• Luis R. Rodriguez's avatar
    ath9k: Fix maximum tx fifo settings for single stream devices · f4709fdf
    Luis R. Rodriguez authored
    Atheros single stream AR9285 and AR9271 have half the PCU TX FIFO
    buffer size of that of dual stream devices. Dual stream devices
    have a max PCU TX FIFO size of 8 KB while single stream devices
    have 4 KB. Single stream devices have an issue though and require
    hardware only to use half of the amount of its capable PCU TX FIFO
    size, 2 KB and this requires a change in software.
    
    Technically a change would not have been required (except for frame
    burst considerations of 128 bytes) if these devices would have been
    able to use the full 4 KB of the PCU TX FIFO size but our systems
    engineers recommend 2 KB to be used only. We enforce this through
    software by reducing the max frame triggger level to 2 KB.
    
    Fixing the max frame trigger level should then have a few benefits:
    
      * The PER will now be adjusted as designed for underruns when the
        max trigger level is reached. This should help alleviate the
        bus as the rate control algorithm chooses a slower rate which
        should ensure frames are transmitted properly under high system
        bus load.
    
      * The poll we use on our TX queues should now trigger and work
        as designed for single stream devices. The hardware passes
        data from each TX queue on the PCU TX FIFO queue respecting each
        queue's priority. The new trigger level ensures this seeding of
        the PCU TX FIFO queue occurs as designed which could mean avoiding
        false resets and actually reseting hw correctly when a TX queue
        is indeed stuck.
    
      * Some undocumented / unsupported behaviour could have been triggered
        when the max trigger level level was being set to 4 KB on single
        stream devices. Its not clear what this issue was to me yet.
    
    Cc: Kyungwan Nam <kyungwan.nam@atheros.com>
    Cc: Bennyam Malavazi <bennyam.malavazi@atheros.com>
    Cc: Stephen Chen <stephen.chen@atheros.com>
    Cc: Shan Palanisamy <shan.palanisamy@atheros.com>
    Cc: Paul Shaw <paul.shaw@atheros.com>
    Signed-off-by: default avatarVasanthakumar Thiagarajan <vasanth@atheros.com>
    Signed-off-by: default avatarLuis R. Rodriguez <lrodriguez@atheros.com>
    Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
    f4709fdf
rc.c 43.5 KB