[U-Boot] [Question of dm serial] Is pending handler optional?

[Masahiro YAMADA]

Hi Simon,

I have questions of driver model serial.


The comment block in include/serial.h states .pending is optional

---------------------------->8-------------------------------
* pending() - Check if input/output characters are waiting
*
* This can be used to return an indication of the number of waiting
* characters if the driver knows this (e.g. by looking at the FIFO
* level). It is acceptable to return 1 if an indeterminant number
* of characters is waiting.
*
* This method is optional.
----------------------------8<-------------------------------


When I was testing my driver model conversion patch,
I noticed ctrlc() function would not work without .pending handler.



The function ctrlc() calls tstc()
and if it returns non-zero value, it also calls getc().



If .pending handler is not implemented,
tstc() function always return 1,
even if no input character is available in UART FIFO;
As a result, getc() function will get stuck in

do {
        err = ops->getc(cur_dev);
} while (err == -EAGAIN);

loop.


For example, "help" command does not work.


So, .pending is mandatory, isn't it?



One more question.

The comment says .pending is:
Check if input/output characters are waiting


Should .pending check output buffer? or input only?




-- 
Best Regards
Masahiro Yamada