On 1/25/2012 2:44 AM, Linus WALLEIJ wrote:
> From: Chris Blair <chris.bl...@stericsson.com>
>
> This switches the PL022 worker to a kthread in order to get
> hold of a mechanism to control the message pump priority. On
> low-latency systems elevating the message kthread to realtime
> priority give a real sleek response curve. This has been
> confirmed by measurements. Realtime priority elevation for
> a certain PL022 port can be requested from platform data.
>
> Signed-off-by: Chris Blair <chris.bl...@stericsson.com>
> Signed-off-by: Linus Walleij <linus.wall...@linaro.org>
> ---
> drivers/spi/spi-pl022.c | 77 +++++++++++++++++++++++++++++--------------
> include/linux/amba/pl022.h | 3 ++
> 2 files changed, 55 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/spi/spi-pl022.c b/drivers/spi/spi-pl022.c
> index 2f9cb43..81847c9 100644
> --- a/drivers/spi/spi-pl022.c
> +++ b/drivers/spi/spi-pl022.c
> @@ -29,7 +29,7 @@
> #include <linux/errno.h>
> #include <linux/interrupt.h>
> #include <linux/spi/spi.h>
> -#include <linux/workqueue.h>
> +#include <linux/kthread.h>
> #include <linux/delay.h>
> #include <linux/clk.h>
> #include <linux/err.h>
> @@ -41,6 +41,7 @@
> #include <linux/dma-mapping.h>
> #include <linux/scatterlist.h>
> #include <linux/pm_runtime.h>
> +#include <linux/sched.h>
>
> /*
> * This macro is used to define some register default values.
> @@ -330,12 +331,13 @@ struct vendor_data {
> * @clk: outgoing clock "SPICLK" for the SPI bus
> * @master: SPI framework hookup
> * @master_info: controller-specific data from machine setup
> - * @workqueue: a workqueue on which any spi_message request is queued
> - * @pump_messages: work struct for scheduling work to the workqueue
> + * @kworker: thread struct for message pump
> + * @kworker_task: pointer to task for message pump kworker thread
> + * @pump_messages: work struct for scheduling work to the message pump
> * @queue_lock: spinlock to syncronise access to message queue
> * @queue: message queue
> - * @busy: workqueue is busy
> - * @running: workqueue is running
> + * @busy: message pump is busy
> + * @running: message pump is running
> * @pump_transfers: Tasklet used in Interrupt Transfer mode
> * @cur_msg: Pointer to current spi_message being processed
> * @cur_transfer: Pointer to current spi_transfer
> @@ -365,9 +367,10 @@ struct pl022 {
> struct clk *clk;
> struct spi_master *master;
> struct pl022_ssp_controller *master_info;
> - /* Driver message queue */
> - struct workqueue_struct *workqueue;
> - struct work_struct pump_messages;
> + /* Driver message pump */
> + struct kthread_worker kworker;
> + struct task_struct *kworker_task;
> + struct kthread_work pump_messages;
> spinlock_t queue_lock;
> struct list_head queue;
> bool busy;
> @@ -504,7 +507,7 @@ static void giveback(struct pl022 *pl022)
> pl022->cur_msg = NULL;
> pl022->cur_transfer = NULL;
> pl022->cur_chip = NULL;
> - queue_work(pl022->workqueue, &pl022->pump_messages);
> + queue_kthread_work(&pl022->kworker, &pl022->pump_messages);
> spin_unlock_irqrestore(&pl022->queue_lock, flags);
>
> msg->state = NULL;
> @@ -1494,8 +1497,8 @@ out:
> }
>
> /**
> - * pump_messages - Workqueue function which processes spi message queue
> - * @data: pointer to private data of SSP driver
> + * pump_messages - kthread work function which processes spi message queue
> + * @work: pointer to kthread work struct contained in the pl022 private
> struct
> *
> * This function checks if there is any spi message in the queue that
> * needs processing and delegate control to appropriate function
> @@ -1503,7 +1506,7 @@ out:
> * based on the kind of the transfer
> *
> */
> -static void pump_messages(struct work_struct *work)
> +static void pump_messages(struct kthread_work *work)
> {
> struct pl022 *pl022 =
> container_of(work, struct pl022, pump_messages);
> @@ -1556,7 +1559,7 @@ static void pump_messages(struct work_struct *work)
> if (!was_busy)
> /*
> * We enable the core voltage and clocks here, then the clocks
> - * and core will be disabled when this workqueue is run again
> + * and core will be disabled when this thread is run again
> * and there is no more work to be done.
