Re: [PATCH v2 2/2] fbdev/simplefb: Add support for generic power-domains

[Richard Acayan <mailingradian@gmail.com>]

Hello,

On Wed, Nov 01, 2023 at 06:20:17PM +0100, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
>
> The simple-framebuffer device tree bindings document the power-domains
> property, so make sure that simplefb supports it. This ensures that the
> power domains remain enabled as long as simplefb is active.
>
> v2: - remove unnecessary call to simplefb_detach_genpds() since that's
>       already done automatically by devres
>     - fix crash if power-domains property is missing in DT
>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/video/fbdev/simplefb.c | 93 ++++++++++++++++++++++++++++++++++
>  1 file changed, 93 insertions(+)
>
> diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
> index 18025f34fde7..fe682af63827 100644
> --- a/drivers/video/fbdev/simplefb.c
> +++ b/drivers/video/fbdev/simplefb.c
> @@ -25,6 +25,7 @@
>  #include <linux/of_clk.h>
>  #include <linux/of_platform.h>
>  #include <linux/parser.h>
> +#include <linux/pm_domain.h>
>  #include <linux/regulator/consumer.h>
>  
>  static const struct fb_fix_screeninfo simplefb_fix = {
> @@ -78,6 +79,11 @@ struct simplefb_par {
>  	unsigned int clk_count;
>  	struct clk **clks;
>  #endif
> +#if defined CONFIG_OF && defined CONFIG_PM_GENERIC_DOMAINS
> +	unsigned int num_genpds;

This is the cause of the crash that occurred on the older patch series.
The field is unsigned, a deviation from v6.6:drivers/remoteproc/imx_rproc.c.

Instead of making it signed, this version emits an error whenever the
count is negative.

> +	struct device **genpds;
> +	struct device_link **genpd_links;
> +#endif
>  #if defined CONFIG_OF && defined CONFIG_REGULATOR
>  	bool regulators_enabled;
>  	u32 regulator_count;
> @@ -432,6 +438,89 @@ static void simplefb_regulators_enable(struct simplefb_par *par,
>  static void simplefb_regulators_destroy(struct simplefb_par *par) { }
>  #endif
>  
> +#if defined CONFIG_OF && defined CONFIG_PM_GENERIC_DOMAINS
> +static void simplefb_detach_genpds(void *res)
> +{
> +	struct simplefb_par *par = res;
> +	unsigned int i = par->num_genpds;
> +
> +	if (par->num_genpds <= 1)
> +		return;
> +
> +	while (i--) {
> +		if (par->genpd_links[i])
> +			device_link_del(par->genpd_links[i]);
> +
> +		if (!IS_ERR_OR_NULL(par->genpds[i]))
> +			dev_pm_domain_detach(par->genpds[i], true);
> +	}
> +}
> +
> +static int simplefb_attach_genpds(struct simplefb_par *par,
> +				  struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	unsigned int i;
> +	int err;
> +
> +	err = of_count_phandle_with_args(dev->of_node, "power-domains",
> +					 "#power-domain-cells");
> +	if (err < 0) {
> +		dev_info(dev, "failed to parse power-domains: %d\n", err);
> +		return err;

This error path is taken when there is no power-domains property in the
device tree with err = -ENOENT.

Strangely, this does not suppress the error like the next if statement,
even though it is possible that nothing is wrong.

> +	}
> +
> +	par->num_genpds = err;
> +
> +	/*
> +	 * Single power-domain devices are handled by the driver core, so
> +	 * nothing to do here.
> +	 */
> +	if (par->num_genpds <= 1)
> +		return 0;
> +
> +	par->genpds = devm_kcalloc(dev, par->num_genpds, sizeof(*par->genpds),
> +				   GFP_KERNEL);
<snip>
> @@ -518,6 +607,10 @@ static int simplefb_probe(struct platform_device *pdev)
>  	if (ret < 0)
>  		goto error_clocks;
>  
> +	ret = simplefb_attach_genpds(par, pdev);
> +	if (ret < 0)
> +		goto error_regulators;

With the error case specified above, not specifying power-domains (which
is valid according to dtschema) causes the entire driver to fail
whenever there are no power domains in the device tree.

On google-sargo, this causes a bug where the framebuffer fails to probe:

    [    0.409290] simple-framebuffer 9c000000.framebuffer: failed to parse power-domains: -2
    [    0.409340] simple-framebuffer: probe of 9c000000.framebuffer failed with error -2