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    Subject[PATCH] [15/50] hvc_console: Improve tty/console put_chars handling
    Date
    2.6.35-longterm review patch.  If anyone has any objections, please let me know.

    ------------------
    From: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>

    [ upstream commit 8c2381af0d3ef62a681dac5a141b6dabb27bf2e1 ]

    Currently, the hvc_console_print() function drops console output if the
    hvc backend's put_chars() returns 0. This patch changes this behavior
    to allow a retry through returning -EAGAIN.

    This change also affects the hvc_push() function. Both functions are
    changed to handle -EAGAIN and to retry the put_chars() operation.

    If a hvc backend returns -EAGAIN, the retry handling differs:

    - hvc_console_print() spins to write the complete console output.
    - hvc_push() behaves the same way as for returning 0.

    Now hvc backends can indirectly control the way how console output is
    handled through the hvc console layer.

    Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
    Acked-by: Anton Blanchard <anton@samba.org>
    Cc: <stable@kernel.org>
    Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Signed-off-by: Andi Kleen <ak@linux.intel.com>

    Index: linux-2.6.35.y/drivers/char/hvc_console.c
    ===================================================================
    --- linux-2.6.35.y.orig/drivers/char/hvc_console.c
    +++ linux-2.6.35.y/drivers/char/hvc_console.c
    @@ -163,8 +163,10 @@ static void hvc_console_print(struct con
    } else {
    r = cons_ops[index]->put_chars(vtermnos[index], c, i);
    if (r <= 0) {
    - /* throw away chars on error */
    - i = 0;
    + /* throw away characters on error
    + * but spin in case of -EAGAIN */
    + if (r != -EAGAIN)
    + i = 0;
    } else if (r > 0) {
    i -= r;
    if (i > 0)
    @@ -448,7 +450,7 @@ static int hvc_push(struct hvc_struct *h

    n = hp->ops->put_chars(hp->vtermno, hp->outbuf, hp->n_outbuf);
    if (n <= 0) {
    - if (n == 0) {
    + if (n == 0 || n == -EAGAIN) {
    hp->do_wakeup = 1;
    return 0;
    }

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