Re: [PATCH 5/6] media: sun4i: Add H3 deinterlace driver

Jernej Škrabec
2019-09-14T06:42:32Z

Hi!

Dne četrtek, 12. september 2019 ob 22:26:47 CEST je Maxime Ripard napisal(a):
> Hi,
>
> On Thu, Sep 12, 2019 at 07:51:31PM +0200, Jernej Skrabec wrote:
> > + dev->regmap = devm_regmap_init_mmio(dev->dev, dev->base,
> > +
&deinterlace_regmap_config);
> > + if (IS_ERR(dev->regmap)) {
> > + dev_err(dev->dev, "Couldn't create deinterlace
regmap\n");
> > +
> > + return PTR_ERR(dev->regmap);
> > + }
> > +
> > + ret = clk_prepare_enable(dev->bus_clk);
> > + if (ret) {
> > + dev_err(dev->dev, "Failed to enable bus clock\n");
> > +
> > + return ret;
> > + }
>
> Do you need to keep the bus clock enabled all the time? Usually, for
> the SoCs that have a reset line, you only need it to read / write to
> the registers, not to have the controller actually running.
>
> If you don't, then regmap_init_mmio_clk will take care of that for
> you.
>
> > + clk_set_rate(dev->mod_clk, 300000000);
> > +
> > + ret = clk_prepare_enable(dev->mod_clk);
> > + if (ret) {
> > + dev_err(dev->dev, "Failed to enable mod clock\n");
> > +
> > + goto err_bus_clk;
> > + }
> > +
> > + ret = clk_prepare_enable(dev->ram_clk);
> > + if (ret) {
> > + dev_err(dev->dev, "Failed to enable ram clock\n");
> > +
> > + goto err_mod_clk;
> > + }
> > +
> > + ret = reset_control_reset(dev->rstc);
> > + if (ret) {
> > + dev_err(dev->dev, "Failed to apply reset\n");
> > +
> > + goto err_ram_clk;
> > + }
>
> This could be moved to a runtime_pm hook, with get_sync called in the
> open. That way you won't leave the device powered on if it's unused.

Currently I'm looking at sun4i_csi.c as an example of runtime ops, but it
seems a bit wrong to have suspend and resume function marked with
__maybe_unused because they are the only functions which enable needed clocks.
If CONFIG_PM is not enabled, then this driver simply won't work, because
clocks will never get enabled. I guess I can implement runtime pm ops in the
same way and add additional handling when CONFIG_PM is not enabled, right?

BTW, which callback is get_sync? I don't see it in dev_pm_ops. I suppose I
need only runtime_suspend and runtime_resume.

Off topic: sun6i_csi.c includes linux/pm_runtime.h but it doesn't have any kind
of power management as far as I can see.

Best regards,
Jernej

>
> > +struct deinterlace_dev {
> > + struct v4l2_device v4l2_dev;
> > + struct video_device vfd;
> > + struct device *dev;
> > + struct v4l2_m2m_dev *m2m_dev;
> > +
> > + /* Device file mutex */
> > + struct mutex dev_mutex;
> > +
> > + void __iomem *base;
> > + struct regmap *regmap;
>
> Do you need to store the base address in that structure if you're
> using the regmap?
>
> Maxime