* Vikram Pandita <vikram.pandita@xxxxxx> [091116 15:00]:
> OMAP3630 and OMAP4430 UART IP blocks have a restriction wrt RX FIFO.
> Empty RX fifo read causes an abort. OMAP1/2/3 do not have this restriction.
>
> So interoduce a flag in 8250 driver: UPF_NO_EMPTY_FIFO_READ
>
> If this flag is specified for an 8250 port, then first check if rx fifo has
> contents, and only then proceed to read the fifo.
>
> The change affects only boards passing this flag in port data and hence is
> non-disruptive for other boards.
>
> First reported/fixed on omap4430 by Shilimkar, Santosh
This should go to linux-serial@xxxxxxxxxxxxxxx and Alan Cox.
Regards,
Tony
> Signed-off-by: Vikram Pandita <vikram.pandita@xxxxxx>
> Cc: Shilimkar, Santosh <santosh.shilimkar@xxxxxx>
> ---
> drivers/serial/8250.c | 30 +++++++++++++++++++++++++-----
> include/linux/serial_core.h | 1 +
> 2 files changed, 26 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
> index 737b4c9..03c890e 100644
> --- a/drivers/serial/8250.c
> +++ b/drivers/serial/8250.c
> @@ -1245,7 +1245,11 @@ static void autoconfig(struct uart_8250_port *up, unsigned int probeflags)
> #endif
> serial_outp(up, UART_MCR, save_mcr);
> serial8250_clear_fifos(up);
> - serial_in(up, UART_RX);
> + if (up->port.flags & UPF_NO_EMPTY_FIFO_READ) {
> + if (serial_inp(up, UART_LSR) & UART_LSR_DR)
> + serial_in(up, UART_RX);
> + } else
> + serial_in(up, UART_RX);
> if (up->capabilities & UART_CAP_UUE)
> serial_outp(up, UART_IER, UART_IER_UUE);
> else
> @@ -1289,7 +1293,11 @@ static void autoconfig_irq(struct uart_8250_port *up)
> }
> serial_outp(up, UART_IER, 0x0f); /* enable all intrs */
> (void)serial_inp(up, UART_LSR);
> - (void)serial_inp(up, UART_RX);
> + if (up->port.flags & UPF_NO_EMPTY_FIFO_READ) {
> + if (serial_inp(up, UART_LSR) & UART_LSR_DR)
> + (void)serial_inp(up, UART_RX);
> + } else
> + (void)serial_inp(up, UART_RX);
> (void)serial_inp(up, UART_IIR);
> (void)serial_inp(up, UART_MSR);
> serial_outp(up, UART_TX, 0xFF);
> @@ -1984,7 +1992,11 @@ static int serial8250_startup(struct uart_port *port)
> * Clear the interrupt registers.
> */
> (void) serial_inp(up, UART_LSR);
> - (void) serial_inp(up, UART_RX);
> + if (up->port.flags & UPF_NO_EMPTY_FIFO_READ) {
> + if (serial_inp(up, UART_LSR) & UART_LSR_DR)
> + (void) serial_inp(up, UART_RX);
> + } else
> + (void) serial_inp(up, UART_RX);
> (void) serial_inp(up, UART_IIR);
> (void) serial_inp(up, UART_MSR);
>
> @@ -2141,7 +2153,11 @@ dont_test_tx_en:
> * routines or the previous session.
> */
> serial_inp(up, UART_LSR);
> - serial_inp(up, UART_RX);
> + if (up->port.flags & UPF_NO_EMPTY_FIFO_READ) {
> + if (serial_inp(up, UART_LSR) & UART_LSR_DR)
> + serial_inp(up, UART_RX);
> + } else
> + serial_inp(up, UART_RX);
> serial_inp(up, UART_IIR);
> serial_inp(up, UART_MSR);
> up->lsr_saved_flags = 0;
> @@ -2207,7 +2223,11 @@ static void serial8250_shutdown(struct uart_port *port)
> * Read data port to reset things, and then unlink from
> * the IRQ chain.
> */
> - (void) serial_in(up, UART_RX);
> + if (up->port.flags & UPF_NO_EMPTY_FIFO_READ) {
> + if (serial_inp(up, UART_LSR) & UART_LSR_DR)
> + (void) serial_inp(up, UART_RX);
> + } else
> + (void) serial_in(up, UART_RX);
>
> del_timer_sync(&up->timer);
> up->timer.function = serial8250_timeout;
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index db532ce..0d65bb3 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -308,6 +308,7 @@ struct uart_port {
> #define UPF_SPD_WARP ((__force upf_t) (0x1010))
> #define UPF_SKIP_TEST ((__force upf_t) (1 << 6))
> #define UPF_AUTO_IRQ ((__force upf_t) (1 << 7))
> +#define UPF_NO_EMPTY_FIFO_READ ((__force upf_t) (1 << 8))
> #define UPF_HARDPPS_CD ((__force upf_t) (1 << 11))
> #define UPF_LOW_LATENCY ((__force upf_t) (1 << 13))
> #define UPF_BUGGY_UART ((__force upf_t) (1 << 14))
> --
> 1.6.5.1.69.g36942
>
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