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