Re: [PATCH 1/3] mfd: Add support for FTDI FT232H devices

From: Johan Hovold <johan@kernel.org>
To: Anatolij Gustschin <agust@denx.de>
Cc: "Johan Hovold" <johan@kernel.org>, "Bjørn Mork" <bjorn@mork.no>,
	"Lee Jones" <lee.jones@linaro.org>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Alan Tull" <atull@kernel.org>,
	"Moritz Fischer" <moritz.fischer@ettus.com>,
	linux-gpio@vger.kernel.org, linux-fpga@vger.kernel.org,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] mfd: Add support for FTDI FT232H devices
Date: Wed, 12 Jul 2017 10:50:03 +0200	[thread overview]
Message-ID: <20170712085003.GQ29638@localhost> (raw)
In-Reply-To: <20170711085237.4c472621@crub>

On Tue, Jul 11, 2017 at 08:52:37AM +0200, Anatolij Gustschin wrote:
> On Mon, 10 Jul 2017 14:34:27 +0200
> Johan Hovold johan@kernel.org wrote:
> 
> >On Fri, Jul 07, 2017 at 11:53:29AM +0200, Anatolij Gustschin wrote:
> >> On Fri, 07 Jul 2017 09:48:48 +0200
> >> Bjørn Mork bjorn@mork.no wrote:
> >>   
> >> >[adding Johan on the CC list]
> >> >
> >> >Anatolij Gustschin <agust@denx.de> writes:
> >> >  
> >> >> +static struct usb_device_id ftdi_mfd_table[] = {
> >> >> +	{ USB_DEVICE(0x0403, 0x6014) },
> >> >> +	{}
> >> >> +};
> >> >> +MODULE_DEVICE_TABLE(usb, ftdi_mfd_table);    
> >> >
> >> >This device ID is currently handled by the ftdi_sio driver, so I believe
> >> >you at least have to explain how you intend these two drivers to
> >> >cooperate...  
> >> 
> >> these drivers cannot cooperate, the different ftdi function modes
> >> use same device pins as in UART mode. So, you either can use the
> >> device in UART interface mode or in some different mode. I do not
> >> load the ftdi_sio module or do unbind the USB device from the
> >> ftdio_sio driver and bind it to the mfd driver, e.g.:
> >> 
> >>   sh -c "echo -n "3-2:1.0" > /sys/bus/usb/drivers/ftdi_sio/unbind"
> >>   sh -c "echo -n "3-2:1.0" > /sys/bus/usb/drivers/ftdi-mfd/bind"  
> >
> >I'm afraid that's not good enough. If we're going to support a non-UART
> >mode through a separate driver, we need to have all drivers for these
> >devices be able to retrieve the current mode during probe and only bind
> >when the mode matches.
> 
> Can we reliably retrieve the current mode? 

You tell me. ;)

> For devices with connected EEPROM some modes (including UART) are
> configurable in the EEPROM. For devices without EEPROM the default
> mode is always UART, but FIFO-, Bitbang- and MPSSE-mode can be
> switched via commands to the the chip.

IIRC we should be able read from the EEPROM, and I would at least expect
there to be a way to retrieve the current mode as well.

Johan