• Stefan Agner's avatar
    ARM: dts: vf610: use reset values for L2 cache latencies · 9c171905
    Stefan Agner authored
    Linux on Vybrid used several different L2 latencies so far, none
    of them seem to be the right ones. According to the application note
    AN4947 ("Understanding Vybrid Architecture"), the tag portion runs
    on CPU clock and is inside the L2 cache controller, whereas the data
    portion is stored in the external SRAM running on platform clock.
    Hence it is likely that the correct value requires a higher data
    latency then tag latency.
    
    These are the values which have been used so far:
    - The mainline values:
      arm,data-latency = <1 1 1>;
      arm,tag-latency = <2 2 2>;
      Those values have lead to problems on higher clocks. They look
      like a poor translation from the reset values (missing +1 offset
      and a mix up between tag/latency values).
    - The Linux 3.0 (SoC vendor BSP) values (converted to DT notation):
      arm,data-latency = <4 2 3>
      arm,tag-latency = <4 2 3>
      The cache initialization function along with the value matches the
      i.MX6 code from the same kernel, so it seems that those values have
      just been copied.
    - The Colibri values:
      arm,data-latency = <2 1 2>;
      arm,tag-latency = <3 2 3>;
      Those were a mix between the values of the Linux 3.0 based BSP and
      the mainline values above.
    - The SoC Reset values (converted to DT notation):
      arm,data-latency = <3 3 3>;
      arm,tag-latency = <2 2 2>;
    
    So far there is no official statement on what the correct values are.
    See also the related Freescale community thread:
    https://community.freescale.com/message/579785#579785
    
    For now, the reset values seem to be the best bet. Remove all other
    "bogus" values and use the reset value on vf610.dtsi level.
    Signed-off-by: default avatarStefan Agner <stefan@agner.ch>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarShawn Guo <shawnguo@kernel.org>
    9c171905
vf610-colibri.dtsi 491 Bytes