then I guess the controller
> wouldn't be powered and wouldn't work. So I should definitely add a Kconfig
> dependency on PM then, right?

There's two ways we can do it. What you suggested is one, the other is
to have something like our SPI driver to call directly the resume
function if there's no runtime pm support.

Maxime

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