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

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Message-ID: <20170725114908.GN2729@localhost>
Date:   Tue, 25 Jul 2017 13:49:08 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Anatolij Gustschin <agust@...x.de>
Cc:     Johan Hovold <johan@...nel.org>, 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,
        David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH 1/3] mfd: Add support for FTDI FT232H devices

On Wed, Jul 19, 2017 at 01:58:30PM +0200, Anatolij Gustschin wrote:
> On Mon, 10 Jul 2017 14:52:10 +0200
> Johan Hovold johan@...nel.org wrote:
> 
> >On Thu, Jul 06, 2017 at 10:49:16PM +0200, Anatolij Gustschin wrote:
> >> Add USB part with common functions for USB-GPIO/I2C/SPI master
> >> adapters. These allow communication with chip's control, transmit
> >> and receive endpoints and will be used by various FT232H drivers.  
> >
> >> +static const struct mfd_cell ftdi_cells[] = {
> >> +	{ .name = "ftdi-cbus-gpio", },
> >> +	{ .name = "ftdi-mpsse-i2c", },
> >> +	{ .name = "ftdi-mpsse-spi", },
> >> +	{ .name = "ftdi-fifo-fpp-mgr", },
> >> +};  
> >
> >Correct me if I'm wrong, but aren't these modes really mutually
> >exclusive, possibly with exception of cbus-gpio (some pins are at least
> >available as GPIOs in MPSSE mode)? Then MFD is not is not the right fit
> >here either.
> 
> MPSSE and FIFO modes are mutually exclusive, but I'm not sure about
> MPSSE and CBUS-GPIO. CBUS-GPIO didn't work as expected when I was
> testing with MPSSE SPI master driver, but maybe it is a driver issue.

Yes, that wasn't clear to me either from just looking at the data
sheets. MPSSE seems to deal with its GPIOs differently.

> FT245 FIFO and CBUS GPIO can be switched by a control request, when
> FIFO mode is configured in the EEPROM.

Since the set_bitmode command is used to control the CBUS gpios, does
that mean that they cannot be toggled independently while FIFO mode is
in use (as the same command is used to set FIFO mode)?

> >And as David Laight already pointed out, your ftdi-fifo-fpp-mgr driver
> >seems too application specific for a generic chip like this.
> 
> Yes, I agree. I'm thinking of a rework to add a FIFO driver instead
> and use it in the fpp-mgr driver. Is that the right direction? 

That sounds better, but I'm still not sure that we would be able to bind
it to devices with the default (generic) VID/PID.

Thanks,
Johan