Hi Marek,
I've got a patch in the same spirit in downstream.
The test campaign reveals performance issues with this patch.
In fact, hard IRQ have been introduced in stm32-usart driver to solve
performance issues due to short FIFO size (16 bytes).
We are currently testing another patch, similar as your RFC proposition,
for RT context.
But results are not ready yet. We can wait them before merging this big
change into driver ?
Thanks,
Valentin
On 12/7/22 20:59, Marek Vasut wrote:
Avoid locking in hard interrupt context, move the entirety of hard IRQ
context code into the threaded IRQ handler. This fixes the following
splat with preempt-rt enabled:
BUG: scheduling while atomic: (mount)/1289/0x00010001
Modules linked in:
Preemption disabled at:
[<c0119127>] irq_enter_rcu+0xb/0x42
CPU: 0 PID: 1289 Comm: (mount) Not tainted 6.1.0-rc7-rt5-stable-standard-00006-gd70aeccb9f0f #17
Hardware name: STM32 (Device Tree Support)
unwind_backtrace from show_stack+0xb/0xc
show_stack from dump_stack_lvl+0x2b/0x34
dump_stack_lvl from __schedule_bug+0x53/0x80
__schedule_bug from __schedule+0x47/0x404
__schedule from schedule_rtlock+0x15/0x34
schedule_rtlock from rtlock_slowlock_locked+0x1d7/0x57e
rtlock_slowlock_locked from rt_spin_lock+0x29/0x3c
rt_spin_lock from stm32_usart_interrupt+0xa9/0x110
stm32_usart_interrupt from __handle_irq_event_percpu+0x73/0x14e
__handle_irq_event_percpu from handle_irq_event_percpu+0x9/0x22
handle_irq_event_percpu from handle_irq_event+0x53/0x76
handle_irq_event from handle_fasteoi_irq+0x65/0xa8
handle_fasteoi_irq from handle_irq_desc+0xf/0x18
handle_irq_desc from gic_handle_irq+0x45/0x54
gic_handle_irq from generic_handle_arch_irq+0x19/0x2c
generic_handle_arch_irq from call_with_stack+0xd/0x10
Signed-off-by: Marek Vasut <marex@xxxxxxx>
---
Cc: Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>
Cc: Erwan Le Ray <erwan.leray@xxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jean Philippe Romain <jean-philippe.romain@xxxxxxxxxxx>
Cc: Jiri Slaby <jirislaby@xxxxxxxxxx>
Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Valentin Caron <valentin.caron@xxxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
To: linux-serial@xxxxxxxxxxxxxxx
---
drivers/tty/serial/stm32-usart.c | 27 +++++++--------------------
1 file changed, 7 insertions(+), 20 deletions(-)
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index a1490033aa164..f5bce0be02676 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -745,14 +745,15 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
}
}
-static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
+static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
{
struct uart_port *port = ptr;
struct tty_port *tport = &port->state->port;
struct stm32_port *stm32_port = to_stm32_port(port);
const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
- u32 sr;
+ unsigned long flags;
unsigned int size;
+ u32 sr;
sr = readl_relaxed(port->membase + ofs->isr);
@@ -792,27 +793,13 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
}
if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch)) {
- spin_lock(&port->lock);
+ spin_lock_irqsave(&port->lock, flags);
stm32_usart_transmit_chars(port);
- spin_unlock(&port->lock);
+ spin_unlock_irqrestore(&port->lock, flags);
}
- if (stm32_usart_rx_dma_enabled(port))
- return IRQ_WAKE_THREAD;
- else
- return IRQ_HANDLED;
-}
-
-static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
-{
- struct uart_port *port = ptr;
- struct tty_port *tport = &port->state->port;
- struct stm32_port *stm32_port = to_stm32_port(port);
- unsigned int size;
- unsigned long flags;
-
/* Receiver timeout irq for DMA RX */
- if (!stm32_port->throttled) {
+ if (stm32_usart_rx_dma_enabled(port) && !stm32_port->throttled) {
spin_lock_irqsave(&port->lock, flags);
size = stm32_usart_receive_chars(port, false);
uart_unlock_and_check_sysrq_irqrestore(port, flags);
@@ -1015,7 +1002,7 @@ static int stm32_usart_startup(struct uart_port *port)
u32 val;
int ret;
- ret = request_threaded_irq(port->irq, stm32_usart_interrupt,
+ ret = request_threaded_irq(port->irq, NULL,
stm32_usart_threaded_interrupt,
IRQF_ONESHOT | IRQF_NO_SUSPEND,
name, port);
