[PATCH] hvc_console: fix dropping of characters when output byte channel is full
scottwood at freescale.com
Wed Sep 15 05:22:36 EST 2010
On Tue, 14 Sep 2010 12:17:21 -0700
Andrew Morton <akpm at linux-foundation.org> wrote:
> On Fri, 20 Aug 2010 13:45:21 -0500
> Timur Tabi <timur at freescale.com> wrote:
> > hvc_console_print() calls the HVC client driver's put_chars() callback
> > to write some characters to the console. If the callback returns 0, that
> > indicates that no characters were written (perhaps the output buffer is
> > full), but hvc_console_print() treats that as an error and discards the
> > rest of the buffer.
> > So change hvc_console_print() to just loop and call put_chars() again if it
> > returns a 0 return code.
> Seems rather dangerous. The upper layer will sit there chewing 100%
> CPU for as long as the lower layer is congested.
This is just for printk(), not user output. This is exactly what
printk() has always done for real serial ports.
> > This change makes hvc_console_print() behave more like hvc_push(), which
> > does check for a 0 return code and re-schedules itself.
> Yes, hvc_push() reschedules.
hvc_push() is not relevant to kernel console output.
hvc_console_write() currently does not reschedule anything. It just
drops characters when busy.
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