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Date:   Mon, 29 Jun 2020 10:40:51 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
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
Message-ID: <20200629084051.GA1234189@kroah.com>
References: <78efa2b1e2599deff4d838b05b4054ec5ac2976a.1592595601.git.sean.wang@mediatek.com>
 <20200627141222.GC1901451@kroah.com>
 <20200629082927.GA3703480@smile.fi.intel.com>
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On Mon, Jun 29, 2020 at 11:29:27AM +0300, Andy Shevchenko wrote:
> 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?

That would be much nicer, if possible.

thanks,

greg k-h