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

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Message-ID: <20170719135830.643f853d@crub>
Date:   Wed, 19 Jul 2017 13:58:30 +0200
From:   Anatolij Gustschin <agust@...x.de>
To:     Johan Hovold <johan@...nel.org>
Cc:     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 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.
FT245 FIFO and CBUS GPIO can be switched by a control request, when
FIFO mode is configured in the EEPROM.

>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? 

Thanks,
Anatolij