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Message-ID: <957056a1-78a5-1141-18d7-b49f87fa85f0@linux.intel.com>
Date: Tue, 15 Nov 2022 18:14:50 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Gabriel Somlo <gsomlo@...il.com>
cc: LKML <linux-kernel@...r.kernel.org>,
linux-serial <linux-serial@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>, kgugala@...micro.com,
mholenko@...micro.com, joel@....id.au,
david.abdurachmanov@...il.com, florent@...oy-digital.fr,
geert@...ux-m68k.org
Subject: Re: [PATCH v3 13/14] serial: liteuart: add IRQ support for the TX
path
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@...il.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
> @@ -46,6 +46,7 @@ struct liteuart_port {
> struct uart_port port;
> struct timer_list timer;
> u32 id;
> + bool poll_tx_started;
> };
>
> #define to_liteuart_port(port) container_of(port, struct liteuart_port, port)
> @@ -78,29 +79,24 @@ static void liteuart_putchar(struct uart_port *port, unsigned char ch)
>
> static void liteuart_stop_tx(struct uart_port *port)
> {
> - /* not used in LiteUART, but called unconditionally from serial_core */
Drop this comment from the earlier patch too given you remove it here. It
just adds useless churn in diff for no useful reason.
> + 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?
> + } else {
> + struct liteuart_port *uart = to_liteuart_port(port);
> + uart->poll_tx_started = false;
> + }
> }
>
> static void liteuart_start_tx(struct uart_port *port)
> {
> - struct circ_buf *xmit = &port->state->xmit;
> - unsigned char ch;
> -
> - if (unlikely(port->x_char)) {
> - litex_write8(port->membase + OFF_RXTX, port->x_char);
> - port->icount.tx++;
> - port->x_char = 0;
> - } else if (!uart_circ_empty(xmit)) {
> - while (xmit->head != xmit->tail) {
> - ch = xmit->buf[xmit->tail];
> - xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
> - port->icount.tx++;
This is not based on tty-next tree. Please rebase on top of it (you
might have noted it already, IIRC, somebody noted uart_xmit_advance
conflict in some patch, perhaps it was you :-)).
> - liteuart_putchar(port, ch);
> - }
> + if (port->irq) {
> + u8 irq_mask = litex_read8(port->membase + OFF_EV_ENABLE);
> + litex_write8(port->membase + OFF_EV_ENABLE, irq_mask | EV_TX);
->irq_mask?
> + } else {
> + struct liteuart_port *uart = to_liteuart_port(port);
> + uart->poll_tx_started = true;
> }
> -
> - if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
> - uart_write_wakeup(port);
> }
>
> static void liteuart_stop_rx(struct uart_port *port)
> @@ -131,18 +127,47 @@ static void liteuart_rx_chars(struct uart_port *port)
> tty_flip_buffer_push(&port->state->port);
> }
>
> +static void liteuart_tx_chars(struct uart_port *port)
> +{
> + struct circ_buf *xmit = &port->state->xmit;
> +
> + if (unlikely(port->x_char)) {
> + litex_write8(port->membase + OFF_RXTX, port->x_char);
> + port->x_char = 0;
> + port->icount.tx++;
> + return;
> + }
> +
> + while (!litex_read8(port->membase + OFF_TXFULL)) {
> + if (xmit->head == xmit->tail)
There exists a helper for this condition.
> + break;
> + litex_write8(port->membase + OFF_RXTX, xmit->buf[xmit->tail]);
> + xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
> + port->icount.tx++;
uart_xmit_advance()
> + }
> +
> + if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
> + uart_write_wakeup(port);
> +
> + if (uart_circ_empty(xmit))
> + liteuart_stop_tx(port);
> +}
You might want to check if you can generate this whole function with
Jiri's tx helpers (IIRC, they're only in tty-next tree currently).
> +
> 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);
>
> - /* for now, only rx path triggers interrupts */
> - isr &= EV_RX;
> + if (!(port->irq || uart->poll_tx_started))
> + isr &= ~EV_TX; /* polling mode with tx stopped */
>
> spin_lock(&port->lock);
> if (isr & EV_RX)
> liteuart_rx_chars(port);
> + if (isr & EV_TX) {
> + liteuart_tx_chars(port);
> + }
Extra braces.
> spin_unlock(&port->lock);
>
> return IRQ_RETVAL(isr);
> @@ -196,6 +221,7 @@ static int liteuart_startup(struct uart_port *port)
> }
>
> if (!port->irq) {
> + uart->poll_tx_started = false;
Can poll_tx_started ever be true here?
> timer_setup(&uart->timer, liteuart_timer, 0);
> mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
> }
> @@ -210,6 +236,7 @@ static void liteuart_shutdown(struct uart_port *port)
> struct liteuart_port *uart = to_liteuart_port(port);
>
> litex_write8(port->membase + OFF_EV_ENABLE, 0);
> + uart->poll_tx_started = false;
>
> if (port->irq)
> free_irq(port->irq, port);
>
--
i.
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