[v4,2/3] spi: Allow SPI devices to request the pumping thread be realtime
diff mbox series

Message ID 20190515164814.258898-3-dianders@chromium.org
State New
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Series
  • spi: A better solution for cros_ec_spi reliability
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Commit Message

Doug Anderson May 15, 2019, 4:48 p.m. UTC
Right now the only way to get the SPI pumping thread bumped up to
realtime priority is for the controller to request it.  However it may
be that the controller works fine with the normal priority but
communication to a particular SPI device on the bus needs realtime
priority.

Let's add a way for devices to request realtime priority when they set
themselves up.

NOTE: this will just affect the priority of transfers that end up on
the SPI core's pumping thread.  In many cases transfers happen in the
context of the caller so if you need realtime priority for all
transfers you should ensure the calling context is also realtime
priority.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
---

Changes in v4: None
Changes in v3:
- SPI core change now like patch v1 patch #2 (with name "rt").

Changes in v2:
- Now only force transfers to the thread for devices that want it.
- Squashed patch #1 and #2 together.
- Renamed variable to "force_rt_transfers".

 drivers/spi/spi.c       | 36 ++++++++++++++++++++++++++++++------
 include/linux/spi/spi.h |  2 ++
 2 files changed, 32 insertions(+), 6 deletions(-)

Comments

Enric Balletbo i Serra May 21, 2019, 7:49 a.m. UTC | #1
Hi,

On 15/5/19 18:48, Douglas Anderson wrote:
> Right now the only way to get the SPI pumping thread bumped up to
> realtime priority is for the controller to request it.  However it may
> be that the controller works fine with the normal priority but
> communication to a particular SPI device on the bus needs realtime
> priority.
> 
> Let's add a way for devices to request realtime priority when they set
> themselves up.
> 
> NOTE: this will just affect the priority of transfers that end up on
> the SPI core's pumping thread.  In many cases transfers happen in the
> context of the caller so if you need realtime priority for all
> transfers you should ensure the calling context is also realtime
> priority.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Guenter Roeck <groeck@chromium.org>

Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

Thanks,
 Enric

> ---
> 
> Changes in v4: None
> Changes in v3:
> - SPI core change now like patch v1 patch #2 (with name "rt").
> 
> Changes in v2:
> - Now only force transfers to the thread for devices that want it.
> - Squashed patch #1 and #2 together.
> - Renamed variable to "force_rt_transfers".
> 
>  drivers/spi/spi.c       | 36 ++++++++++++++++++++++++++++++------
>  include/linux/spi/spi.h |  2 ++
>  2 files changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 8eb7460dd744..466984796dd9 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -1364,10 +1364,32 @@ static void spi_pump_messages(struct kthread_work *work)
>  	__spi_pump_messages(ctlr, true);
>  }
>  
> -static int spi_init_queue(struct spi_controller *ctlr)
> +/**
> + * spi_set_thread_rt - set the controller to pump at realtime priority
> + * @ctlr: controller to boost priority of
> + *
> + * This can be called because the controller requested realtime priority
> + * (by setting the ->rt value before calling spi_register_controller()) or
> + * because a device on the bus said that its transfers needed realtime
> + * priority.
> + *
> + * NOTE: at the moment if any device on a bus says it needs realtime then
> + * the thread will be at realtime priority for all transfers on that
> + * controller.  If this eventually becomes a problem we may see if we can
> + * find a way to boost the priority only temporarily during relevant
> + * transfers.
> + */
> +static void spi_set_thread_rt(struct spi_controller *ctlr)
>  {
>  	struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
>  
> +	dev_info(&ctlr->dev,
> +		"will run message pump with realtime priority\n");
> +	sched_setscheduler(ctlr->kworker_task, SCHED_FIFO, &param);
> +}
> +
> +static int spi_init_queue(struct spi_controller *ctlr)
> +{
>  	ctlr->running = false;
>  	ctlr->busy = false;
>  
> @@ -1387,11 +1409,8 @@ static int spi_init_queue(struct spi_controller *ctlr)
>  	 * request and the scheduling of the message pump thread. Without this
>  	 * setting the message pump thread will remain at default priority.
>  	 */
> -	if (ctlr->rt) {
> -		dev_info(&ctlr->dev,
> -			"will run message pump with realtime priority\n");
> -		sched_setscheduler(ctlr->kworker_task, SCHED_FIFO, &param);
> -	}
> +	if (ctlr->rt)
> +		spi_set_thread_rt(ctlr);
>  
>  	return 0;
>  }
> @@ -2982,6 +3001,11 @@ int spi_setup(struct spi_device *spi)
>  
>  	spi_set_cs(spi, false);
>  
> +	if (spi->rt && !spi->controller->rt) {
> +		spi->controller->rt = true;
> +		spi_set_thread_rt(spi->controller);
> +	}
> +
>  	dev_dbg(&spi->dev, "setup mode %d, %s%s%s%s%u bits/w, %u Hz max --> %d\n",
>  			(int) (spi->mode & (SPI_CPOL | SPI_CPHA)),
>  			(spi->mode & SPI_CS_HIGH) ? "cs_high, " : "",
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index 053abd22ad31..15505c2485d6 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -109,6 +109,7 @@ void spi_statistics_add_transfer_stats(struct spi_statistics *stats,
>   *	This may be changed by the device's driver, or left at the
>   *	default (0) indicating protocol words are eight bit bytes.
>   *	The spi_transfer.bits_per_word can override this for each transfer.
> + * @rt: Make the pump thread real time priority.
>   * @irq: Negative, or the number passed to request_irq() to receive
>   *	interrupts from this device.
>   * @controller_state: Controller's runtime state
> @@ -143,6 +144,7 @@ struct spi_device {
>  	u32			max_speed_hz;
>  	u8			chip_select;
>  	u8			bits_per_word;
> +	bool			rt;
>  	u32			mode;
>  #define	SPI_CPHA	0x01			/* clock phase */
>  #define	SPI_CPOL	0x02			/* clock polarity */
>
Mark Brown May 23, 2019, 1:46 p.m. UTC | #2
On Wed, May 15, 2019 at 09:48:12AM -0700, Douglas Anderson wrote:
> Right now the only way to get the SPI pumping thread bumped up to
> realtime priority is for the controller to request it.  However it may
> be that the controller works fine with the normal priority but
> communication to a particular SPI device on the bus needs realtime
> priority.

