Re: [PATCH v2 4/7] serial: 8250: Handle implementations not having TEMT interrupt using em485

[Giulio Benetti <giulio.benetti@micronovasrl.com>]

Hi Heiko,

very cleaner way to handle TEMT as a capability!
And I've found one thing...

Il 26/03/2020 00:14, Heiko Stuebner ha scritto:
> From: Giulio Benetti <giulio.benetti@micronovasrl.com>
> 
> Some 8250 ports have a TEMT interrupt but it's not a part of the 8250
> standard, instead only available on some implementations.
> 
> The current em485 implementation does not work on ports without it.
> The only chance to make it work is to loop-read on LSR register.
> 
> So add UART_CAP_TEMT to mark 8250 uarts having this interrupt,
> update all current em485 users with that capability and make
> the stop_tx function loop-read on uarts not having it.
> 
> Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
> [moved to use added UART_CAP_TEMT, use readx_poll_timeout]
> Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
> ---
>   drivers/tty/serial/8250/8250.h            |  1 +
>   drivers/tty/serial/8250/8250_bcm2835aux.c |  2 +-
>   drivers/tty/serial/8250/8250_of.c         |  2 ++
>   drivers/tty/serial/8250/8250_omap.c       |  2 +-
>   drivers/tty/serial/8250/8250_port.c       | 25 +++++++++++++++++++----
>   5 files changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index 52bb21205bb6..770eb00db497 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -82,6 +82,7 @@ struct serial8250_config {
>   #define UART_CAP_MINI	(1 << 17)	/* Mini UART on BCM283X family lacks:
>   					 * STOP PARITY EPAR SPAR WLEN5 WLEN6
>   					 */
> +#define UART_CAP_TEMT	(1 << 18)	/* UART has TEMT interrupt */
>   
>   #define UART_BUG_QUOT	(1 << 0)	/* UART has buggy quot LSB */
>   #define UART_BUG_TXEN	(1 << 1)	/* UART has buggy TX IIR status */
> diff --git a/drivers/tty/serial/8250/8250_bcm2835aux.c b/drivers/tty/serial/8250/8250_bcm2835aux.c
> index 12d03e678295..3881242424ca 100644
> --- a/drivers/tty/serial/8250/8250_bcm2835aux.c
> +++ b/drivers/tty/serial/8250/8250_bcm2835aux.c
> @@ -91,7 +91,7 @@ static int bcm2835aux_serial_probe(struct platform_device *pdev)
>   		return -ENOMEM;
>   
>   	/* initialize data */
> -	up.capabilities = UART_CAP_FIFO | UART_CAP_MINI;
> +	up.capabilities = UART_CAP_FIFO | UART_CAP_MINI | UART_CAP_TEMT;
>   	up.port.dev = &pdev->dev;
>   	up.port.regshift = 2;
>   	up.port.type = PORT_16550;
> diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c
> index 65e9045dafe6..841f6fcb2878 100644
> --- a/drivers/tty/serial/8250/8250_of.c
> +++ b/drivers/tty/serial/8250/8250_of.c
> @@ -225,6 +225,8 @@ static int of_platform_serial_probe(struct platform_device *ofdev)
>   			&port8250.overrun_backoff_time_ms) != 0)
>   		port8250.overrun_backoff_time_ms = 0;
>   
> +	port8250.capabilities |= UART_CAP_TEMT;
> +

Shouldn't this be NOT UART_CAP_TEMT set by default? On all other
vendor specific files you enable it, I think here you shouldn't enable
it too by default. Right?

Best regards
-- 
Giulio Benetti
CTO

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>   	ret = serial8250_register_8250_port(&port8250);
>   	if (ret < 0)
>   		goto err_dispose;
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index dd69226ce918..d29d5b0cf8c1 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -1140,7 +1140,7 @@ static int omap8250_probe(struct platform_device *pdev)
>   	up.port.regshift = 2;
>   	up.port.fifosize = 64;
>   	up.tx_loadsz = 64;
> -	up.capabilities = UART_CAP_FIFO;
> +	up.capabilities = UART_CAP_FIFO | UART_CAP_TEMT;
>   #ifdef CONFIG_PM
>   	/*
>   	 * Runtime PM is mostly transparent. However to do it right we need to a
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 47c059987538..41ad7db6a31e 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -15,6 +15,7 @@
>   #include <linux/moduleparam.h>
>   #include <linux/ioport.h>
>   #include <linux/init.h>
> +#include <linux/iopoll.h>
>   #include <linux/console.h>
>   #include <linux/sysrq.h>
>   #include <linux/delay.h>
> @@ -1520,6 +1521,11 @@ static inline void __do_stop_tx(struct uart_8250_port *p)
>   		serial8250_rpm_put_tx(p);
>   }
>   
> +static inline int __get_lsr(struct uart_8250_port *p)
> +{
> +	return serial_in(p, UART_LSR);
> +}
> +
>   static inline void __stop_tx(struct uart_8250_port *p)
>   {
>   	struct uart_8250_em485 *em485 = p->em485;
> @@ -1529,11 +1535,22 @@ static inline void __stop_tx(struct uart_8250_port *p)
>   		/*
>   		 * To provide required timeing and allow FIFO transfer,
>   		 * __stop_tx_rs485() must be called only when both FIFO and
> -		 * shift register are empty. It is for device driver to enable
> -		 * interrupt on TEMT.
> +		 * shift register are empty. If 8250 port supports it,
> +		 * it is for device driver to enable interrupt on TEMT.
> +		 * Otherwise must loop-read until TEMT and THRE flags are set.
>   		 */
> -		if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
> -			return;
> +		if (p->capabilities & UART_CAP_TEMT) {
> +			if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
> +				return;
> +		} else {
> +			int lsr;
> +
> +			if (readx_poll_timeout(__get_lsr, p, lsr,
> +					(lsr & BOTH_EMPTY) == BOTH_EMPTY,
> +					0, 10000) < 0)
> +				pr_warn("%s: timeout waiting for fifos to empty\n",
> +					p->port.name);
> +		}
>   
>   		__stop_tx_rs485(p);
>   	}
>