| Message ID | 20180208125542.15649-2-vigneshr@ti.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Feb 8, 2018 at 2:55 PM, Vignesh R <vigneshr@ti.com> wrote: > Currently, data in RX FIFO is read based on UART_LSR register state even > if RDI and RLSI interrupts are disabled in UART_IER register. > This is because when IRQ handler is called due to TX FIFO empty event, > RX FIFO is serviced based on UART_LSR register status instead of > UART_IIR status. This defeats the purpose of disabling UART RX > FIFO interrupts during throttling(see, omap_8250_throttle()) as IRQ > handler continues to drain UART RX FIFO resulting in overflow of buffer > at tty layer. > Fix this by making sure that driver drains UART RX FIFO only when > UART_IIR_RDI is set along with UART_LSR_BI or UART_LSR_DR bits. > > Signed-off-by: Vignesh R <vigneshr@ti.com> > - if (status & (UART_LSR_DR | UART_LSR_BI)) { > + if (status & (UART_LSR_DR | UART_LSR_BI) && > + iir & UART_IIR_RDI) { > if (!up->dma || handle_rx_dma(up, iir)) handle_rx_dma() checks for IRQ status as well. But for now it seems we are on safe side since checks are done versus IRQ status with bit 2 set, meaning that iir & RDI will be true. > status = serial8250_rx_chars(up, status); > } Anyway, thanks for the patch, though I need some time to test it on non-OMAP hardware with DMA enabled.
On 08-Feb-18 8:46 PM, Andy Shevchenko wrote: > On Thu, Feb 8, 2018 at 2:55 PM, Vignesh R <vigneshr@ti.com> wrote: >> Currently, data in RX FIFO is read based on UART_LSR register state even >> if RDI and RLSI interrupts are disabled in UART_IER register. >> This is because when IRQ handler is called due to TX FIFO empty event, >> RX FIFO is serviced based on UART_LSR register status instead of >> UART_IIR status. This defeats the purpose of disabling UART RX >> FIFO interrupts during throttling(see, omap_8250_throttle()) as IRQ >> handler continues to drain UART RX FIFO resulting in overflow of buffer >> at tty layer. >> Fix this by making sure that driver drains UART RX FIFO only when >> UART_IIR_RDI is set along with UART_LSR_BI or UART_LSR_DR bits. >> >> Signed-off-by: Vignesh R <vigneshr@ti.com> > >> - if (status & (UART_LSR_DR | UART_LSR_BI)) { >> + if (status & (UART_LSR_DR | UART_LSR_BI) && >> + iir & UART_IIR_RDI) { > >> if (!up->dma || handle_rx_dma(up, iir)) > > handle_rx_dma() checks for IRQ status as well. > > But for now it seems we are on safe side since checks are done versus > IRQ status with bit 2 set, meaning that iir & RDI will be true. > >> status = serial8250_rx_chars(up, status); >> } > > Anyway, thanks for the patch, though I need some time to test it on > non-OMAP hardware with DMA enabled. This patch is needed even when DMA is not enabled. It would be great if you could test this. But, I don't see any other 8250 drivers apart from 8250_omap.c implementing .throttle()/.unthrottle() callbacks. Regards Vignesh
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 1328c7e70108..ffbb955d1c06 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1854,7 +1854,8 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) status = serial_port_in(port, UART_LSR); - if (status & (UART_LSR_DR | UART_LSR_BI)) { + if (status & (UART_LSR_DR | UART_LSR_BI) && + iir & UART_IIR_RDI) { if (!up->dma || handle_rx_dma(up, iir)) status = serial8250_rx_chars(up, status); }
Currently, data in RX FIFO is read based on UART_LSR register state even if RDI and RLSI interrupts are disabled in UART_IER register. This is because when IRQ handler is called due to TX FIFO empty event, RX FIFO is serviced based on UART_LSR register status instead of UART_IIR status. This defeats the purpose of disabling UART RX FIFO interrupts during throttling(see, omap_8250_throttle()) as IRQ handler continues to drain UART RX FIFO resulting in overflow of buffer at tty layer. Fix this by making sure that driver drains UART RX FIFO only when UART_IIR_RDI is set along with UART_LSR_BI or UART_LSR_DR bits. Signed-off-by: Vignesh R <vigneshr@ti.com> --- drivers/tty/serial/8250/8250_port.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)