[U-Boot] putc

[Martin Dorwig]

Am Mittwoch, 12. November 2014, 19:32:21 schrieben Sie:
> Hi Martin,
> 
> On 30 October 2014 00:45, Martin Dorwig <dorwig at tetronik.com> wrote:
> > Am Mittwoch, 29. Oktober 2014, 13:03:41 schrieben Sie:
> >> Hi Martin,
> >> 
> >> On 28 October 2014 07:23, Martin Dorwig <dorwig at tetronik.com> wrote:
> >> > Hello,
> >> > after updating u-boot from git v2014.10
> >> > i just noticed that my standalone  application outputs garbage using
> >> > putc.
> >> > after some investigation i found that the gd->jt[XF_putc] is assigned a
> >> > dev->putc pointer in "common/console.c function console_setfile"
> >> > 
> >> > the dev->putc is declared in include/stdio_dev.h as
> >> > void (*putc)(struct stdio_dev *dev, const char c);
> >> > 
> >> > int include/exports.h this function is declared as
> >> > void putc(const char);
> >> > 
> >> > this was introduced with commit id
> >> > 709ea543b92489e7729d2d7ddd6c9f451e52158c
> >> 
> >> That's unfortunate. Is the stdio device pointer available in the
> >> standalone application?
> >> 
> >> Perhaps gd->jt should point to a structure of strongly-typed
> >> functions? Then we would get a build error in this case.
> >> 
> >> Regards,
> >> Simon
> > 
> > What is the motivation to override the jumptable slots ?
> > Why can't they be untouched like this
> > gd->jt[XF_getc] = getc;
> > gd->jt[XF_tstc] = tstc;
> > gd->jt[XF_putc] = putc;
> > gd->jt[XF_puts] = puts;
> > redirection of the console to another device is honored in the
> > implementation of the functions themselves.
> > for example the putc function:
> > it calls pre_console_putc before a console is present
> > if GD_FLG_DEVINIT is set, it calls fputc(stdout,c) which calls
> > console_putc(stdout,c) which in turn calls stdio_devices[stdout]-
> > 
> >>putc(stdio_devices[file], c);
> >>
> > else it calls serial_putc(c)
> 
> I have taken a bit of a look at this.
> 
> I have not actually touched the jumptable slots. The one you mention
> was assigned to dev->putc() before and after. The problem is that now
> dev->putc() has two parameters, the first being 'dev'.
> 
> dev->putc() is the device's putc function - typically the serial port
> or a display.
> 
> The putc() function you mention is the console out, that outputs to
> all stdout devices.
> 
> So yes we could change the bahaviour so that it calls putc(). I think
> this will work, and it probably isn't going to result in a change in
> behaviour for many boards since they only have a single stdout.
> 
> Alternatively we could require the stdio device parameter to be passed
> in. I'm not sure that will work though - how will the external program
> get at it?
> 
> In any case, teh void *gd->jt[] is not serving our purpose here - it
> should be changed to proper function pointer types so that the
> compiler can check that this sort of thing doesn't happen.
> 
> Please let me know what you think should be done here.
> 
> Regards,
> Simon

The jumptable is initialized once, and i don't see any reason to overwrite it.
Adding a parameter to these exported functions will break backward 
compatibility
of existing standalone apps
Regards,
Martin