tools/linux.py: Speed u-boot boot up

Drop 'preboot' env variable and set bootdelay to 0. When booting via
u-boot there is no need to start USB via the preboot command. Probing
all USB ports takes u-boot quite a while. It is not needed when booting
kernel and initramfs from memory.

Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

proxyclient/tools/linux.py

@@ -94,6 +94,8 @@
     bootenv = list(filter(lambda x: not (
         x.startswith("baudrate") or
         x.startswith("boot_") or
+        x.startswith("bootdelay=") or
+        x.startswith("preboot=") or
         x.startswith("bootcmd")
         ), bootenv))
 
@@ -109,6 +111,7 @@
     if tty_dev is not None:
         bootenv.append("baudrate=%d" % tty_dev.baudrate)
     bootenv.append(bootcmd)
+    bootenv.append("bootdelay=0")
     if args.bootargs is not None:
         bootenv.append("bootargs=" + args.bootargs)