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platform/chrome: cros_ec_spi: Move to real time priority for transfers
In commit37a186225a
("platform/chrome: cros_ec_spi: Transfer messages at high priority") we moved transfers to a high priority workqueue. This helped make them much more reliable. ...but, we still saw failures. We were actually finding ourselves competing for time with dm-crypt which also scheduled work on HIGHPRI workqueues. While we can consider reverting the change that made dm-crypt run its work at HIGHPRI, the argument in commita1b89132dc
("dm crypt: use WQ_HIGHPRI for the IO and crypt workqueues") is somewhat compelling. It does make sense for IO to be scheduled at a priority that's higher than the default user priority. It also turns out that dm-crypt isn't alone in using high priority like this. loop_prepare_queue() does something similar for loopback devices. Looking in more detail, it can be seen that the high priority workqueue isn't actually that high of a priority. It runs at MIN_NICE which is _fairly_ high priority but still below all real time priority. Should we move cros_ec_spi to real time priority to fix our problems, or is this just escalating a priority war? I'll argue here that cros_ec_spi _does_ belong at real time priority. Specifically cros_ec_spi actually needs to run quickly for correctness. As I understand this is exactly what real time priority is for. There currently doesn't appear to be any way to use the standard workqueue APIs with a real time priority, so we'll switch over to using using a kthread worker. We'll match the priority that the SPI core uses when it wants to do things on a realtime thread and just use "MAX_RT_PRIO - 1". This commit plus the patch ("platform/chrome: cros_ec_spi: Request the SPI thread be realtime") are enough to get communications very close to 100% reliable (the only known problem left is when serial console is turned on, which isn't something that happens in shipping devices). Specifically this test case now passes (tested on rk3288-veyron-jerry): dd if=/dev/zero of=/var/log/foo.txt bs=4M count=512& while true; do ectool version > /dev/null; done It should be noted that "/var/log" is encrypted (and goes through dm-crypt) and also passes through a loopback device. Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Guenter Roeck <groeck@chromium.org> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
This commit is contained in:
parent
26a14267af
commit
7dadf88f8d
1 changed files with 53 additions and 12 deletions
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@ -12,7 +12,7 @@
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#include <linux/platform_device.h>
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#include <linux/slab.h>
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#include <linux/spi/spi.h>
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#include <uapi/linux/sched/types.h>
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/* The header byte, which follows the preamble */
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#define EC_MSG_HEADER 0xec
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@ -67,12 +67,14 @@
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* is sent when we want to turn on CS at the start of a transaction.
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* @end_of_msg_delay: used to set the delay_usecs on the spi_transfer that
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* is sent when we want to turn off CS at the end of a transaction.
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* @high_pri_worker: Used to schedule high priority work.
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*/
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struct cros_ec_spi {
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struct spi_device *spi;
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s64 last_transfer_ns;
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unsigned int start_of_msg_delay;
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unsigned int end_of_msg_delay;
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struct kthread_worker *high_pri_worker;
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};
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typedef int (*cros_ec_xfer_fn_t) (struct cros_ec_device *ec_dev,
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@ -89,7 +91,7 @@ typedef int (*cros_ec_xfer_fn_t) (struct cros_ec_device *ec_dev,
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*/
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struct cros_ec_xfer_work_params {
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struct work_struct work;
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struct kthread_work work;
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cros_ec_xfer_fn_t fn;
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struct cros_ec_device *ec_dev;
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struct cros_ec_command *ec_msg;
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@ -632,7 +634,7 @@ static int do_cros_ec_cmd_xfer_spi(struct cros_ec_device *ec_dev,
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return ret;
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}
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static void cros_ec_xfer_high_pri_work(struct work_struct *work)
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static void cros_ec_xfer_high_pri_work(struct kthread_work *work)
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{
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struct cros_ec_xfer_work_params *params;
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@ -644,12 +646,14 @@ static int cros_ec_xfer_high_pri(struct cros_ec_device *ec_dev,
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struct cros_ec_command *ec_msg,
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cros_ec_xfer_fn_t fn)
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{
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struct cros_ec_xfer_work_params params;
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INIT_WORK_ONSTACK(¶ms.work, cros_ec_xfer_high_pri_work);
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params.ec_dev = ec_dev;
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params.ec_msg = ec_msg;
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params.fn = fn;
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struct cros_ec_spi *ec_spi = ec_dev->priv;
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struct cros_ec_xfer_work_params params = {
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.work = KTHREAD_WORK_INIT(params.work,
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cros_ec_xfer_high_pri_work),
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.ec_dev = ec_dev,
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.ec_msg = ec_msg,
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.fn = fn,
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};
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/*
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* This looks a bit ridiculous. Why do the work on a
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@ -660,9 +664,8 @@ static int cros_ec_xfer_high_pri(struct cros_ec_device *ec_dev,
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* context switched out for too long and the EC giving up on
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* the transfer.
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*/
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queue_work(system_highpri_wq, ¶ms.work);
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flush_work(¶ms.work);
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destroy_work_on_stack(¶ms.work);
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kthread_queue_work(ec_spi->high_pri_worker, ¶ms.work);
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kthread_flush_work(¶ms.work);
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return params.ret;
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}
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@ -694,6 +697,40 @@ static void cros_ec_spi_dt_probe(struct cros_ec_spi *ec_spi, struct device *dev)
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ec_spi->end_of_msg_delay = val;
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}
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static void cros_ec_spi_high_pri_release(void *worker)
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{
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kthread_destroy_worker(worker);
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}
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static int cros_ec_spi_devm_high_pri_alloc(struct device *dev,
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struct cros_ec_spi *ec_spi)
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{
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struct sched_param sched_priority = {
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.sched_priority = MAX_RT_PRIO - 1,
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};
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int err;
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ec_spi->high_pri_worker =
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kthread_create_worker(0, "cros_ec_spi_high_pri");
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if (IS_ERR(ec_spi->high_pri_worker)) {
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err = PTR_ERR(ec_spi->high_pri_worker);
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dev_err(dev, "Can't create cros_ec high pri worker: %d\n", err);
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return err;
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}
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err = devm_add_action_or_reset(dev, cros_ec_spi_high_pri_release,
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ec_spi->high_pri_worker);
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if (err)
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return err;
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err = sched_setscheduler_nocheck(ec_spi->high_pri_worker->task,
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SCHED_FIFO, &sched_priority);
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if (err)
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dev_err(dev, "Can't set cros_ec high pri priority: %d\n", err);
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return err;
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}
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static int cros_ec_spi_probe(struct spi_device *spi)
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{
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struct device *dev = &spi->dev;
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@ -732,6 +769,10 @@ static int cros_ec_spi_probe(struct spi_device *spi)
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ec_spi->last_transfer_ns = ktime_get_ns();
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err = cros_ec_spi_devm_high_pri_alloc(dev, ec_spi);
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if (err)
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return err;
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err = cros_ec_register(ec_dev);
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if (err) {
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dev_err(dev, "cannot register EC\n");
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