linux-kernel - Re: [PATCH v2] tty: serial: don't do termios for BTIF

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Date:   Mon, 20 Apr 2020 13:46:24 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     sean.wang@...iatek.com
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com,
        robert.jarzmik@...e.fr, arnd@...db.de, p.zabel@...gutronix.de,
        joel@....id.au, david@...hnology.com, jan.kiszka@...mens.com,
        heikki.krogerus@...ux.intel.com, hpeter@...il.com, vigneshr@...com,
        matthias.bgg@...il.com, tthayer@...nsource.altera.com,
        linux-mediatek@...ts.infradead.org, linux-serial@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Steven Liu <steven.liu@...iatek.com>,
        Ryder Lee <ryder.lee@...iatek.com>
Subject: Re: [PATCH v2] tty: serial: don't do termios for BTIF

On Mon, Apr 20, 2020 at 10:06:38AM +0800, sean.wang@...iatek.com wrote:
> From: Sean Wang <sean.wang@...iatek.com>
> 
> Bluetooth Interface (BTIF) is designed dedicatedly for MediaTek SOC with
> BT in order to be instead of the UART interface between BT module and Host
> CPU, and not exported to user space to access.
> 
> As the UART design, BTIF will be an APB slave and can transmit or receive
> data by MCU access, but doesn't provide termios function like baudrate and
> flow control setup.
> 
> Even LCR on offset 0xC that is just a FAKELCR
> a. If FAKELCR[7] is equaled to 1, RBR(0x00), THR(0x00), IER(0x04)
>    will not be readable/writable.
> 
> b. If FAKELCR is equaled to 0xBF, RBR(0x00), THR(0x00), IER(0x04),
>    IIR(0x08), and LSR(0x14) will not be readable/writable.
> 
> So adding a new capability 'UART_CAP_NMOD' for the unusual unsupported
> case.

...

> +#define UART_CAP_NMOD	(1 << 18)	/* UART doesn't do termios */

I would rather spell it as NTIO or NO_TIO (as TIO is a well established prefix
for termios IOCTLs).


-- 
With Best Regards,
Andy Shevchenko