net: ixp4xx_hss: Check features using syscon

If we access the syscon (expansion bus config registers) using the
syscon regmap instead of relying on direct accessor functions,
we do not need to call this static code in the machine
(arch/arm/mach-ixp4xx/common.c) which makes things less dependent
on custom machine-dependent code.

Look up the syscon regmap and handle the error: this will make
deferred probe work with relation to the syscon.

Select the syscon in Kconfig and depend on OF so we know that
all we need will be available.

Cc: David S. Miller <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20220211223238.648934-10-linus.walleij@linaro.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/net/wan/Kconfig

@@ -293,7 +293,8 @@ config SLIC_DS26522
 config IXP4XX_HSS
 	tristate "Intel IXP4xx HSS (synchronous serial port) support"
 	depends on HDLC && IXP4XX_NPE && IXP4XX_QMGR
-	depends on ARCH_IXP4XX
+	depends on ARCH_IXP4XX && OF
+	select MFD_SYSCON
 	help
 	  Say Y here if you want to use built-in HSS ports
 	  on IXP4xx processor.

drivers/net/wan/ixp4xx_hss.c

@@ -16,8 +16,10 @@
 #include <linux/hdlc.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
+#include <linux/mfd/syscon.h>
 #include <linux/platform_device.h>
 #include <linux/poll.h>
+#include <linux/regmap.h>
 #include <linux/slab.h>
 #include <linux/gpio/consumer.h>
 #include <linux/of.h>
@@ -1389,9 +1391,28 @@ static int ixp4xx_hss_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct net_device *ndev;
 	struct device_node *np;
+	struct regmap *rmap;
 	struct port *port;
 	hdlc_device *hdlc;
 	int err;
+	u32 val;
+
+	/*
+	 * Go into the syscon and check if we have the HSS and HDLC
+	 * features available, else this will not work.
+	 */
+	rmap = syscon_regmap_lookup_by_compatible("syscon");
+	if (IS_ERR(rmap))
+		return dev_err_probe(dev, PTR_ERR(rmap),
+				     "failed to look up syscon\n");
+
+	val = cpu_ixp4xx_features(rmap);
+
+	if ((val & (IXP4XX_FEATURE_HDLC | IXP4XX_FEATURE_HSS)) !=
+	    (IXP4XX_FEATURE_HDLC | IXP4XX_FEATURE_HSS)) {
+		dev_err(dev, "HDLC and HSS feature unavailable in platform\n");
+		return -ENODEV;
+	}
 
 	np = dev->of_node;
 
@@ -1516,25 +1537,9 @@ static struct platform_driver ixp4xx_hss_driver = {
 	.probe		= ixp4xx_hss_probe,
 	.remove		= ixp4xx_hss_remove,
 };
-
-static int __init hss_init_module(void)
-{
-	if ((ixp4xx_read_feature_bits() &
-	     (IXP4XX_FEATURE_HDLC | IXP4XX_FEATURE_HSS)) !=
-	    (IXP4XX_FEATURE_HDLC | IXP4XX_FEATURE_HSS))
-		return -ENODEV;
-
-	return platform_driver_register(&ixp4xx_hss_driver);
-}
-
-static void __exit hss_cleanup_module(void)
-{
-	platform_driver_unregister(&ixp4xx_hss_driver);
-}
+module_platform_driver(ixp4xx_hss_driver);
 
 MODULE_AUTHOR("Krzysztof Halasa");
 MODULE_DESCRIPTION("Intel IXP4xx HSS driver");
 MODULE_LICENSE("GPL v2");
 MODULE_ALIAS("platform:ixp4xx_hss");
-module_init(hss_init_module);
-module_exit(hss_cleanup_module);