Re: [PATCH v3 4/6] thermal: sun8i: add syscon register access code - Chen-Yu Tsai

From: Chen-Yu Tsai <wens@csie.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Andre Przywara <andre.przywara@arm.com>,
	Vasily Khoruzhick <anarsoul@gmail.com>,
	 Yangtao Li <tiny.windzz@gmail.com>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	 Samuel Holland <samuel@sholland.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	 Daniel Lezcano <daniel.lezcano@linaro.org>,
	Zhang Rui <rui.zhang@intel.com>,
	 Lukasz Luba <lukasz.luba@arm.com>,
	Rob Herring <robh+dt@kernel.org>,
	 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	 Martin Botka <martin.botka@somainline.org>,
	Bob McChesney <bob@electricworry.net>,
	 linux-pm@vger.kernel.org, devicetree@vger.kernel.org,
	 linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev
Subject: Re: [PATCH v3 4/6] thermal: sun8i: add syscon register access code
Date: Tue, 28 Nov 2023 15:50:51 +0800	[thread overview]
Message-ID: <CAGb2v66YpYBS78C7H-O3zef2NTs+7=ec3A7jrZ+DxjYEyBmWxQ@mail.gmail.com> (raw)
In-Reply-To: <ddceb30f-1778-4312-af91-97813fe3c6fb@linaro.org>

On Tue, Nov 28, 2023 at 3:43 PM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>
> On 28/11/2023 01:58, Andre Przywara wrote:
> >
> > +static struct regmap *sun8i_ths_get_syscon_regmap(struct device_node *node)
> > +{
> > +     struct device_node *syscon_node;
> > +     struct platform_device *syscon_pdev;
> > +     struct regmap *regmap = NULL;
> > +
> > +     syscon_node = of_parse_phandle(node, "syscon", 0);
>
> Nope. For the 100th time, this cannot be generic.
>
> > +     if (!syscon_node)
> > +             return ERR_PTR(-ENODEV);
> > +
> > +     syscon_pdev = of_find_device_by_node(syscon_node);
> > +     if (!syscon_pdev) {
> > +             /* platform device might not be probed yet */
> > +             regmap = ERR_PTR(-EPROBE_DEFER);
> > +             goto out_put_node;
> > +     }
> > +
> > +     /* If no regmap is found then the other device driver is at fault */
> > +     regmap = dev_get_regmap(&syscon_pdev->dev, NULL);
> > +     if (!regmap)
> > +             regmap = ERR_PTR(-EINVAL);
>
> Aren't you open-coding existing API to get regmap from syscon?

Not really. This is to get a regmap exported by the device. Syscon's regmap
is not tied to the device at all.

With this scheme a device to could export just enough registers for the
consumer to use, instead of the whole address range.

We do this in the R40 clock controller as well, which has some bits that
tweak the ethernet controllers RGMII delay...

ChenYu