185 lines
6.1 KiB
Diff
185 lines
6.1 KiB
Diff
From: Mark Brown <broonie@kernel.org>
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Date: Tue, 9 Dec 2014 21:38:05 +0000
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Subject: [PATCH] spi: Pump transfers inside calling context for spi_sync()
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If we are using the standard SPI message pump (which all drivers should be
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transitioning over to) then special case the message enqueue and instead of
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starting the worker thread to push messages to the hardware do so in the
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context of the caller if the controller is idle. This avoids a context
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switch in the common case where the controller has a single user in a
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single thread, for short PIO transfers there may be no need to context
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switch away from the calling context to complete the transfer.
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The code is a bit more complex than is desirable in part due to the need
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to handle drivers not using the standard queue and in part due to handling
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the various combinations of bus locking and asynchronous submission in
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interrupt context.
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It is still suboptimal since it will still wake the message pump for each
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transfer in order to schedule idling of the hardware and if multiple
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contexts are using the controller simultaneously a caller may end up
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pumping a message for some random other thread rather than for itself,
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and if the thread ends up deferring due to another context idling the
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hardware then it will just busy wait. It can, however, have the benefit
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of aggregating power up and down of the hardware when a caller performs
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a series of transfers back to back without any need for the use of
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spi_async().
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Signed-off-by: Mark Brown <broonie@kernel.org>
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---
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--- a/drivers/spi/spi.c
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+++ b/drivers/spi/spi.c
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@@ -882,6 +882,9 @@ EXPORT_SYMBOL_GPL(spi_finalize_current_t
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* needs processing and if so call out to the driver to initialize hardware
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* and transfer each message.
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*
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+ * Note that it is called both from the kthread itself and also from
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+ * inside spi_sync(); the queue extraction handling at the top of the
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+ * function should deal with this safely.
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*/
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static void spi_pump_messages(struct kthread_work *work)
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{
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@@ -900,6 +903,13 @@ static void spi_pump_messages(struct kth
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return;
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}
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+ /* If another context is idling the device then defer */
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+ if (master->idling) {
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+ queue_kthread_work(&master->kworker, &master->pump_messages);
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+ spin_unlock_irqrestore(&master->queue_lock, flags);
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+ return;
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+ }
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+
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/* Check if the queue is idle */
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if (list_empty(&master->queue) || !master->running) {
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if (!master->busy) {
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@@ -907,7 +917,9 @@ static void spi_pump_messages(struct kth
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return;
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}
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master->busy = false;
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+ master->idling = true;
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spin_unlock_irqrestore(&master->queue_lock, flags);
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+
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kfree(master->dummy_rx);
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master->dummy_rx = NULL;
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kfree(master->dummy_tx);
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@@ -921,6 +933,10 @@ static void spi_pump_messages(struct kth
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pm_runtime_put_autosuspend(master->dev.parent);
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}
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trace_spi_master_idle(master);
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+
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+ spin_lock_irqsave(&master->queue_lock, flags);
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+ master->idling = false;
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+ spin_unlock_irqrestore(&master->queue_lock, flags);
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return;
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}
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@@ -1166,12 +1182,9 @@ static int spi_destroy_queue(struct spi_
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return 0;
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}
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-/**
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- * spi_queued_transfer - transfer function for queued transfers
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- * @spi: spi device which is requesting transfer
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- * @msg: spi message which is to handled is queued to driver queue
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- */
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-static int spi_queued_transfer(struct spi_device *spi, struct spi_message *msg)
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+static int __spi_queued_transfer(struct spi_device *spi,
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+ struct spi_message *msg,
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+ bool need_pump)
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{
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struct spi_master *master = spi->master;
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unsigned long flags;
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@@ -1186,13 +1199,23 @@ static int spi_queued_transfer(struct sp
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msg->status = -EINPROGRESS;
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list_add_tail(&msg->queue, &master->queue);
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- if (!master->busy)
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+ if (!master->busy && need_pump)
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queue_kthread_work(&master->kworker, &master->pump_messages);
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spin_unlock_irqrestore(&master->queue_lock, flags);
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return 0;
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}
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+/**
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+ * spi_queued_transfer - transfer function for queued transfers
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+ * @spi: spi device which is requesting transfer
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+ * @msg: spi message which is to handled is queued to driver queue
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+ */
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+static int spi_queued_transfer(struct spi_device *spi, struct spi_message *msg)
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+{
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+ return __spi_queued_transfer(spi, msg, true);
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+}
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+
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static int spi_master_initialize_queue(struct spi_master *master)
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{
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int ret;
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@@ -2104,19 +2127,46 @@ static int __spi_sync(struct spi_device
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DECLARE_COMPLETION_ONSTACK(done);
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int status;
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struct spi_master *master = spi->master;
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+ unsigned long flags;
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+
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+ status = __spi_validate(spi, message);
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+ if (status != 0)
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+ return status;
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message->complete = spi_complete;
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message->context = &done;
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+ message->spi = spi;
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if (!bus_locked)
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mutex_lock(&master->bus_lock_mutex);
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- status = spi_async_locked(spi, message);
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+ /* If we're not using the legacy transfer method then we will
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+ * try to transfer in the calling context so special case.
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+ * This code would be less tricky if we could remove the
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+ * support for driver implemented message queues.
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+ */
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+ if (master->transfer == spi_queued_transfer) {
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+ spin_lock_irqsave(&master->bus_lock_spinlock, flags);
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+
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+ trace_spi_message_submit(message);
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+
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+ status = __spi_queued_transfer(spi, message, false);
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+
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+ spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);
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+ } else {
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+ status = spi_async_locked(spi, message);
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+ }
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if (!bus_locked)
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mutex_unlock(&master->bus_lock_mutex);
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if (status == 0) {
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+ /* Push out the messages in the calling context if we
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+ * can.
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+ */
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+ if (master->transfer == spi_queued_transfer)
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+ spi_pump_messages(&master->pump_messages);
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+
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wait_for_completion(&done);
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status = message->status;
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}
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--- a/include/linux/spi/spi.h
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+++ b/include/linux/spi/spi.h
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@@ -260,6 +260,7 @@ static inline void spi_unregister_driver
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* @pump_messages: work struct for scheduling work to the message pump
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* @queue_lock: spinlock to syncronise access to message queue
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* @queue: message queue
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+ * @idling: the device is entering idle state
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* @cur_msg: the currently in-flight message
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* @cur_msg_prepared: spi_prepare_message was called for the currently
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* in-flight message
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@@ -425,6 +426,7 @@ struct spi_master {
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spinlock_t queue_lock;
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struct list_head queue;
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struct spi_message *cur_msg;
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+ bool idling;
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bool busy;
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bool running;
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bool rt;
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