How to read address of reserved memory in device tree

Question

I'm writing a device driver in Linux for a small device. The device has some particular memory constraints that forces me to carve out a piece of memory, and in my driver I need to know the address (and the size) of the reserved memory

/ {
    reserved-memory {
        my_reserve: my_reserve@a0000000 {
            compatible = "shared-dma-pool";
            reg = <0 0xa0000000 0 0x20000>;
            no-map;
        };
    };

    my_device {
        compatible = "my_device";
        memory-region = <&my_reserve>;
    };
};

How do I read the physical address of the reserved memory (i.e. how do I read the value 0xa000'0000) in my device driver? There seem to be a API for reserved memory, but nothing that I can see that returns a struct reserved_mem *

Answer 1

If struct device *hwdev points to your hardware struct device (for example, if hwdev points to the dev member of a struct platform_device), then this snippet illustrates how to access the device tree node of the reserved memory region and convert that to a struct resource.

        struct device_node *memnp;
        struct resource mem_res;
        int rc;

        /* Get pointer to memory region device node from "memory-region" phandle. */
        memnp = of_parse_phandle(hwdev->of_node, "memory-region", 0);
        if (!memnp) {
                dev_err(hwdev, "no memory-region node\n");
                rc = -ENXIO;
                goto err1;
        }
        /* Convert memory region to a struct resource */
        rc = of_address_to_resource(memnp, 0, &mem_res);
        /* finished with memnp */
        of_node_put(memnp);
        if (rc) {
                dev_err(hwdev, "failed to translate memory-region to a resource\n");
                goto err1;
        }

The start address ends up in mem_res.start and the length is given by resource_size(&mem_res);.