| Message ID | 20250506112321.61710-4-cuiyunhui@bytedance.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v5,1/4] serial: 8250: fix panic due to PSLVERR | expand |
Hi Ilpo, On Tue, May 6, 2025 at 8:25 PM Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> wrote: > > I think shortlog should include mention to "dummy read" to make it a > bit more specific. > > On Tue, 6 May 2025, Yunhui Cui wrote: > > > In the case of RX_TIMEOUT, to avoid PSLVERR, disable the FIFO > > As with patch 2, please don't assume it is know to the reader how PSLVERR > is triggered. > > > before reading UART_RX when UART_LSR_DR is not set. > > IMO, it would be better to explain the problem better first, something > along these lines: > > DW UART can fire RX_TIMEOUT interrupt without data and remain in that > state forever. dw8250_handle_irq() detects this condition by checking if > UART_LSR_DR is not asserted when RX_TIMEOUT occurred, and if detected, > performs a dummy read to kick DW UART out of this state. > > Performing dummy read from UART_RX is problematic because with ... it lead > to ... > > And only then explain the solution (disable FIFO for while performing of > the dummy read). Okay, thank you. It will be updated in the next version. > > > > > Fixes: 424d79183af0 ("serial: 8250_dw: Avoid "too much work" from bogus rx timeout interrupt") > > Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com> > > --- > > drivers/tty/serial/8250/8250_dw.c | 10 +++++++++- > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c > > index f41c4a9ed58b..ffa8cb10b39c 100644 > > --- a/drivers/tty/serial/8250/8250_dw.c > > +++ b/drivers/tty/serial/8250/8250_dw.c > > @@ -288,9 +288,17 @@ static int dw8250_handle_irq(struct uart_port *p) > > uart_port_lock_irqsave(p, &flags); > > status = serial_lsr_in(up); > > > > - if (!(status & (UART_LSR_DR | UART_LSR_BI))) > > + if (!(status & (UART_LSR_DR | UART_LSR_BI))) { > > + /* To avoid PSLVERR, disable the FIFO first. */ > > + if (up->fcr & UART_FCR_ENABLE_FIFO) > > + serial_out(up, UART_FCR, 0); > > + > > (void) p->serial_in(p, UART_RX); > > > > + if (up->fcr & UART_FCR_ENABLE_FIFO) > > + serial_out(up, UART_FCR, up->fcr); > > + } > > + > > uart_port_unlock_irqrestore(p, flags); > > } > > > > > > -- > i. > Thanks, Yunhui
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index f41c4a9ed58b..ffa8cb10b39c 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -288,9 +288,17 @@ static int dw8250_handle_irq(struct uart_port *p) uart_port_lock_irqsave(p, &flags); status = serial_lsr_in(up); - if (!(status & (UART_LSR_DR | UART_LSR_BI))) + if (!(status & (UART_LSR_DR | UART_LSR_BI))) { + /* To avoid PSLVERR, disable the FIFO first. */ + if (up->fcr & UART_FCR_ENABLE_FIFO) + serial_out(up, UART_FCR, 0); + (void) p->serial_in(p, UART_RX); + if (up->fcr & UART_FCR_ENABLE_FIFO) + serial_out(up, UART_FCR, up->fcr); + } + uart_port_unlock_irqrestore(p, flags); }
In the case of RX_TIMEOUT, to avoid PSLVERR, disable the FIFO before reading UART_RX when UART_LSR_DR is not set. Fixes: 424d79183af0 ("serial: 8250_dw: Avoid "too much work" from bogus rx timeout interrupt") Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com> --- drivers/tty/serial/8250/8250_dw.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)