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Subject: Re: [PATCH v2] usb: serial: Repair FTDI FT232R bricked eeprom
To:     James Hilliard <james.hilliard1@gmail.com>,
        Oliver Neukum <oneukum@suse.de>
CC:     linux-usb@vger.kernel.org, Johan Hovold <johan@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Russ Dill <Russ.Dill@gmail.com>
From:   "Hector Martin \"marcan\"" <hector@marcansoft.com>
Message-ID: <36F0CEB4-DE2E-41DA-9569-4706B00FCF7D@marcansoft.com>
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On September 10, 2020 12:40:59 PM GMT+09:00, James Hilliard <james.hilliard1@gmail.com> wrote:
>On Wed, Sep 9, 2020 at 9:02 PM Oliver Neukum <oneukum@suse.de> wrote:
>>
>> Am Mittwoch, den 09.09.2020, 13:34 -0600 schrieb James Hilliard:
>> > This patch detects and reverses the effects of the malicious FTDI
>> > Windows driver version 2.12.00(FTDIgate).
>>
>> Hi,
>>
>> this raises questions.
>> Should we do this unconditionally without asking?
>Well I think since we can reliably detect devices that have been
>bricked by the malicious windows driver it's fine. I was careful to
>ensure that this will bail out and not try to change anything unless
>all
>conditions match this specific brick attack.
>> Does this belong into kernel space?
>This seemed to be by far the simplest option for embedded systems
>that need to automatically detect and repair the bricked eeproms.
>
>People seem to have plugged a bunch of counterfeit FTDI Arduino's
>that normally attach to an embedded Linux host into windows for
>some reason for a kiosk platform of mine which messed up the
>userspace detection/mappings. This seemed like the best way to
>avoid this being a support issue requiring manual unbricking
>prochedures.

If you need to update the kernel on this platform anyway to use this feature, why not just introduce a userspace script to fix the bricked units instead?

Needing this autofixed seems like somewhat of a niche use case better served by a script on platforms where it might be a problem, rather than upstream kernel code.

>>
>> > +static int ftdi_repair_brick(struct usb_serial_port *port)
>> > +{
>> > +     struct ftdi_private *priv = usb_get_serial_port_data(port);
>> > +     int orig_latency;
>> > +     int rv;
>> > +     u16 *eeprom_data;
>> > +     u16 checksum;
>> > +     int eeprom_size;
>> > +     int result;
>> > +
>> > +     switch (priv->chip_type) {
>> > +     case FT232RL:
>> > +             eeprom_size = 0x40;
>> > +             break;
>> > +     default:
>> > +             /* Unsupported for brick repair */
>> > +             return 0;
>> > +     }
>> > +
>> > +     /* Latency timer needs to be 0x77 to unlock EEPROM
>programming */
>> > +     if (priv->latency != 0x77) {
>> > +             orig_latency = priv->latency;
>> > +             priv->latency = 0x77;
>> > +             rv = write_latency_timer(port);
>> > +             priv->latency = orig_latency;
>> > +             if (rv < 0)
>> > +                     return -EIO;
>> > +     }
>>
>> Do you really want to change this without returning to the original?
>> @@ -2255,6 +2364,12 @@ static int ftdi_sio_port_probe(struct
>usb_serial_port *port)
>>         ftdi_set_max_packet_size(port);
>>         if (read_latency_timer(port) < 0)
>>                 priv->latency = 16;
>> +       vendor_id =
>le16_to_cpu(port->serial->dev->descriptor.idVendor);
>> +       product_id =
>le16_to_cpu(port->serial->dev->descriptor.idProduct);
>> +       if (vendor_id == FTDI_VID &&
>> +               product_id == FTDI_BRICK_PID &&
>> +               priv->chip_type == FT232RL)
>> +               ftdi_repair_brick(port);
>>         write_latency_timer(port);
>It should get restored here.
>>         create_sysfs_attrs(port);
>>
>>
>>         Regards
>>                 Oliver
>>

-- 
Hector Martin "marcan" (hector@marcansoft.com)
Public key: https://mrcn.st/pub