[U-Boot] Driver Model and DTS Parsing

[Jon Loeliger]

Folks,

I'd like to discuss the new Driver Model's parsing of the DTS file
for the purposes of instancing and binding devices as I was not
able to get the existing code to work anything like I was expecting.

The current code only finds and binds the top-level nodes of the
DTS file.  This leads to a bind function one-level above where it
should be for each of the actual device nodes and an extra "parent"
node that is empty.  For example, the gpio_exynos_gpio_bind()
function here:

http://git.denx.de/?p=u-boot/u-boot-x86.git;a=blob;f=drivers/gpio/s5p_gpio.c;h=8100d50ed2da686353c593ed90693c441cf24b4f;hb=refs/heads/us-gpioc

Looks like this:

386 /**
387  * We have a top-level GPIO device with no actual GPIOs. It has a child
388  * device for each Exynos GPIO bank.
389  */
390 static int gpio_exynos_bind(struct device *parent)
391 {
392         struct exynos_gpio_platdata *plat = parent->platdata;
393         struct s5p_gpio_bank *bank;
394         const void *blob = gd->fdt_blob;
395         int node;
396
397         /* If this is a child device, there is nothing to do here */
398         if (plat)
399                 return 0;
400
401         bank = (struct s5p_gpio_bank *)fdtdec_get_addr(gd->fdt_blob,
402
parent->of_offset, "reg");
403         for (node = fdt_first_subnode(blob, parent->of_offset); node > 0;
404              node = fdt_next_subnode(blob, node)) {
405                 struct exynos_gpio_platdata *plat;
406                 struct device *dev;
407                 int ret;
408
409                 plat = calloc(1, sizeof(*plat));
410                 if (!plat)
411                         return -ENOMEM;
412                 plat->bank = bank;
413                 plat->port_name = fdt_get_name(blob, node, NULL);
414
415                 ret = device_bind(parent, parent->driver,
416                                         plat->port_name, plat, -1, &dev);
417                 if (ret)
418                         return ret;
419                 dev->of_offset = parent->of_offset;
420                 bank++;
421         }
422
423         return 0;
424 }

Why is this function being called once at the parent node, which
then iterates over each device, instantiates and binds it?  Why
isn't this function instead called once for each individual device
as matched from the DTS?  Where did the compatible matching
and check take place in this implementation?


Instead, I think it should be a recursive structure essentially
identical in structure to the Linux of_platform_populate() function.
There should be a compatible matching step, and then the
call to bind the specific instance.

Am I missing something here?  Or is this code that just needs to
be developed further still?

Thanks,
jdl