Re: [PATCH v4 7/8] soc: starfive: Add socinfo driver for JHB100 SoC

[Changhuang Liang]

Hi, Conor

> Thanks for the review.
> 
> > On Mon, Aug 17, 2026 at 01:27:08AM +0000, Changhuang Liang wrote:
> > > Hi, Conor
> > >
> > > Thanks for the review.
> > >
> > > > On Fri, Aug 14, 2026 at 01:13:38AM +0000, Changhuang Liang wrote:
> > > > > Hi,Conor
> > > > >
> > > > > Thanks for the review.
> > > > >
> > > > > > On Thu, Aug 13, 2026 at 08:10:12AM +0000, Changhuang Liang
> wrote:
> > > > > > > Hi ,Conor
> > > > > > >
> > > > > > > Thanks for the review.
> > > > > > >
> > > > > > > > On Wed, Aug 12, 2026 at 10:37:16AM +0000, Changhuang Liang
> > > > wrote:
> > > > > > > > > Hi, Conor
> > > > > > > > >
> > > > > > > > > Thanks for the review.
> > > > > > > > >
> > > > > > > > > > On Tue, Aug 11, 2026 at 05:36:19AM +0000, Changhuang
> > > > > > > > > > Liang
> > > > wrote:
> > > > > > > > > >
> > > > > > > > > > > > On Sat, Aug 08, 2026 at 06:50:53PM -0700,
> > > > > > > > > > > > Changhuang Liang
> > > > > > wrote:
> > > > > > > > > >
> > > > > > > > > > > > > +static int __init starfive_socinfo_init(void) {
> > > > > > > > > > > > > +	struct soc_device_attribute *attrs;
> > > > > > > > > > > > > +	struct soc_device *soc_dev;
> > > > > > > > > > > > > +	const char *machine = NULL;
> > > > > > > > > > > > > +	struct device_node *np;
> > > > > > > > > > > > > +	struct regmap *regmap;
> > > > > > > > > > > > > +	char rev_char;
> > > > > > > > > > > > > +	u32 rev_id;
> > > > > > > > > > > > > +	int ret;
> > > > > > > > > > > > > +
> > > > > > > > > > > > > +	np = of_find_compatible_node(NULL, NULL,
> > > > > > > > > > > > > +"starfive,jhb100-sys0-syscon");
> > > > > > > > > > > >
> > > > > > > > > > > > Remind me again why this is not just probed as an
> > > > > > > > > > > > mfd cell from the syscon driver?
> > > > > > > > > > > >
> > > > > > > > > > > > (Hint: please put this info in the commit message).
> > > > > > > > > > >
> > > > > > > > > > > The discussion result with Krzysztof at that time is
> > > > > > > > > > > recorded
> > here:
> > > > > > > > > > > https://lore.kernel.org/all/20260405-strong-watchful
> > > > > > > > > > > -m
> > > > > > > > > > > armo
> > > > > > > > > > > t-fd
> > > > > > > > > > > fad6
> > > > > > > > > > > @quo
> > > > > > > > > > > ll/
> > > > > > > > > > >
> > > > > > > > > > > One register should not be treated as a separate device
> node.
> > > > > > > > > >
> > > > > > > > > > That's a different question. In the case of an mfd
> > > > > > > > > > cell probed from the syscon driver there would be no
> > > > > > > > > > devicetree modifications required compared to what you
> > > > > > > > > > have
> > now. e.g.
> > > > > > > > > > sg2044-topsys.c
> > > > > > > > >
> > > > > > > > > This seems feasible, and I can introduce this
> > > > > > > > > modification in the next
> > > > > > > > version.
> > > > > > > >
> > > > > > > >
> > > > > > > > In fact, you don't even need the mfd cell, because your
> > > > > > > > driver is going to be in drivers/soc/starfive anyway? You
> > > > > > > > can just bind directly to the
> > > > > > > > sys0 syscon I think.
> > > > > > >
> > > > > > > I suddenly realized that I missed one issue:
> > > > > > > starfive,jhb100-sys0-syscon is already bound to the PLL
> > > > > > > driver by default, I
> > > > > > can't use it to bind another device anymore.
> > > > > > >
> > > > > > > which is why I used
> > > > > > >
> > > > > > > np = of_find_compatible_node(NULL, NULL,
> > > > > > > "starfive,jhb100-sys0-syscon");
> > > > > > >
> > > > > > > in jhb100-socinfo.c.
> > > > > > >
> > > > > > > So it seems the MFD cell approach isn't really feasible either?
> > > > > >
> > > > > > You could, in that case, probe the clock driver using the
> > > > > > mfd_cell like sg2044-topsys. What else other than the pll
> > > > > > controls and the soc info register is in this register region?
> > > > >
> > > > > We don't have any other drivers right now in this register region.
> > > >
> > > > I'm not asking about what's got a driver right now though, I am
> > > > wondering what else the registers in this region are for.
> > >
> > > Here are some registers related to debug functionality.
> >
> > So probably nothing else that linux will ever need?
> 
> Yes.
> 
> >
> > > > > So does that mean I can revise it to the format below:
> > > > >
> > > > > static const struct mfd_cell jhb100_sys0_subdev[] = {
> > > > > 	{
> > > > > 		.name = "jhb100-sys0-pll",
> > > > > 	},
> > > >
> > > > > 	{
> > > > > 		.name = "jhb100-socinfo",
> > > >
> > > > Why would this be needed? The driver with the mfd_cell would be
> > > > the same one that provides the soc info, no?
> > >
> > > My understanding is that one driver can only bind to one device, so
> > > the PLL driver and the socinfo driver need these two devices
> > > respectively, and thus cannot share one?
> >
> > Correct, but I am talking about the socinfo driver being the one that
> > calls
> > devm_mfd_add_devices() to create a device for the pll so that in the
> > end there are a total of two drivers, rather than create something
> > identical to sg2044-topsys.c that does nothing other than initialise two mfd
> cells.
> > May as well consolidate the mfd_cell definition and call to
> > devm_mfd_add_devices() in one file, since it would be in the same
> > directory as the socinfo driver anyway.
> 
> Okay, I will use this method.

