Re: [PATCH 2/4] arch/arm/mach-at91/clock.c: Add missing IS_ERR test

Russell King - ARM Linux
2011-01-24T23:24:15Z

On Tue, Jan 25, 2011 at 10:51:38AM +1300, Ryan Mallon wrote:
> You could, but it would not be helpful. Clock associations are used so
> that _different_ devices can have the same function and map to the
> correct clock. This is used when there are multiple instances of a
> single peripheral. For example, the uart clocks work like this:
>
> at91_clock_associate("usart1_clk", &pdev->dev, "usart");
>
> so then you can do this in a driver:
>
> uart_clk = clk_get(&pdev->dev, "usart");
>
> Rather than:
>
> uart_clk = clk_get(NULL, "usart1_clk");
>
> The former will find the correct uart clock for the device. Because each
> uart is a separate device the correct clock will be selected for each uart.
>
> My point was that there should be no overlap between clk->name and
> clk->function otherwise clk_get will not be able to return the correct
> clock.

It would be nice if AT91 could switch over to using clkdev at some
point, which greatly helps with associating struct clk's with their
device/function names - and reduces the amount of "different" code.

You can then use clk_add_alias() to create aliases of an existing
clock.

Looking at your clk_get(), I think one way to do this would be, in
clk_register():

struct clk_lookup *cl;

/* create function-only entry */
cl = clkdev_alloc(clk, clk->name, NULL);
if (!cl)
return -ENOMEM;
clkdev_add(cl);

/* not sure if you need this? */
if (clk->dev && clk->function) {
cl = clkdev_alloc(clk, clk->function, "%s", dev_name(clk->dev));
if (!cl)
return -ENOMEM;
clkdev_add(cl);
}

at91_clock_associate() becomes:

err = clk_add_alias(func, dev_name(dev), id, NULL);
return err;

Although maybe in the long run see about removing at91_clock_associate()
entirely as its just a wrapper.

The only requirement there is that 'dev' in each case is a registered
device, otherwise dev_name() won't work.

You can then use the generic clk_get()/clk_put() which clkdev provides.