linux-kernel - Re: [PATCH v8 3/3] pmdomain: mediatek: Use OF-specific regulator API to get power domain supply

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Message-ID: <e3eabcc4-1174-4a58-a084-d37467f63ced@collabora.com>
Date: Thu, 26 Sep 2024 10:48:56 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Chen-Yu Tsai <wenst@...omium.org>, Ulf Hansson <ulf.hansson@...aro.org>,
 Matthias Brugger <matthias.bgg@...il.com>, Mark Brown <broonie@...nel.org>
Cc: devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org, Douglas Anderson <dianders@...omium.org>,
 Johan Hovold <johan@...nel.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Pablo Sun <pablo.sun@...iatek.com>, Macpaul Lin <macpaul.lin@...iatek.com>,
 Sebastian Reichel <sebastian.reichel@...labora.com>
Subject: Re: [PATCH v8 3/3] pmdomain: mediatek: Use OF-specific regulator API
 to get power domain supply

Il 25/09/24 11:38, Chen-Yu Tsai ha scritto:
> The MediaTek power domain driver contains a hack that assigns the device
> node of the power domain to the struct device of the power domain
> controller in order to use the devres regulator API.
> 
> Now that there is a proper OF-specific regulator API, and even a devres
> version, replace the hack with proper code.
> 
> This change is incompatible with incomplete device trees. Instead of
> assigning the dummy regulator in cases where the power domain requires
> a supply but the device tree does not provide one, the driver will just
> error out. This will be seen on the MT8390 EVK, which is missing
> supplies for the IMG_VCORE and CAM_VCORE domains. And likely all the
> MediaTek EVBs, which have no power domain supplies specified. This is
> however the correct behavior. If the power domain's supply is missing,
> then it should not work. Relying on other parts of the system to keep
> the unattached regulator enabled is likely to break in ways less easier
> to understand.
> 

Breaking something that was "working" (not really working though) before is a
hard thing to justify, but I feel like this is one of the cases in which we
have to swallow the pill.

This is a hack that I've always been angry about, and causing all sorts of
random issues on MediaTek SoCs from time to time... that was fixed multiple
times by hacking the previous hack which was needed for this hack to still
work in a way or another.

I am tempted to give you a R-b right now, but let me carefully test this on
multiple devices before that.

Meanwhile, I just wanted to say that I agree with you about this commit and
wanted to give a bit more context to people reading "this breaks things" so
that they can understand what's going on (and that we're not crazy! ..or at
least, not *that* much :-P).

Cheers,
Angelo

> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
> ---
> Changes since v7:
> - New patch
> 
> The other option is to follow what Rockchip will be doing: getting the
> regulator supply upon first use / enable [1]. This will result in less
> breakage: only the power domain that is missing its supplies will fail
> to be attached.
> 
> [1] https://lore.kernel.org/all/20240919091834.83572-6-sebastian.reichel@collabora.com/
> ---
>   drivers/pmdomain/mediatek/mtk-pm-domains.c | 12 +-----------
>   1 file changed, 1 insertion(+), 11 deletions(-)
> 
> diff --git a/drivers/pmdomain/mediatek/mtk-pm-domains.c b/drivers/pmdomain/mediatek/mtk-pm-domains.c
> index 88406e9ac63c..3580913f25d3 100644
> --- a/drivers/pmdomain/mediatek/mtk-pm-domains.c
> +++ b/drivers/pmdomain/mediatek/mtk-pm-domains.c
> @@ -353,7 +353,6 @@ generic_pm_domain *scpsys_add_one_domain(struct scpsys *scpsys, struct device_no
>   {
>   	const struct scpsys_domain_data *domain_data;
>   	struct scpsys_domain *pd;
> -	struct device_node *root_node = scpsys->dev->of_node;
>   	struct device_node *smi_node;
>   	struct property *prop;
>   	const char *clk_name;
> @@ -388,16 +387,7 @@ generic_pm_domain *scpsys_add_one_domain(struct scpsys *scpsys, struct device_no
>   	pd->scpsys = scpsys;
>   
>   	if (MTK_SCPD_CAPS(pd, MTK_SCPD_DOMAIN_SUPPLY)) {
> -		/*
> -		 * Find regulator in current power domain node.
> -		 * devm_regulator_get() finds regulator in a node and its child
> -		 * node, so set of_node to current power domain node then change
> -		 * back to original node after regulator is found for current
> -		 * power domain node.
> -		 */
> -		scpsys->dev->of_node = node;
> -		pd->supply = devm_regulator_get(scpsys->dev, "domain");
> -		scpsys->dev->of_node = root_node;
> +		pd->supply = devm_of_regulator_get_optional(scpsys->dev, node, "domain");
>   		if (IS_ERR(pd->supply))
>   			return dev_err_cast_probe(scpsys->dev, pd->supply,
>   				      "%pOF: failed to get power supply.\n",