The following changes since commit a188339ca5a396acc588e5851ed7e19f66b0ebd9:

  Linux 5.2-rc1 (2019-05-19 15:47:09 -0700)

are available in the Git repository at:

  https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git tags/spi-rt-pump

for you to fetch changes up to 924b5867e7bd6a6a98014f0517b747465b108011:

  spi: Allow SPI devices to request the pumping thread be realtime (2019-05-23 14:44:02 +0100)

----------------------------------------------------------------
spi: Allow setting pump to RT priority

----------------------------------------------------------------
Douglas Anderson (1):
      spi: Allow SPI devices to request the pumping thread be realtime

 drivers/spi/spi.c       | 36 ++++++++++++++++++++++++++++++------
 include/linux/spi/spi.h |  2 ++
 2 files changed, 32 insertions(+), 6 deletions(-)

Patch
diff mbox series

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 8eb7460dd744..466984796dd9 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1364,10 +1364,32 @@  static void spi_pump_messages(struct kthread_work *work)
 	__spi_pump_messages(ctlr, true);
 }
 
-static int spi_init_queue(struct spi_controller *ctlr)
+/**
+ * spi_set_thread_rt - set the controller to pump at realtime priority
+ * @ctlr: controller to boost priority of
+ *
+ * This can be called because the controller requested realtime priority
+ * (by setting the ->rt value before calling spi_register_controller()) or
+ * because a device on the bus said that its transfers needed realtime
+ * priority.
+ *
+ * NOTE: at the moment if any device on a bus says it needs realtime then
+ * the thread will be at realtime priority for all transfers on that
+ * controller.  If this eventually becomes a problem we may see if we can
+ * find a way to boost the priority only temporarily during relevant
+ * transfers.
+ */
+static void spi_set_thread_rt(struct spi_controller *ctlr)
 {
 	struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
 
+	dev_info(&ctlr->dev,
+		"will run message pump with realtime priority\n");
+	sched_setscheduler(ctlr->kworker_task, SCHED_FIFO, &param);
+}
+
+static int spi_init_queue(struct spi_controller *ctlr)
+{
 	ctlr->running = false;
 	ctlr->busy = false;
 
@@ -1387,11 +1409,8 @@  static int spi_init_queue(struct spi_controller *ctlr)
 	 * request and the scheduling of the message pump thread. Without this
 	 * setting the message pump thread will remain at default priority.
 	 */
-	if (ctlr->rt) {
-		dev_info(&ctlr->dev,
-			"will run message pump with realtime priority\n");
-		sched_setscheduler(ctlr->kworker_task, SCHED_FIFO, &param);
-	}
+	if (ctlr->rt)
+		spi_set_thread_rt(ctlr);
 
 	return 0;
 }
@@ -2982,6 +3001,11 @@  int spi_setup(struct spi_device *spi)
 
 	spi_set_cs(spi, false);
 
+	if (spi->rt && !spi->controller->rt) {
+		spi->controller->rt = true;
+		spi_set_thread_rt(spi->controller);
+	}
+
 	dev_dbg(&spi->dev, "setup mode %d, %s%s%s%s%u bits/w, %u Hz max --> %d\n",
 			(int) (spi->mode & (SPI_CPOL | SPI_CPHA)),
 			(spi->mode & SPI_CS_HIGH) ? "cs_high, " : "",
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 053abd22ad31..15505c2485d6 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -109,6 +109,7 @@  void spi_statistics_add_transfer_stats(struct spi_statistics *stats,
  *	This may be changed by the device's driver, or left at the
  *	default (0) indicating protocol words are eight bit bytes.
  *	The spi_transfer.bits_per_word can override this for each transfer.
+ * @rt: Make the pump thread real time priority.
  * @irq: Negative, or the number passed to request_irq() to receive
  *	interrupts from this device.
  * @controller_state: Controller's runtime state
@@ -143,6 +144,7 @@  struct spi_device {
 	u32			max_speed_hz;
 	u8			chip_select;
 	u8			bits_per_word;
+	bool			rt;
 	u32			mode;
 #define	SPI_CPHA	0x01			/* clock phase */
 #define	SPI_CPOL	0x02			/* clock polarity */