Messages in this thread Patch in this message | | | Date | Tue, 25 Jan 2022 10:36:27 +0100 | Subject | Re: [PATCH] tty: serial: Use fifo in 8250 console driver | From | Jiri Slaby <> |
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On 25. 01. 22, 10:08, Jiri Slaby wrote: > On 25. 01. 22, 9:39, Jon Hunter wrote: >> >> On 29/10/2021 21:14, wander@redhat.com wrote: >>> From: Wander Lairson Costa <wander@redhat.com> >>> >>> Note: I am using a small test app + driver located at [0] for the >>> problem description. serco is a driver whose write function dispatches >>> to the serial controller. sertest is a user-mode app that writes n bytes >>> to the serial console using the serco driver. ... >>> Signed-off-by: Wander Lairson Costa <wander@redhat.com> >> >> >> On the current mainline and -next branches, I have noticed that the >> serial output on many of our Tegra boards is corrupted and so >> parsing the serial output is failing. >> >> Before this change the serial console would appear as follows ... >> >> [ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x411fd071] >> [ 0.000000] Linux version 5.16.0-rc6-00091-gadbfddc757ae >> (jonathanh@jonathanh-vm-01) (aarch64-linux-gnu-gcc (Linaro GCC >> 6.4-2017.08) 6.4.1 20170707, GNU ld (Linaro_Binutils-2017.08) >> 2.27.0.20161019) #15 SMP PREEMPT Tue Jan 25 00:15:25 PST 2022 >> [ 0.000000] Machine model: NVIDIA Jetson TX1 Developer Kit >> >> And now I see ... >> >> [ 0.000000] Booting Linux on physicalfd071] >> [ 0.000000] Linux version 5.16.0-rc6-athanh@j-linux-g017.08) >> Linaro_B20161019n 25 00:[ 0.000000] Machine model: NVIDIA Jet[ >> 0.000000] efi: UEFI not found. >> [ 0.000000] NUMA: No NUMA configurati[ 0.000000] NUMA: Faking a >> node at [m00000001[ 0.000000] NUMA: NODE_DATA [mem 0x17[ >> 0.000000] Zone ranges: >> >> Bisecting is pointing to this commit. Let me know if there are any >> tests I can run. Otherwise we may need to disable this at least >> for Tegra. > > > The test is bogus: > use_fifo = (up->capabilities & UART_CAP_FIFO) && > port->fifosize > 1 && > (serial_port_in(port, UART_FCR) & UART_FCR_ENABLE_FIFO) > > FCR is write only. Reading it, one gets IIR contents.
In particular, the test is checking whether there is no interrupt pending (UART_FCR_ENABLE_FIFO == UART_IIR_NO_INT). So it oscillates between use_fifo and not, depending on the interrupt state of the chip.
Could you change it into something like this: --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -3396,7 +3396,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
use_fifo = (up->capabilities & UART_CAP_FIFO) && port->fifosize > 1 && - (serial_port_in(port, UART_FCR) & UART_FCR_ENABLE_FIFO) && + (up->fcr & UART_FCR_ENABLE_FIFO) && /* * After we put a data in the fifo, the controller will send * it regardless of the CTS state. Therefore, only use fifo
And see whether it fixes the issue. Anyway, of what port type is the serial port (what says dmesg/setserial about that)?
thanks, -- js suse labs
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