[PATCH] soc: qcom: rpmh-rsc: Sleep waiting for tcs slots to be free

Stephen Boyd
2020-07-23T01:01:40Z

The busy loop in rpmh_rsc_send_data() is written with the assumption
that the udelay will be preempted by the tcs_tx_done() irq handler when
the TCS slots are all full. This doesn't hold true when the calling
thread is an irqthread and the tcs_tx_done() irq is also an irqthread.
That's because kernel irqthreads are SCHED_FIFO and thus need to
voluntarily give up priority by calling into the scheduler so that other
threads can run.

I see RCU stalls when I boot with irqthreads on the kernel commandline
because the modem remoteproc driver is trying to send an rpmh async
message from an irqthread that needs to give up the CPU for the rpmh
irqthread to run and clear out tcs slots.

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 0-....: (1 GPs behind) idle=402/1/0x4000000000000002 softirq=2108/2109 fqs=4920
(t=21016 jiffies g=2933 q=590)
Task dump for CPU 0:
irq/11-smp2p R running task 0 148 2 0x00000028
Call trace:
dump_backtrace+0x0/0x154
show_stack+0x20/0x2c
sched_show_task+0xfc/0x108
dump_cpu_task+0x44/0x50
rcu_dump_cpu_stacks+0xa4/0xf8
rcu_sched_clock_irq+0x7dc/0xaa8
update_process_times+0x30/0x54
tick_sched_handle+0x50/0x64
tick_sched_timer+0x4c/0x8c
__hrtimer_run_queues+0x21c/0x36c
hrtimer_interrupt+0xf0/0x22c
arch_timer_handler_phys+0x40/0x50
handle_percpu_devid_irq+0x114/0x25c
__handle_domain_irq+0x84/0xc4
gic_handle_irq+0xd0/0x178
el1_irq+0xbc/0x180
save_return_addr+0x18/0x28
return_address+0x54/0x88
preempt_count_sub+0x40/0x88
_raw_spin_unlock_irqrestore+0x4c/0x6c
___ratelimit+0xd0/0x128
rpmh_rsc_send_data+0x24c/0x378
__rpmh_write+0x1b0/0x208
rpmh_write_async+0x90/0xbc
rpmhpd_send_corner+0x60/0x8c
rpmhpd_aggregate_corner+0x8c/0x124
rpmhpd_set_performance_state+0x8c/0xbc
_genpd_set_performance_state+0xdc/0x1b8
dev_pm_genpd_set_performance_state+0xb8/0xf8
q6v5_pds_disable+0x34/0x60 [qcom_q6v5_mss]
qcom_msa_handover+0x38/0x44 [qcom_q6v5_mss]
q6v5_handover_interrupt+0x24/0x3c [qcom_q6v5]
handle_nested_irq+0xd0/0x138
qcom_smp2p_intr+0x188/0x200
irq_thread_fn+0x2c/0x70
irq_thread+0xfc/0x14c
kthread+0x11c/0x12c
ret_from_fork+0x10/0x18

This busy loop naturally lends itself to using a wait queue so that each
thread that tries to send a message will sleep waiting on the waitqueue
and only be woken up when a free slot is available. This should make
things more predictable too because the scheduler will be able to sleep
tasks that are waiting on a free tcs instead of the busy loop we
currently have today.

Cc: Douglas Anderson <dianders@chromium.org>
Cc: Maulik Shah <mkshah@codeaurora.org>
Cc: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
drivers/soc/qcom/rpmh-internal.h | 2 +
drivers/soc/qcom/rpmh-rsc.c | 101 ++++++++++++-------------------
2 files changed, 41 insertions(+), 62 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h
index ef60e790a750..9a325bac58fe 100644
--- a/drivers/soc/qcom/rpmh-internal.h
+++ b/drivers/soc/qcom/rpmh-internal.h
@@ -8,6 +8,7 @@
#define __RPM_INTERNAL_H__

#include <linux/bitmap.h>
+#include <linux/wait.h>
#include <soc/qcom/tcs.h>

#define TCS_TYPE_NR 4
@@ -118,6 +119,7 @@ struct rsc_drv {
struct tcs_group tcs[TCS_TYPE_NR];
DECLARE_BITMAP(tcs_in_use, MAX_TCS_NR);
spinlock_t lock;
+ wait_queue_head_t tcs_wait;
struct rpmh_ctrlr client;
};

diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index 076fd27f3081..6c758b052c95 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -19,6 +19,7 @@
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
+#include <linux/wait.h>

#include <soc/qcom/cmd-db.h>
#include <soc/qcom/tcs.h>
@@ -444,6 +445,7 @@ static irqreturn_t tcs_tx_done(int irq, void *p)
*/
if (!drv->tcs[ACTIVE_TCS].num_tcs)
enable_tcs_irq(drv, i, false);
+ wake_up(&drv->tcs_wait);
spin_unlock(&drv->lock);
if (req)
rpmh_tx_done(req, err);
@@ -562,44 +564,59 @@ static int find_free_tcs(struct tcs_group *tcs)
return -EBUSY;
}

