• Marek Vasut's avatar
    net: stmmac: Initialize MAC_ONEUS_TIC_COUNTER register · 8efbdbfa
    Marek Vasut authored
    Initialize MAC_ONEUS_TIC_COUNTER register with correct value derived
    from CSR clock, otherwise EEE is unstable on at least NXP i.MX8M Plus
    and Micrel KSZ9131RNX PHY, to the point where not even ARP request can
    be sent out.
    
    i.MX 8M Plus Applications Processor Reference Manual, Rev. 1, 06/2021
    11.7.6.1.34 One-microsecond Reference Timer (MAC_ONEUS_TIC_COUNTER)
    defines this register as:
    "
    This register controls the generation of the Reference time (1 microsecond
    tic) for all the LPI timers. This timer has to be programmed by the software
    initially.
    ...
    The application must program this counter so that the number of clock cycles
    of CSR clock is 1us. (Subtract 1 from the value before programming).
    For example if the CSR clock is 100MHz then this field needs to be programmed
    to value 100 - 1 = 99 (which is 0x63).
    This is required to generate the 1US events that are used to update some of
    the EEE related counters.
    "
    
    The reset value is 0x63 on i.MX8M Plus, which means expected CSR clock are
    100 MHz. However, the i.MX8M Plus "enet_qos_root_clk" are 266 MHz instead,
    which means the LPI timers reach their count much sooner on this platform.
    
    This is visible using a scope by monitoring e.g. exit from LPI mode on TX_CTL
    line from MAC to PHY. This should take 30us per STMMAC_DEFAULT_TWT_LS setting,
    during which the TX_CTL line transitions from tristate to low, and 30 us later
    from low to high. On i.MX8M Plus, this transition takes 11 us, which matches
    the 30us * 100/266 formula for misconfigured MAC_ONEUS_TIC_COUNTER register.
    
    Configure MAC_ONEUS_TIC_COUNTER based on CSR clock, so that the LPI timers
    have correct 1us reference. This then fixes EEE on i.MX8M Plus with Micrel
    KSZ9131RNX PHY.
    
    Fixes: 477286b5 ("stmmac: add GMAC4 core support")
    Signed-off-by: default avatarMarek Vasut <marex@denx.de>
    Tested-by: default avatarHarald Seiler <hws@denx.de>
    Reviewed-by: default avatarFrancesco Dolcini <francesco.dolcini@toradex.com>
    Tested-by: Francesco Dolcini <francesco.dolcini@toradex.com> # Toradex Verdin iMX8MP
    Reviewed-by: default avatarJesse Brandeburg <jesse.brandeburg@intel.com>
    Link: https://lore.kernel.org/r/20230506235845.246105-1-marex@denx.deSigned-off-by: default avatarJakub Kicinski <kuba@kernel.org>
    8efbdbfa
dwmac4.h 18.1 KB