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

MICRONOVA SRL
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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);
> }
>

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