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

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Message-ID: <b6392347-c347-137a-d97e-f621b3a7e099@kernel.org>
Date:   Tue, 25 Jan 2022 11:38:05 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Wander Costa <wcosta@...hat.com>
Cc:     Jon Hunter <jonathanh@...dia.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Johan Hovold <johan@...nel.org>,
        Andrew Jeffery <andrew@...id.au>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH] tty: serial: Use fifo in 8250 console driver

On 25. 01. 22, 11:18, Wander Costa wrote:
>> 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
>>
> 
> Indeed I made a mistake here. Independent of the reported this, this
> should be fixed.
> Jiri, do you intend to send an official patch or should I do so?

Please you send the fix after testing the fifo mode still works with 
that fix.

thanks,
-- 
js