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SubjectRe: [PATCH v4 2/3] spi: Allow SPI devices to request the pumping thread be realtime
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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 */
>

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