target/linux/generic/pending-3.18/092-03-spi-Only-idle-the-message-pump-in-the-worker-kthread.patch

   1 From: Mark Brown <broonie@kernel.org>
   2 Date: Wed, 10 Dec 2014 13:46:33 +0000
   3 Subject: [PATCH] spi: Only idle the message pump in the worker kthread
   4
   5 In order to avoid the situation where the kthread is waiting for another
   6 context to make the hardware idle let the message pump know if it's being
   7 called from the worker thread context and if it isn't then defer to the
   8 worker thread instead of idling the hardware immediately. This will ensure
   9 that if this situation happens we block rather than busy waiting.
  10
  11 Signed-off-by: Mark Brown <broonie@kernel.org>
  12 ---
  13
  14 --- a/drivers/spi/spi.c
  15 +++ b/drivers/spi/spi.c
  16 @@ -875,8 +875,9 @@ void spi_finalize_current_transfer(struc
  17  EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);
  18
  19  /**
  20 - * spi_pump_messages - kthread work function which processes spi message queue
  21 - * @work: pointer to kthread work struct contained in the master struct
  22 + * __spi_pump_messages - function which processes spi message queue
  23 + * @master: master to process queue for
  24 + * @in_kthread: true if we are in the context of the message pump thread
  25   *
  26   * This function checks if there is any spi message in the queue that
  27   * needs processing and if so call out to the driver to initialize hardware
  28 @@ -886,10 +887,8 @@ EXPORT_SYMBOL_GPL(spi_finalize_current_t
  29   * inside spi_sync(); the queue extraction handling at the top of the
  30   * function should deal with this safely.
  31   */
  32 -static void spi_pump_messages(struct kthread_work *work)
  33 +static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
  34  {
  35 -       struct spi_master *master =
  36 -               container_of(work, struct spi_master, pump_messages);
  37         unsigned long flags;
  38         bool was_busy = false;
  39         int ret;
  40 @@ -916,6 +915,15 @@ static void spi_pump_messages(struct kth
  41                         spin_unlock_irqrestore(&master->queue_lock, flags);
  42                         return;
  43                 }
  44 +
  45 +               /* Only do teardown in the thread */
  46 +               if (!in_kthread) {
  47 +                       queue_kthread_work(&master->kworker,
  48 +                                          &master->pump_messages);
  49 +                       spin_unlock_irqrestore(&master->queue_lock, flags);
  50 +                       return;
  51 +               }
  52 +
  53                 master->busy = false;
  54                 master->idling = true;
  55                 spin_unlock_irqrestore(&master->queue_lock, flags);
  56 @@ -1004,6 +1012,18 @@ static void spi_pump_messages(struct kth
  57         }
  58  }
  59
  60 +/**
  61 + * spi_pump_messages - kthread work function which processes spi message queue
  62 + * @work: pointer to kthread work struct contained in the master struct
  63 + */
  64 +static void spi_pump_messages(struct kthread_work *work)
  65 +{
  66 +       struct spi_master *master =
  67 +               container_of(work, struct spi_master, pump_messages);
  68 +
  69 +       __spi_pump_messages(master, true);
  70 +}
  71 +
  72  static int spi_init_queue(struct spi_master *master)
  73  {
  74         struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
  75 @@ -2165,7 +2185,7 @@ static int __spi_sync(struct spi_device
  76                  * can.
  77                  */
  78                 if (master->transfer == spi_queued_transfer)
  79 -                       spi_pump_messages(&master->pump_messages);
  80 +                       __spi_pump_messages(master, false);
  81
  82                 wait_for_completion(&done);
  83                 status = message->status;