Re: [PATCH v3 13/14] serial: liteuart: add IRQ support for the TX path

Gabriel L. Somlo
2022-11-16T00:16:19Z

On Tue, Nov 15, 2022 at 07:30:09PM +0200, Ilpo Järvinen wrote:
> On Tue, 15 Nov 2022, Gabriel L. Somlo wrote:
>
> > On Tue, Nov 15, 2022 at 06:14:50PM +0200, Ilpo Järvinen wrote:
> > > On Sat, 12 Nov 2022, Gabriel Somlo wrote:
> > >
> > > > Modify the TX path to operate in an IRQ-compatible way, while
> > > > maintaining support for polling mode via the poll timer.
> > > >
> > > > Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
> > > > ---
> > > > drivers/tty/serial/liteuart.c | 67 ++++++++++++++++++++++++-----------
> > > > 1 file changed, 47 insertions(+), 20 deletions(-)
> > > >
> > > > diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
> > > > index e30adb30277f..307c27398e30 100644
> > > > --- a/drivers/tty/serial/liteuart.c
> > > > +++ b/drivers/tty/serial/liteuart.c
>
> > > > + if (port->irq) {
> > > > + u8 irq_mask = litex_read8(port->membase + OFF_EV_ENABLE);
> > > > + litex_write8(port->membase + OFF_EV_ENABLE, irq_mask & ~EV_TX);
> > >
> > > If you put irq_mask into liteuart_port you wouldn't need to read it
> > > back here?
> >
> > So, instead of `bool poll_tx_started` I should just keep a copy of the
> > irq_mask there, and take `&port->lock` whenever I need to *both* update
> > the mask *and* write it out to the actual device register?
>
> I was mostly thinking of storing EV_RX there but then it could be derived
> from port->irq that is checked by all paths already.

So, just to clear up the best course of action here (before I rebase
everything on top of tty-next: How about the patch below (currently
applied separately at the end of the entire series, but I can respin
it as part of the rx path (12/14) and tx path (13/14) as appropriate.

Let me know what you think.

Thanks,
--Gabriel

diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
index eb0ae8c8bd94..185db423c65f 100644
--- a/drivers/tty/serial/liteuart.c
+++ b/drivers/tty/serial/liteuart.c
@@ -47,7 +47,7 @@ struct liteuart_port {
struct uart_port port;
struct timer_list timer;
u32 id;
- bool poll_tx_started;
+ u8 irq_reg;
};

#define to_liteuart_port(port) container_of(port, struct liteuart_port, port)
@@ -70,26 +70,27 @@ static struct uart_driver liteuart_driver = {
#endif
};

+static void liteuart_update_irq_reg(struct uart_port *port, bool set, u8 bits)
+{
+ struct liteuart_port *uart = to_liteuart_port(port);
+
+ if (set)
+ uart->irq_reg |= bits;
+ else
+ uart->irq_reg &= ~bits;
+
+ if (port->irq)
+ litex_write8(port->membase + OFF_EV_ENABLE, uart->irq_reg);
+}
+
static void liteuart_stop_tx(struct uart_port *port)
{
- if (port->irq) {
- u8 irq_mask = litex_read8(port->membase + OFF_EV_ENABLE);
- litex_write8(port->membase + OFF_EV_ENABLE, irq_mask & ~EV_TX);
- } else {
- struct liteuart_port *uart = to_liteuart_port(port);
- uart->poll_tx_started = false;
- }
+ liteuart_update_irq_reg(port, false, EV_TX);
}

static void liteuart_start_tx(struct uart_port *port)
{
- if (port->irq) {
- u8 irq_mask = litex_read8(port->membase + OFF_EV_ENABLE);
- litex_write8(port->membase + OFF_EV_ENABLE, irq_mask | EV_TX);
- } else {
- struct liteuart_port *uart = to_liteuart_port(port);
- uart->poll_tx_started = true;
- }
+ liteuart_update_irq_reg(port, true, EV_TX);
}

static void liteuart_stop_rx(struct uart_port *port)
@@ -149,12 +150,10 @@ static irqreturn_t liteuart_interrupt(int irq, void *data)
{
struct liteuart_port *uart = data;
struct uart_port *port = &uart->port;
- u8 isr = litex_read8(port->membase + OFF_EV_PENDING);
-
- if (!(port->irq || uart->poll_tx_started))
- isr &= ~EV_TX; /* polling mode with tx stopped */
+ u8 isr;

spin_lock(&port->lock);
+ isr = litex_read8(port->membase + OFF_EV_PENDING) & uart->irq_reg;
if (isr & EV_RX)
liteuart_rx_chars(port);
if (isr & EV_TX)
@@ -195,39 +194,40 @@ static unsigned int liteuart_get_mctrl(struct uart_port *port)
static int liteuart_startup(struct uart_port *port)
{
struct liteuart_port *uart = to_liteuart_port(port);
+ unsigned long flags;
int ret;
- u8 irq_mask = 0;

if (port->irq) {
ret = request_irq(port->irq, liteuart_interrupt, 0,
KBUILD_MODNAME, uart);
- if (ret == 0) {
- /* only enabling rx interrupts at startup */
- irq_mask = EV_RX;
- } else {
+ if (ret) {
pr_err(pr_fmt("line %d irq %d failed: using polling\n"),
port->line, port->irq);
port->irq = 0;
}
}

+ spin_lock_irqsave(&port->lock, flags);
+ /* only enabling rx irqs during startup */
+ liteuart_update_irq_reg(port, true, EV_RX);
+ spin_unlock_irqrestore(&port->lock, flags);
+
if (!port->irq) {
- uart->poll_tx_started = false;
timer_setup(&uart->timer, liteuart_timer, 0);
mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
}

- litex_write8(port->membase + OFF_EV_ENABLE, irq_mask);
-
return 0;
}

static void liteuart_shutdown(struct uart_port *port)
{
struct liteuart_port *uart = to_liteuart_port(port);
+ unsigned long flags;

- litex_write8(port->membase + OFF_EV_ENABLE, 0);
- uart->poll_tx_started = false;
+ spin_lock_irqsave(&port->lock, flags);
+ liteuart_update_irq_reg(port, false, EV_RX | EV_TX);
+ spin_unlock_irqrestore(&port->lock, flags);

if (port->irq)
free_irq(port->irq, port);
--
2.37.3