linux-kernel - Re: [PATCH] drm/tidss: Power up attached PM domains on probe

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Message-ID: <bmemgnq3emddmjsho3c3h4cj2fyyyp3xll73ozpsxxmxxcr3bn@lffrmuqqpbl3>
Date:   Mon, 9 Oct 2023 11:23:06 +0200
From:   Maxime Ripard <mripard@...nel.org>
To:     Devarsh Thakkar <devarsht@...com>
Cc:     jyri.sarha@....fi, tomi.valkeinen@...asonboard.com,
        airlied@...il.com, daniel@...ll.ch,
        maarten.lankhorst@...ux.intel.com, tzimmermann@...e.de,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        praneeth@...com, nm@...com, vigneshr@...com, a-bhatia1@...com,
        j-luthra@...com, r-ravikumar@...com, j-choudhary@...com
Subject: Re: [PATCH] drm/tidss: Power up attached PM domains on probe

Hi Devarsh,

On Mon, Oct 09, 2023 at 01:20:18PM +0530, Devarsh Thakkar wrote:
> Some SoC's such as AM62P have dedicated power domains
> for OLDI which need to be powered on separetely along
> with display controller.
> 
> So during driver probe, power up all attached PM domains
> enumerated in devicetree node for DSS.
> 
> This also prepares base to add display support for AM62P.
> 
> Signed-off-by: Devarsh Thakkar <devarsht@...com>
> ---
>  drivers/gpu/drm/tidss/tidss_drv.c | 76 +++++++++++++++++++++++++++++++
>  drivers/gpu/drm/tidss/tidss_drv.h |  5 ++
>  2 files changed, 81 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_drv.c b/drivers/gpu/drm/tidss/tidss_drv.c
> index 4d063eb9cd0b..a703a27d17bf 100644
> --- a/drivers/gpu/drm/tidss/tidss_drv.c
> +++ b/drivers/gpu/drm/tidss/tidss_drv.c
> @@ -8,6 +8,7 @@
>  #include <linux/of.h>
>  #include <linux/module.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/pm_domain.h>
>  
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_atomic_helper.h>
> @@ -114,6 +115,72 @@ static const struct drm_driver tidss_driver = {
>  	.minor			= 0,
>  };
>  
> +static int tidss_detach_pm_domains(struct tidss_device *tidss)
> +{
> +	int i;
> +
> +	if (tidss->num_domains <= 1)
> +		return 0;
> +
> +	for (i = 0; i < tidss->num_domains; i++) {
> +		if (tidss->pd_link[i] && !IS_ERR(tidss->pd_link[i]))
> +			device_link_del(tidss->pd_link[i]);
> +		if (tidss->pd_dev[i] && !IS_ERR(tidss->pd_dev[i]))
> +			dev_pm_domain_detach(tidss->pd_dev[i], true);
> +		tidss->pd_dev[i] = NULL;
> +		tidss->pd_link[i] = NULL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int tidss_attach_pm_domains(struct tidss_device *tidss)
> +{
> +	struct device *dev = tidss->dev;
> +	int i;
> +	int ret;
> +	struct platform_device *pdev = to_platform_device(dev);
> +	struct device_node *np = pdev->dev.of_node;
> +
> +	tidss->num_domains = of_count_phandle_with_args(np, "power-domains",
> +							"#power-domain-cells");
> +	if (tidss->num_domains <= 1) {
> +		dev_dbg(dev, "One or less power domains, no need to do attach domains\n");
> +		return 0;
> +	}
> +
> +	tidss->pd_dev = devm_kmalloc_array(dev, tidss->num_domains,
> +					   sizeof(*tidss->pd_dev), GFP_KERNEL);
> +	if (!tidss->pd_dev)
> +		return -ENOMEM;
> +
> +	tidss->pd_link = devm_kmalloc_array(dev, tidss->num_domains,
> +					    sizeof(*tidss->pd_link), GFP_KERNEL);
> +	if (!tidss->pd_link)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < tidss->num_domains; i++) {
> +		tidss->pd_dev[i] = dev_pm_domain_attach_by_id(dev, i);
> +		if (IS_ERR(tidss->pd_dev[i])) {
> +			ret = PTR_ERR(tidss->pd_dev[i]);
> +			goto fail;
> +		}
> +
> +		tidss->pd_link[i] = device_link_add(dev, tidss->pd_dev[i],
> +						    DL_FLAG_STATELESS |
> +						    DL_FLAG_PM_RUNTIME | DL_FLAG_RPM_ACTIVE);
> +		if (!tidss->pd_link[i]) {
> +			ret = -EINVAL;
> +			goto fail;
> +		}
> +	}
> +
> +	return 0;
> +fail:
> +	tidss_detach_pm_domains(tidss);
> +	return ret;
> +}

My understanding is that this will be done automatically at probe time.
Why do we need to roll our own there? A comment on top of the function
and the commit log would help.

Thanks!
Maxime

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