During the process of attempting this modification, there will be accompanying changes to the PLL driver. 
The main changes include the following:

1. Addition of platform device ID table: A new platform_device_id array is introduced, enabling the driver to
be matched by device name when no OF compatible string is available.

2. Dynamic device node resolution: The driver now attempts to obtain the device node using dev_of_node(dev).
 If the device has no node of its own (as is the case when instantiated as an MFD child cell), it falls back to 
using the parent device's DT node (dev_of_node(dev->parent)). This ensures the syscon regmap can still be 
correctly retrieved.

The current initial draft of the PLL changes is generally as follows: Do you have any better suggestions on
your side?

=====================================================

	const struct jhb100_pll_match_data *match_data;
+	struct device *dev = &pdev->dev;
+	struct device_node *np;
 	struct jhb100_pll_priv *priv;
 	unsigned int idx;
 	int ret;
 
-	match_data = of_device_get_match_data(&pdev->dev);
-	if (!match_data)
-		return -EINVAL;
+	match_data = of_device_get_match_data(dev);
+	if (!match_data) {
+		const struct platform_device_id *id = platform_get_device_id(pdev);
+
+		if (!id)
+			return dev_err_probe(dev, -EINVAL, "no match data\n");
+
+		match_data = (const struct jhb100_pll_match_data *)id->driver_data;
+	}
 
 	priv = devm_kzalloc(&pdev->dev,
			    struct_size(priv, pll, match_data->num_pll),
 			    GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;
 
 	priv->match_data = match_data;
-	priv->dev = &pdev->dev;
-	priv->regmap = syscon_node_to_regmap(priv->dev->of_node);
-	if (IS_ERR(priv->regmap))
-		return PTR_ERR(priv->regmap);
+	priv->dev = dev;
+
+	/*
+	 * When instantiated as an MFD cell of the sys0 system controller this
+	 * device has no DT node of its own, so use the parent syscon node.
+	 */
+	np = dev_of_node(dev) ? : dev_of_node(dev->parent);
+	priv->regmap = syscon_node_to_regmap(np);
+	if (IS_ERR(priv->regmap))
+		return dev_err_probe(dev, PTR_ERR(priv->regmap),
+				     "failed to get syscon regmap\n");

 static const struct of_device_id jhb100_pll_match[] = {
-	{
-		.compatible = "starfive,jhb100-sys0-syscon",
-		.data = &jhb100_sys0_pll,
-	},
 	{
 		.compatible = "starfive,jhb100-per0-syscon",
 		.data = &jhb100_per0_pll,
 	},
 	{
 		.compatible = "starfive,jhb100-per1-syscon",
 		.data = &jhb100_per1_pll,
 	},
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, jhb100_pll_match);
 
+static const struct platform_device_id jhb100_pll_ids[] = {
+	{
+		.name = "jhb100-sys0-pll",
+		.driver_data = (unsigned long)&jhb100_sys0_pll,
+	},
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(platform, jhb100_pll_ids);
+
 static struct platform_driver jhb100_pll_driver = {
 	.probe = jhb100_pll_probe,
+	.id_table = jhb100_pll_ids,
 	.driver = {
 		.name = "clk-starfive-jhb100-pll",
 		.of_match_table = jhb100_pll_match,
 		.suppress_bind_attrs = true,
 	},
 };

==============================================================

> >
> > >
> > > >
> > > > > 	},
> > > > > };
> > > > >
> > > > > static const struct mfd_cell jhb100_per0_subdev[] = {
> > > > > 	{
> > > > > 		.name = "jhb100-per0-pll",
> > > >
> > > > Why do these other ones need to be modified?
> > >
> > > I was thinking, since sys0-pll has been adjusted, would it be better
> > > to also
> > adjust per0-pll and per1-pll together in a unified way?
> >
> > I wouldn't complicate them with things that they don't need, so it
> > depends on if these other syscon regions contain more than just PLLs
> > and if there'll ever be drivers for the other stuff in those regions.
> >
> > >
> > > >
> > > > > 	},
> > > > > };
> > > > >
> > > > > static const struct mfd_cell jhb100_per1_subdev[] = {
> > > > > 	{
> > > > > 		.name = "jhb100-per1-pll",
> > > > > 	},
> > > > > };
> > > > >
> > > > > static const struct mfd_cell jhb100_ pcierp _subdev[] = {
> > > > > 	{
> > > > > 		.name = "jhb100-pcierp-reset",
> > > > > 	},
> > > > > };
> > >

Best Regards,
Changhuang