Re: [PATCH] tty: serial: Use fifo in 8250 console driver

[Jon Hunter]

On 25/01/2022 09:36, Jiri Slaby wrote:

...

> > 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. Unfortunately, this did not fix it. The port type is PORT_TEGRA ...

 70006000.serial: ttyS0 at MMIO 0x70006000 (irq = 72, base_baud = 25500000) is a Tegra

Jon

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