Re: [PATCH v4] tty: serial: don't do termios for BTIF

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: sean.wang@mediatek.com, robh+dt@kernel.org, jslaby@suse.com,
	robert.jarzmik@free.fr, arnd@arndb.de, p.zabel@pengutronix.de,
	joel@jms.id.au, david@lechnology.com, jan.kiszka@siemens.com,
	heikki.krogerus@linux.intel.com, hpeter@gmail.com,
	vigneshr@ti.com, matthias.bgg@gmail.com,
	tthayer@opensource.altera.com, devicetree@vger.kernel.org,
	linux-mediatek@lists.infradead.org, linux-serial@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Steven Liu <steven.liu@mediatek.com>,
	Ryder Lee <ryder.lee@mediatek.com>
Subject: Re: [PATCH v4] tty: serial: don't do termios for BTIF
Date: Mon, 29 Jun 2020 11:29:27 +0300	[thread overview]
Message-ID: <20200629082927.GA3703480@smile.fi.intel.com> (raw)
In-Reply-To: <20200627141222.GC1901451@kroah.com>

On Sat, Jun 27, 2020 at 04:12:22PM +0200, Greg KH wrote:
> On Sat, Jun 20, 2020 at 03:59:14AM +0800, sean.wang@mediatek.com wrote:
> > From: Sean Wang <sean.wang@mediatek.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_NTIO' for the unusual unsupported
> > case.
> > 
> > The bluetooth driver would use BTIF device as a serdev. So the termios
> > still function would be called in kernelspace from ttyport_open in
> > drivers/tty/serdev/serdev-ttyprt.c.

> > +#define UART_CAP_NTIO	(1 << 18)	/* UART doesn't do termios */
> 
> Naming is hard.  I will never remember what "NTIO" is, how about we make
> it explicit:
> 	define UART_CAP_IGNORE_TERMIOS
> 
> And the _CAP_ name is getting out of hand, this isn't a "capability",
> it's a "quirk for this port" but that's a battle to worry about later...

For quirks we have a separate field in struct uart_port. Perhaps that can be used?

-- 
With Best Regards,
Andy Shevchenko