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

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Date:   Wed, 12 Jul 2017 10:50:03 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Anatolij Gustschin <agust@...x.de>
Cc:     Johan Hovold <johan@...nel.org>,
        Bjørn Mork <bjorn@...k.no>,
        Lee Jones <lee.jones@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alan Tull <atull@...nel.org>,
        Moritz Fischer <moritz.fischer@...us.com>,
        linux-gpio@...r.kernel.org, linux-fpga@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mfd: Add support for FTDI FT232H devices

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@...nel.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@...k.no wrote:
> >>   
> >> >[adding Johan on the CC list]
> >> >
> >> >Anatolij Gustschin <agust@...x.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