[PATCH] hvc_console: fix dropping of characters when output byte channel is full

[Timur Tabi]

Andrew,

Would you please take a moment to review this patch I sent last month?
I'd like for it to be incorporated into 2.6.37, but I'm having a hard
time finding someone to consider it.

Thanks.

On Fri, Aug 20, 2010 at 1:45 PM, 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.
>
> This change makes hvc_console_print() behave more like hvc_push(), which
> does check for a 0 return code and re-schedules itself.
>
> Signed-off-by: Timur Tabi <timur at freescale.com>
> ---
>  drivers/char/hvc_console.c |   19 ++++++++++++++++++-
>  1 files changed, 18 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
> index fa27d16..b4deffd 100644
> --- a/drivers/char/hvc_console.c
> +++ b/drivers/char/hvc_console.c
> @@ -3,6 +3,7 @@
>  * Copyright (C) 2001 Paul Mackerras <paulus at au.ibm.com>, IBM
>  * Copyright (C) 2004 Benjamin Herrenschmidt <benh at kernel.crashing.org>, IBM Corp.
>  * Copyright (C) 2004 IBM Corporation
> + * Copyright 2009 Freescale Semiconductor, Inc.
>  *
>  * Additional Author(s):
>  *  Ryan S. Arnold <rsa at us.ibm.com>
> @@ -141,6 +142,7 @@ static void hvc_console_print(struct console *co, const char *b,
>        char c[N_OUTBUF] __ALIGNED__;
>        unsigned i = 0, n = 0;
>        int r, donecr = 0, index = co->index;
> +       unsigned int timeout = 1000000; /* Keep trying for up to one second */
>
>        /* Console access attempt outside of acceptable console range. */
>        if (index >= MAX_NR_HVC_CONSOLES)
> @@ -152,6 +154,10 @@ static void hvc_console_print(struct console *co, const char *b,
>
>        while (count > 0 || i > 0) {
>                if (count > 0 && i < sizeof(c)) {
> +                       /* If the local buffer (c) is not full, then copy some
> +                        * bytes from the input buffer to it. We stop when the
> +                        * local buffer is full. \n is converted to \r\n.
> +                        */
>                        if (b[n] == '\n' && !donecr) {
>                                c[i++] = '\r';
>                                donecr = 1;
> @@ -162,14 +168,25 @@ static void hvc_console_print(struct console *co, const char *b,
>                        }
>                } else {
>                        r = cons_ops[index]->put_chars(vtermnos[index], c, i);
> -                       if (r <= 0) {
> +                       if (r < 0) {
>                                /* throw away chars on error */
>                                i = 0;
>                        } else if (r > 0) {
>                                i -= r;
>                                if (i > 0)
>                                        memmove(c, c+r, i);
> +                       } else {
> +                               /* If r == 0, then the client driver didn't do
> +                                * anything, so wait 1us and try again.  If we
> +                                * time out, then just exit.
> +                                */
> +                               if (!--timeout)
> +                                       return;
> +                               udelay(1);
> +                               continue;
>                        }
> +                       /* Reset the timeout */
> +                       timeout = 1000000;
>                }
>        }
>  }
> --
> 1.7.0.1
>
>
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-- 
Timur Tabi
Linux kernel developer at Freescale