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Date: Mon, 4 Jun 2018 20:40:29 +0300
From: "Matwey V. Kornilov" <matwey.kornilov@...il.com>
To: Giulio Benetti <giulio.benetti@...ronovasrl.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jslaby@...e.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Kees Cook <keescook@...omium.org>,
Matthias Brugger <mbrugger@...e.com>,
Allen Pais <allen.lkml@...il.com>, Sean Young <sean@...s.org>,
Ed Blake <ed.blake@...drel.com>,
Stefan Potyra <Stefan.Potyra@...ktrobit.com>,
Philipp Zabel <p.zabel@...gutronix.de>,
Joshua Scott <joshua.scott@...iedtelesis.co.nz>,
Vignesh R <vigneshr@...com>,
Rolf Evers-Fischer <rolf.evers.fischer@...iv.com>,
Aaron Sierra <asierra@...-inc.com>,
Rafael Gago <rafael.gago@...il.com>,
Joel Stanley <joel@....id.au>,
Sean Wang <sean.wang@...iatek.com>,
linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] serial: 8250: Handle case port doesn't have TEMT
interrupt using em485.
01.06.2018 15:40, Giulio Benetti пишет:
> Some 8250 ports only have TEMT interrupt, so current implementation
> can't work for ports without it. The only chance to make it work is to
> loop-read on LSR register.
>
> With NO TEMT interrupt check if both TEMT and THRE are set looping on
> LSR register.
>
> Signed-off-by: Giulio Benetti <giulio.benetti@...ronovasrl.com>
> ---
> drivers/tty/serial/8250/8250.h | 2 +-
> drivers/tty/serial/8250/8250_dw.c | 2 +-
> drivers/tty/serial/8250/8250_omap.c | 2 +-
> drivers/tty/serial/8250/8250_port.c | 26 ++++++++++++++++++--------
> include/linux/serial_8250.h | 1 +
> 5 files changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index ebfb0bd5bef5..5c6ae5f69432 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -136,7 +136,7 @@ void serial8250_rpm_put(struct uart_8250_port *p);
> void serial8250_rpm_get_tx(struct uart_8250_port *p);
> void serial8250_rpm_put_tx(struct uart_8250_port *p);
>
> -int serial8250_em485_init(struct uart_8250_port *p);
> +int serial8250_em485_init(struct uart_8250_port *p, bool has_temt_isr);
> void serial8250_em485_destroy(struct uart_8250_port *p);
>
> static inline void serial8250_out_MCR(struct uart_8250_port *up, int value)
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index 0f8b4da03d4e..888280ff5451 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -330,7 +330,7 @@ static int dw8250_rs485_config(struct uart_port *p,
> * are idempotent
> */
> if (rs485->flags & SER_RS485_ENABLED) {
> - int ret = serial8250_em485_init(up);
> + int ret = serial8250_em485_init(up, false);
>
> if (ret) {
> rs485->flags &= ~SER_RS485_ENABLED;
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 624b501fd253..ab483c8b30c8 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -725,7 +725,7 @@ static int omap_8250_rs485_config(struct uart_port *port,
> * are idempotent
> */
> if (rs485->flags & SER_RS485_ENABLED) {
> - int ret = serial8250_em485_init(up);
> + int ret = serial8250_em485_init(up, true);
>
> if (ret) {
> rs485->flags &= ~SER_RS485_ENABLED;
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 95833cbc4338..e14badbbf181 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -599,15 +599,16 @@ EXPORT_SYMBOL_GPL(serial8250_rpm_put);
> /**
> * serial8250_em485_init() - put uart_8250_port into rs485 emulating
> * @p: uart_8250_port port instance
> + * @p: bool specify if 8250 port has TEMT interrupt or not
> *
> * The function is used to start rs485 software emulating on the
> * &struct uart_8250_port* @p. Namely, RTS is switched before/after
> * transmission. The function is idempotent, so it is safe to call it
> * multiple times.
> *
> - * The caller MUST enable interrupt on empty shift register before
> - * calling serial8250_em485_init(). This interrupt is not a part of
> - * 8250 standard, but implementation defined.
> + * If has_temt_isr is passed as true, the caller MUST enable interrupt
> + * on empty shift register before calling serial8250_em485_init().
> + * This interrupt is not a part of 8250 standard, but implementation defined.
> *
> * The function is supposed to be called from .rs485_config callback
> * or from any other callback protected with p->port.lock spinlock.
> @@ -616,7 +617,7 @@ EXPORT_SYMBOL_GPL(serial8250_rpm_put);
> *
> * Return 0 - success, -errno - otherwise
> */
> -int serial8250_em485_init(struct uart_8250_port *p)
> +int serial8250_em485_init(struct uart_8250_port *p, bool has_temt_isr)
> {
> if (p->em485)
> return 0;
> @@ -633,6 +634,7 @@ int serial8250_em485_init(struct uart_8250_port *p)
> p->em485->start_tx_timer.function = &serial8250_em485_handle_start_tx;
> p->em485->port = p;
> p->em485->active_timer = NULL;
> + p->em485->has_temt_isr = has_temt_isr;
> serial8250_em485_rts_after_send(p);
>
> return 0;
> @@ -1517,11 +1519,19 @@ 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 (em485->has_temt_isr) {
> + if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
> + return;
> + } else {
> + while ((lsr & BOTH_EMPTY) != BOTH_EMPTY) {
> + lsr = serial_in(p, UART_LSR);
> + cpu_relax();
> + }
What happens if TEMP never be empty after interruption occurring?
> + }
>
> em485->active_timer = NULL;
>
> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
> index a27ef5f56431..9b13cf59726b 100644
> --- a/include/linux/serial_8250.h
> +++ b/include/linux/serial_8250.h
> @@ -83,6 +83,7 @@ struct uart_8250_em485 {
> struct hrtimer start_tx_timer; /* "rs485 start tx" timer */
> struct hrtimer stop_tx_timer; /* "rs485 stop tx" timer */
> struct hrtimer *active_timer; /* pointer to active timer */
> + bool has_temt_isr; /* say if 8250 has TEMT interrupt or no */
> struct uart_8250_port *port; /* for hrtimer callbacks */
> };
>
>
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