irqchip/qcom-mpm: Support passing a slice of SRAM as reg space

The MPM hardware is accessible from the ARM CPUs through a shared memory
region (RPM MSG RAM) which is also concurrently accessed by other kinds of
cores on the system like modem, ADSP etc.

Modeling this relation in a (somewhat) sane manner in the device tree
requires to

  - either present the MPM as a child of said memory region, which
    makes little sense, as a mapped memory carveout is not a bus.

  - define nodes which bleed their register spaces into one another

  - or passing their slice of the MSG RAM through a property

Go with the third option and add a way to map a region passed through the
"qcom,rpm-msg-ram" property as register space for the MPM interrupt
controller.

The current way of using 'reg' is preserved for backwards compatibility
reasons.

[ tglx: Massaged changelog ]
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Link: https://lore.kernel.org/r/20230328-topic-msgram_mpm-v7-2-6ee2bfeaac2c@linaro.org

drivers/irqchip/irq-qcom-mpm.c

@@ -14,6 +14,7 @@
 #include <linux/mailbox_client.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/of_address.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
 #include <linux/pm_domain.h>
@@ -322,8 +323,10 @@ static int qcom_mpm_init(struct device_node *np, struct device_node *parent)
 	struct device *dev = &pdev->dev;
 	struct irq_domain *parent_domain;
 	struct generic_pm_domain *genpd;
+	struct device_node *msgram_np;
 	struct qcom_mpm_priv *priv;
 	unsigned int pin_cnt;
+	struct resource res;
 	int i, irq;
 	int ret;
 
@@ -374,9 +377,26 @@ static int qcom_mpm_init(struct device_node *np, struct device_node *parent)
 
 	raw_spin_lock_init(&priv->lock);
 
-	priv->base = devm_platform_ioremap_resource(pdev, 0);
-	if (IS_ERR(priv->base))
-		return PTR_ERR(priv->base);
+	/* If we have a handle to an RPM message ram partition, use it. */
+	msgram_np = of_parse_phandle(np, "qcom,rpm-msg-ram", 0);
+	if (msgram_np) {
+		ret = of_address_to_resource(msgram_np, 0, &res);
+		if (ret) {
+			of_node_put(msgram_np);
+			return ret;
+		}
+
+		/* Don't use devm_ioremap_resource, as we're accessing a shared region. */
+		priv->base = devm_ioremap(dev, res.start, resource_size(&res));
+		of_node_put(msgram_np);
+		if (IS_ERR(priv->base))
+			return PTR_ERR(priv->base);
+	} else {
+		/* Otherwise, fall back to simple MMIO. */
+		priv->base = devm_platform_ioremap_resource(pdev, 0);
+		if (IS_ERR(priv->base))
+			return PTR_ERR(priv->base);
+	}
 
 	for (i = 0; i < priv->reg_stride; i++) {
 		qcom_mpm_write(priv, MPM_REG_ENABLE, i, 0);