> */
> pm_runtime_get_sync(&pl022->adev->dev);
> @@ -1572,6 +1575,8 @@ static void pump_messages(struct work_struct *work)
>
> static int __init init_queue(struct pl022 *pl022)
> {
> + struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
> +
> INIT_LIST_HEAD(&pl022->queue);
> spin_lock_init(&pl022->queue_lock);
>
> @@ -1581,11 +1586,29 @@ static int __init init_queue(struct pl022 *pl022)
> tasklet_init(&pl022->pump_transfers, pump_transfers,
> (unsigned long)pl022);
>
> - INIT_WORK(&pl022->pump_messages, pump_messages);
> - pl022->workqueue = create_singlethread_workqueue(
> + init_kthread_worker(&pl022->kworker);
> + pl022->kworker_task = kthread_run(kthread_worker_fn,
> + &pl022->kworker,
> dev_name(pl022->master->dev.parent));
> - if (pl022->workqueue == NULL)
> - return -EBUSY;
> + if (IS_ERR(pl022->kworker_task)) {
> + dev_err(&pl022->adev->dev,
> + "failed to create message pump task\n");
> + return -ENOMEM;
> + }
> + init_kthread_work(&pl022->pump_messages, pump_messages);
> +
> + /*
> + * Board config will indicate if this controller should run the
> + * message pump with high (realtime) priority to reduce the transfer
> + * latency on the bus by minimising the delay between a transfer
> + * request and the scheduling of the message pump thread. Without this
> + * setting the message pump thread will remain at default priority.
> + */
> + if (pl022->master_info->rt) {
> + dev_info(&pl022->adev->dev,
> + "will run message pump with realtime priority\n");
> + sched_setscheduler(pl022->kworker_task, SCHED_FIFO, ¶m);
> + }
>
> return 0;
> }
> @@ -1608,7 +1631,7 @@ static int start_queue(struct pl022 *pl022)
> pl022->next_msg_cs_active = false;
> spin_unlock_irqrestore(&pl022->queue_lock, flags);
>
> - queue_work(pl022->workqueue, &pl022->pump_messages);
> + queue_kthread_work(&pl022->kworker, &pl022->pump_messages);
>
> return 0;
> }
> @@ -1646,16 +1669,20 @@ static int destroy_queue(struct pl022 *pl022)
> int status;
>
> status = stop_queue(pl022);
> - /* we are unloading the module or failing to load (only two calls
> +
> + /*
> + * We are unloading the module or failing to load (only two calls
> * to this routine), and neither call can handle a return value.
> - * However, destroy_workqueue calls flush_workqueue, and that will
> - * block until all work is done. If the reason that stop_queue
> - * timed out is that the work will never finish, then it does no
> - * good to call destroy_workqueue, so return anyway. */
> + * However, flush_kthread_worker will block until all work is done.
> + * If the reason that stop_queue timed out is that the work will never
> + * finish, then it does no good to call flush/stop thread, so
> + * return anyway.
> + */
> if (status != 0)
> return status;
>
> - destroy_workqueue(pl022->workqueue);
> + flush_kthread_worker(&pl022->kworker);
> + kthread_stop(pl022->kworker_task);
>
> return 0;
> }
> @@ -1802,7 +1829,7 @@ static int pl022_transfer(struct spi_device *spi,
> struct spi_message *msg)
>
> list_add_tail(&msg->queue, &pl022->queue);
> if (pl022->running && !pl022->busy)
> - queue_work(pl022->workqueue, &pl022->pump_messages);
> + queue_kthread_work(&pl022->kworker, &pl022->pump_messages);
>
> spin_unlock_irqrestore(&pl022->queue_lock, flags);
> return 0;
> diff --git a/include/linux/amba/pl022.h b/include/linux/amba/pl022.h
> index 572f637..3672f40 100644
> --- a/include/linux/amba/pl022.h
> +++ b/include/linux/amba/pl022.h
> @@ -241,6 +241,8 @@ struct dma_chan;
> * @autosuspend_delay: delay in ms following transfer completion before the
> * runtime power management system suspends the device. A setting of 0
> * indicates no delay and the device will be suspended immediately.
> + * @rt: indicates the controller should run the message pump with realtime
> + * priority to minimise the transfer latency on the bus.
> */
> struct pl022_ssp_controller {
> u16 bus_id;
> @@ -250,6 +252,7 @@ struct pl022_ssp_controller {
> void *dma_rx_param;
> void *dma_tx_param;
> int autosuspend_delay;
> + bool rt;
> };
>
> /**
Looks fine.
Acked-by: Viresh Kumar <viresh.ku...@st.com>
--
viresh
------------------------------------------------------------------------------
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