• Maciej W. Rozycki's avatar
    serial: Z85C30: avoid a hang at console switch-over · 37713591
    Maciej W. Rozycki authored
    Changes to the generic console support code that happened a while ago
    introduced a scenario where the initial console is used in parallel with
    the final console during a brief period when switching between the two is
    in progress.  During that time a message about the switch-over is printed.
    
    With some combinations of chips, firmware and drivers, such as the Zilog
    Z85C30 SCC used with the DECstation, a hang may happen because the
    firmware used for the initial console may not expect the state of the chip
    after it has been initialised by the driver.  This is not a bug in the
    firmware, as some registers it would have to examine are write-only.
    
    This is a workaround for the Z85C30 which reuses the power-management
    callback to keep the transmitter of the line associated with the console
    enabled.  It reflects the consensus reached in a discussion a while ago.
    Signed-off-by: default avatarMaciej W. Rozycki <macro@linux-mips.org>
    Cc: Jiri Slaby <jirislaby@gmail.com>
    Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    37713591
zs.c 30.5 KB