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

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Message-ID: <20200629084051.GA1234189@kroah.com>
Date:   Mon, 29 Jun 2020 10:40:51 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     sean.wang@...iatek.com, robh+dt@...nel.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,
        devicetree@...r.kernel.org, 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 v4] tty: serial: don't do termios for BTIF

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@...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_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