[PATCH v16 mfd 1/8] mfd: ocelot: add helper to get regmap from a resource

[Colin Foster <colin.foster@xxxxxxxxxxxxxxxx>]

Several ocelot-related modules are designed for MMIO / regmaps. As such,
they often use a combination of devm_platform_get_and_ioremap_resource()
and devm_regmap_init_mmio().

Operating in an MFD might be different, in that it could be memory mapped,
or it could be SPI, I2C... In these cases a fallback to use IORESOURCE_REG
instead of IORESOURCE_MEM becomes necessary.

When this happens, there's redundant logic that needs to be implemented in
every driver. In order to avoid this redundancy, utilize a single function
that, if the MFD scenario is enabled, will perform this fallback logic.

Signed-off-by: Colin Foster <colin.foster@xxxxxxxxxxxxxxxx>
Reviewed-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
---
v16
    * Add Andy Reviewed-by tag

v15
    * Add missed errno.h and ioport.h includes
    * Add () to function references in both the commit log and comments

v14
    * Add header guard
    * Change regs type from u32* to void*
    * Add Reviewed-by tag

---
 MAINTAINERS                |  5 +++
 include/linux/mfd/ocelot.h | 62 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)
 create mode 100644 include/linux/mfd/ocelot.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 8a5012ba6ff9..e0732e9f9090 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14741,6 +14741,11 @@ F:	net/dsa/tag_ocelot.c
 F:	net/dsa/tag_ocelot_8021q.c
 F:	tools/testing/selftests/drivers/net/ocelot/*
 
+OCELOT EXTERNAL SWITCH CONTROL
+M:	Colin Foster <colin.foster@xxxxxxxxxxxxxxxx>
+S:	Supported
+F:	include/linux/mfd/ocelot.h
+
 OCXL (Open Coherent Accelerator Processor Interface OpenCAPI) DRIVER
 M:	Frederic Barrat <fbarrat@xxxxxxxxxxxxx>
 M:	Andrew Donnellan <ajd@xxxxxxxxxxxxx>
diff --git a/include/linux/mfd/ocelot.h b/include/linux/mfd/ocelot.h
new file mode 100644
index 000000000000..dd72073d2d4f
--- /dev/null
+++ b/include/linux/mfd/ocelot.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+/* Copyright 2022 Innovative Advantage Inc. */
+
+#ifndef _LINUX_MFD_OCELOT_H
+#define _LINUX_MFD_OCELOT_H
+
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/ioport.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/types.h>
+
+struct resource;
+
+static inline struct regmap *
+ocelot_regmap_from_resource_optional(struct platform_device *pdev,
+				     unsigned int index,
+				     const struct regmap_config *config)
+{
+	struct device *dev = &pdev->dev;
+	struct resource *res;
+	void __iomem *regs;
+
+	/*
+	 * Don't use _get_and_ioremap_resource() here, since that will invoke
+	 * prints of "invalid resource" which will simply add confusion.
+	 */
+	res = platform_get_resource(pdev, IORESOURCE_MEM, index);
+	if (res) {
+		regs = devm_ioremap_resource(dev, res);
+		if (IS_ERR(regs))
+			return ERR_CAST(regs);
+		return devm_regmap_init_mmio(dev, regs, config);
+	}
+
+	/*
+	 * Fall back to using REG and getting the resource from the parent
+	 * device, which is possible in an MFD configuration
+	 */
+	if (dev->parent) {
+		res = platform_get_resource(pdev, IORESOURCE_REG, index);
+		if (!res)
+			return NULL;
+
+		return dev_get_regmap(dev->parent, res->name);
+	}
+
+	return NULL;
+}
+
+static inline struct regmap *
+ocelot_regmap_from_resource(struct platform_device *pdev, unsigned int index,
+			    const struct regmap_config *config)
+{
+	struct regmap *map;
+
+	map = ocelot_regmap_from_resource_optional(pdev, index, config);
+	return map ?: ERR_PTR(-ENOENT);
+}
+
+#endif
-- 
2.25.1