ch347_spi: Add simple `spispeed` parameter

Add a programmer parameter `spispeed` that accepts a frequency in kHz
like it's done for other drivers. The frequency will be rounded down
to the closest possible divisor setting.

Change-Id: Ifa05b95f723dba81bdcc7015dcdf557af5f2e0a8
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/73153
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nicholas Chin <nic.c3.14@gmail.com>
diff --git a/flashrom.8.tmpl b/flashrom.8.tmpl
index fd5fc2a..3536e66 100644
--- a/flashrom.8.tmpl
+++ b/flashrom.8.tmpl
@@ -1245,8 +1245,23 @@
 used as per the device.
 .SS
 .BR "ch347_spi " programmer
-The WCH CH347 programmer does not currently support any parameters. SPI frequency is fixed at 2 MHz, and CS0 is
-used as per the device.
+.IP
+The driver is currently hard-coded to use
+.BR CS0 .
+An optional
+.B spispeed
+parameter specifies the frequency of the SPI bus.
+Syntax is
+.sp
+.B "  flashrom \-p ch347_spi:spispeed=frequency"
+.sp
+where
+.B frequency
+is given in
+.B kHz
+and can be in the range 468 .. 60000. The frequency will be rounded down to
+a supported value (60 MHz divided by a power of 2). The default is a frequency
+of 7.5 MHz.
 .SS
 .BR "ni845x_spi " programmer
 .IP