[U-Boot] dm: device_id info

[Simon Glass]

Hi Jagan,

On 9 January 2015 at 03:53, Jagan Teki <jagannadh.teki at gmail.com> wrote:
> Hi,
>
> I'm exploring internals of dm where I'm just comparing udevice with Linux
> model especially on device_id scenarios.
>
> udevice_id - u-boot
>
> Linux:
> --------
> platform_device_id
> of_device_id
>
> spi_device_id
> input_device_id
> ..............
> .......
> pci_device_id
>
> 1. Does this udevice_id is a generic model in u-boot for all variant of devices?
>     Bcz Linux defines each devices have own device_id entries.

The device id is intended to describe a particular node compatible
string which can be used with a driver. It corresponds most closely
with of_device_id.

On the platform data size (not device tree) we have struct driver_info
which is intended to connect a driver with its platform data, to
produce a device.

> 2. diff of of_device_id vs udevice_id

Linux has:

struct of_device_id
{
char name[32];
char type[32];
char compatible[128];
const void *data;
};

U-Boot doesn't have a name and type. It uses a pointer instead of 128
bytes for the compatible string (for efficiency). For U-Boot we use a
ulong instead of a pointer for data.

> 3. udevice_id vs fdt function calls, suppose If I write a dm driver
> where my board doesn't
>     have fdt support, is this a valid scenario.

I'm not sure what you are asking. I'd encourage you to use device tree
for new drivers.

> 4. Pls- add any info which I haven't covered.

There's quite a bit of info about platform data and device tree in the
driver model README.txt.

Regards,
Simon