linux-kernel - Re: [PATCH v5 12/14] serial: liteuart: add IRQ support for the RX path

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Date:   Mon, 21 Nov 2022 09:54:34 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Gabriel Somlo <gsomlo@...il.com>, linux-kernel@...r.kernel.org
Cc:     linux-serial@...r.kernel.org, gregkh@...uxfoundation.org,
        kgugala@...micro.com, mholenko@...micro.com, joel@....id.au,
        david.abdurachmanov@...il.com, florent@...oy-digital.fr,
        geert@...ux-m68k.org, ilpo.jarvinen@...ux.intel.com
Subject: Re: [PATCH v5 12/14] serial: liteuart: add IRQ support for the RX
 path

On 18. 11. 22, 15:55, Gabriel Somlo wrote:
> Add support for IRQ-driven RX. Support for the TX path will be added
> in a separate commit.
> 
> Signed-off-by: Gabriel Somlo <gsomlo@...il.com>
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
> 
> Changes from v4:
>    - using dev_err() instead of a combo of pr_err() and pr_fmt()
>    - dropped "get irq" comment in probe()
> 
>> Changes from v3:
>>    - add shadow irq register to support polling mode and avoid reading
>>      hardware mmio irq register to learn which irq flags are enabled
>>      - this also simplifies both liteuart_interrupt() and liteuart_startup()
> 
>   drivers/tty/serial/liteuart.c | 76 +++++++++++++++++++++++++++++++----
>   1 file changed, 69 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
> index 8a6e176be08e..678c37c952cf 100644
> --- a/drivers/tty/serial/liteuart.c
> +++ b/drivers/tty/serial/liteuart.c
> @@ -7,6 +7,7 @@
>   
>   #include <linux/bits.h>
>   #include <linux/console.h>
> +#include <linux/interrupt.h>
>   #include <linux/litex.h>
>   #include <linux/module.h>
>   #include <linux/of.h>
> @@ -46,6 +47,7 @@ struct liteuart_port {
>   	struct uart_port port;
>   	struct timer_list timer;
>   	u32 id;
> +	u8 irq_reg;
>   };
>   
>   #define to_liteuart_port(port)	container_of(port, struct liteuart_port, port)
> @@ -76,6 +78,19 @@ static void liteuart_putchar(struct uart_port *port, unsigned char ch)
>   	litex_write8(port->membase + OFF_RXTX, ch);
>   }
>   
> +static void liteuart_update_irq_reg(struct uart_port *port, bool set, u8 mask)
> +{
> +	struct liteuart_port *uart = to_liteuart_port(port);
> +
> +	if (set)
> +		uart->irq_reg |= mask;
> +	else
> +		uart->irq_reg &= ~mask;
> +
> +	if (port->irq)
> +		litex_write8(port->membase + OFF_EV_ENABLE, uart->irq_reg);
> +}
> +
>   static void liteuart_stop_tx(struct uart_port *port)
>   {
>   }
> @@ -129,13 +144,27 @@ static void liteuart_rx_chars(struct uart_port *port)
>   	tty_flip_buffer_push(&port->state->port);
>   }
>   
> +static irqreturn_t liteuart_interrupt(int irq, void *data)
> +{
> +	struct liteuart_port *uart = data;
> +	struct uart_port *port = &uart->port;
> +	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);
> +	spin_unlock(&port->lock);
> +
> +	return IRQ_RETVAL(isr);
> +}
> +
>   static void liteuart_timer(struct timer_list *t)
>   {
>   	struct liteuart_port *uart = from_timer(uart, t, timer);
>   	struct uart_port *port = &uart->port;
>   
> -	liteuart_rx_chars(port);
> -
> +	liteuart_interrupt(0, port);

Are you sure spin_lock() is safe from this path? I assume so, but have 
you thought about it?

>   	mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
>   }
>   
> @@ -161,19 +190,46 @@ 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;
>   
> -	/* disable events */
> -	litex_write8(port->membase + OFF_EV_ENABLE, 0);
> +	if (port->irq) {
> +		ret = request_irq(port->irq, liteuart_interrupt, 0,
> +				  KBUILD_MODNAME, uart);

Just asking: cannot the irq be shared?

> +		if (ret) {
> +			dev_err(port->dev,
> +				"line %d irq %d failed: switch to polling\n",
> +				port->line, port->irq);

That is, it should be only dev_warn(), or?

> +			port->irq = 0;
> +		}
> +	}

thanks,
-- 
js
suse labs