On Thu, Sep 05, 2019 at 01:50:49PM -0500, Steve Maher wrote:
> I've been googling and perusing the source tree, but am still unsure if
> general bitbang support is present in flashrom.
> Specifically, I have a board which has an onboard FT2232H with some of the
> GPIO pins wired to a SPI flash device. The pins used are NOT the MPSSE SPI
> pins from the 2232, but rather some other unused GPIO pins (the MPSSE
> dedicated pins are being used for JTAG, and the other 2232 channel is being
> used for data transfer), and I can't change the wiring from the 2232 to the
> SPI flash.
You're talking about the CBUS pins?
> Does flashrom support this type of configuration? If there is general
> bitbang support, I can write the necessary routines to control the pins of
> the 2232 in a bitbang fashion.
This sounds exactly how the developerbox_spi.c driver works. In that case
the GPIO pins are hooked up to a CP2102N rather than an RT2232H but all
the principles should be the same.
Assuming the USB wire protocol is of the set pins/read pins variety
(each a seperate USB transation) then things can work but it is
extremely slow. Even after a bit of optimisation to make it easier to
coalesce USB packets then my notes mention read performance roughly on
par with a 2400 baud modem (between 60 and 70 minutes per megabyte if
you prefer) and write performance was 50% slower still!
> Any pointers here would be much appreciated.
How do you hope to toggle the pins? Using libgpiod (e.g. use kernel-side
FTDI driver and use the GPIO user/kernel interface) or via libftdi (e.g.
userspace FTDI driver that uses the raw USB user/kernel interface).
libgpiod is more generic but I think libftdi would be faster because it
would be easier to coalesce USB packets.
If you want to go via libftdi then perhaps try starting from the
developerbox_spi.c driver, rip out the CP210XN code and replace it
with libftdi calls to manipulate the CBUS pins. See
for inspiration on that.