On 02/13/2013 06:16 PM, Kuninori Morimoto wrote:
Hi Stephen
Thank you for your explain. I think I could understand, but not 100%.
Well, any driver that could be used with it will need to implement the .of_xlate() callback. The simple-audio code would still be 100% independent from any CPU or CODEC, since of_xlate would be a standard interface/API that any CPU or CODEC driver could implement, and any ASoC machine driver could call.
(snip)
Yes, .of_xlate() wouldn't have to be implemented by the WM8903 CODEC driver for the tegra-wm8903 machine driver to use the WM8903 CODEC. However, if it /was/ implemented, it wouldn't stop tegra-wm8903 from working. And later, it may help unify all the simple Tegra machine drivers into one, since they could also become CODEC-independent, and hence become unified (or at least mostly unified) code.
I guess, this .of_xlate should has "public" interface for all drivers, not simple-card special.
Yes exactly. And this means that it always returns a particular type of object, not something different depending on who calls it; this is relevant to the discussion below.
Now, simple-card needs "dai name" from struct of_phandle_args.
Yes.
This .of_xlate can be used from other driver if there is such kind of driver. Now, as example, I assumed this "other driver" needs something other data pointer from .of_xlate here.
Well, .of_xlate is /defined/ as taking the of_phandle_args and returning the DAI name that the of_phandle_args represents. If there's ever a need to translate some of_phandle_args to something else, that should be a different function.
To that end, perhaps calling the function .of_xlate_dai_name might be more future-proof; if we ever needed to translate say a CODEC widget name, we could add a separate .of_xlate_widget_name function to do that later, with zero effect on the .of_xlate_dai_name function.
Then can .of_xlate has *void pointer for return ?
I think it would always return a string; the function parameter would be "char **dai_name".
In my check, the parameter of .of_xlate in gpio_chip and pmw has "driver specific" parameter.
It shouldn't. A GPIO driver's .of_xlate should /always/ take an of_phandle_args, and translate it to a Linux (or perhaps chip-relative) GPIO number, plus Linux GPIO flags. There should be nothing driver-specific about the data it returns. The format of the device tree cells that represent that data can be driver- (really, DT binding-) specific; the whole point of the .of_xlate function is to translate that binding-specific format into some standard internal Linux format.
My pseudo code now is below. But is this correct ??
simple-card OF has <&device port> : of_phandle_args will be used as "port" spec other driver OF has <xxxx yyy zzz> : of_phandle_args will be used as "something" spec
-- asoc -- struct snd_soc_dai_driver { ... int (*of_xlate)(struct snd_soc_dai_driver *driver, const struct of_phandle_args *spec, // driver specific spec void *data); // for return data
As I mentioned above, that last parameter should be "char **dai_name", and the function name probably of_xlate_dai_name.
...}
-- MULTI .of_xlate support codec driver ---
#ifdef CONFIG_ASOC_SIMPLE_AUDIO_OF
No need to the ifdef; just provide a single definition which does one thing.
int codec_of_xlate(struct snd_soc_dai_driver *driver, const struct of_phandle_args *portspec, void *data); { /* * for simple-card which needs "dai name" * * of_phandle_args is used as "port" spec */ *data = port_to_dai_name(portspec);
Yes, that's about right. Given how simple the implementation of port_to_dai_name() is, I would simply write the code directly in the implementation of of_xlate(). I assume you were writing pseudo-code simply to avoid spelling out the implementation though.
return 0;} #elif CONFIG_OTHER_DIRVER_IT_NEEDS_xxx_POINTER_OF int codec_of_xlate(struct snd_soc_dai_driver *driver, const struct of_phandle_args *something_spec, void *data); { /* * for "other" driver which needs something pointer * * of_phandle_args is used as "something" spec */ *data = something_necessary_pointer(something_spec); return 0; } #else #define codec_of_xlate() NULL #endif
struct snd_soc_dai_driver codec_driver = { ... .of_xlate = codec_of_xlate, ... }