[i2c] amba_device resource

[Drasko Draskovic]

Hi all,
I have question about resource member of amba_device struct. Struct
platform_device looks like this:
/* drivers/base/platform.c */

struct platform_device {
    char        * name;
    u32        id;
    struct device    dev;
    u32        num_resources;
    struct resource    * resource;
};

and amba_device:

struct amba_device {
    struct device        dev;
    struct resource        res;
    u64            dma_mask;
    unsigned int        periphid;
    unsigned int        irq[AMBA_NR_IRQS];
};

So, amba_device has only one resource member while platform_device holds
array of resources.
In linux/drivers/i2c/busses/i2c-s3c2410.c, platform_device is used, and it
looks like this:

/* s3c24xx_i2c_probe
 *
 * called by the bus driver when a suitable device is found
*/

static int s3c24xx_i2c_probe(struct device *dev)
{
    struct platform_device *pdev = to_platform_device(dev);
    struct s3c24xx_i2c *i2c = &s3c24xx_i2c;
    struct resource *res;
    int ret;
...
...

/* map the registers */

    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (res == NULL) {
        dev_err(dev, "cannot find IO resource\n");
        ret = -ENOENT;
        goto out;
    }

    i2c->ioarea = request_mem_region(res->start, (res->end-res->start)+1,
                     pdev->name);

    if (i2c->ioarea == NULL) {
        dev_err(dev, "cannot request IO\n");
        ret = -ENXIO;
        goto out;
    }

    i2c->regs = ioremap(res->start, (res->end-res->start)+1);

    if (i2c->regs == NULL) {
        dev_err(dev, "cannot map IO\n");
        ret = -ENXIO;
        goto out;
    }

    dev_dbg(dev, "registers %p (%p, %p)\n", i2c->regs, i2c->ioarea, res);

...
...

/* find the IRQ for this unit (note, this relies on the init call to
     * ensure no current IRQs pending
     */

    res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
    if (res == NULL) {
        dev_err(dev, "cannot find IRQ\n");
        ret = -ENOENT;
        goto out;
    }

    ret = request_irq(res->start, s3c24xx_i2c_irq, SA_INTERRUPT,
              pdev->name, i2c);

    if (ret != 0) {
        dev_err(dev, "cannot claim IRQ\n");
        goto out;
    }

    i2c->irq = res;

    dev_dbg(dev, "irq resource %p (%ld)\n", res, res->start);

However, I want my i2c adapter to be an amba_device, so I am wondering how
to change calls like this:
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
and how will it impact code...

Why platform_device holds array of resources, while amba_device holds one
resource? Can anybody explain a bit this resource(s) and what this member
should represent and describe?

Also -- why this function static int s3c24xx_i2c_probe(struct device *dev) gets
device* dev as an argument and not platform_device, so then has to cast: struct
platform_device *pdev = to_platform_device(dev); ?Is this correct way to
write these kinds of functions and why (since I noted that some of the
functions are taking directly platform_device as a parameter)? How to cast
to _amba_device (if needed)?


Best regards,

-- 
Drasko DRASKOVIC

Software Developer
Elsys-DESIGN
Belgrade, Serbia
Tel. +381.11.311.5252
Fax. +381.11.311.5251
www.elsys-design.com
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