+static int claim_tcs_for_req(struct rsc_drv *drv, struct tcs_group *tcs,
+ const struct tcs_request *msg)
+{
+ int ret;
+
+ /*
+ * The h/w does not like if we send a request to the same address,
+ * when one is already in-flight or being processed.
+ */
+ ret = check_for_req_inflight(drv, tcs, msg);
+ if (ret)
+ return ret;
+
+ return find_free_tcs(tcs);
+}
+
/**
- * tcs_write() - Store messages into a TCS right now, or return -EBUSY.
+ * rpmh_rsc_send_data() - Write / trigger active-only message.
* @drv: The controller.
* @msg: The data to be sent.
*
- * Grabs a TCS for ACTIVE_ONLY transfers and writes the messages to it.
- *
- * If there are no free TCSes for ACTIVE_ONLY transfers or if a command for
- * the same address is already transferring returns -EBUSY which means the
- * client should retry shortly.
+ * NOTES:
+ * - This is only used for "ACTIVE_ONLY" since the limitations of this
+ * function don't make sense for sleep/wake cases.
+ * - To do the transfer, we will grab a whole TCS for ourselves--we don't
+ * try to share. If there are none available we'll wait indefinitely
+ * for a free one.
+ * - This function will not wait for the commands to be finished, only for
+ * data to be programmed into the RPMh. See rpmh_tx_done() which will
+ * be called when the transfer is fully complete.
+ * - This function must be called with interrupts enabled. If the hardware
+ * is busy doing someone else's transfer we need that transfer to fully
+ * finish so that we can have the hardware, and to fully finish it needs
+ * the interrupt handler to run. If the interrupts is set to run on the
+ * active CPU this can never happen if interrupts are disabled.
*
- * Return: 0 on success, -EBUSY if client should retry, or an error.
- * Client should have interrupts enabled for a bit before retrying.
+ * Return: 0 on success, -EINVAL on error.
*/
-static int tcs_write(struct rsc_drv *drv, const struct tcs_request *msg)
+int rpmh_rsc_send_data(struct rsc_drv *drv, const struct tcs_request *msg)
{
struct tcs_group *tcs;
int tcs_id;
unsigned long flags;
- int ret;

tcs = get_tcs_for_msg(drv, msg);
if (IS_ERR(tcs))
return PTR_ERR(tcs);

spin_lock_irqsave(&drv->lock, flags);
- /*
- * The h/w does not like if we send a request to the same address,
- * when one is already in-flight or being processed.
- */
- ret = check_for_req_inflight(drv, tcs, msg);
- if (ret)
- goto unlock;

- ret = find_free_tcs(tcs);
- if (ret < 0)
- goto unlock;
- tcs_id = ret;
+ wait_event_lock_irq(drv->tcs_wait,
+ (tcs_id = claim_tcs_for_req(drv, tcs, msg)) >= 0,
+ drv->lock);

tcs->req[tcs_id - tcs->offset] = msg;
set_bit(tcs_id, drv->tcs_in_use);
@@ -627,47 +644,6 @@ static int tcs_write(struct rsc_drv *drv, const struct tcs_request *msg)
__tcs_set_trigger(drv, tcs_id, true);

return 0;
-unlock:
- spin_unlock_irqrestore(&drv->lock, flags);
- return ret;
-}
-
-/**
- * rpmh_rsc_send_data() - Write / trigger active-only message.
- * @drv: The controller.
- * @msg: The data to be sent.
- *
- * NOTES:
- * - This is only used for "ACTIVE_ONLY" since the limitations of this
- * function don't make sense for sleep/wake cases.
- * - To do the transfer, we will grab a whole TCS for ourselves--we don't
- * try to share. If there are none available we'll wait indefinitely
- * for a free one.
- * - This function will not wait for the commands to be finished, only for
- * data to be programmed into the RPMh. See rpmh_tx_done() which will
- * be called when the transfer is fully complete.
- * - This function must be called with interrupts enabled. If the hardware
- * is busy doing someone else's transfer we need that transfer to fully
- * finish so that we can have the hardware, and to fully finish it needs
- * the interrupt handler to run. If the interrupts is set to run on the
- * active CPU this can never happen if interrupts are disabled.
- *
- * Return: 0 on success, -EINVAL on error.
- */
-int rpmh_rsc_send_data(struct rsc_drv *drv, const struct tcs_request *msg)
-{
- int ret;
-
- do {
- ret = tcs_write(drv, msg);
- if (ret == -EBUSY) {
- pr_info_ratelimited("TCS Busy, retrying RPMH message send: addr=%#x\n",
- msg->cmds[0].addr);
- udelay(10);
- }
- } while (ret == -EBUSY);
-
- return ret;
}

/**
@@ -975,6 +951,7 @@ static int rpmh_rsc_probe(struct platform_device *pdev)
return ret;

spin_lock_init(&drv->lock);
+ init_waitqueue_head(&drv->tcs_wait);
bitmap_zero(drv->tcs_in_use, MAX_TCS_NR);

irq = platform_get_irq(pdev, drv->id);

base-commit: b3a9e3b9622ae10064826dccb4f7a52bd88c7407
--
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