• Bernd Edlinger's avatar
    net: stmmac: Wait a bit for the reset to take effect · a5f5eee2
    Bernd Edlinger authored
    otherwise the synopsys_id value may be read out wrong,
    because the GMAC_VERSION register might still be in reset
    state, for at least 1 us after the reset is de-asserted.
    
    Add a wait for 10 us before continuing to be on the safe side.
    
    > From what have you got that delay value?
    
    Just try and error, with very old linux versions and old gcc versions
    the synopsys_id was read out correctly most of the time (but not always),
    with recent linux versions and recnet gcc versions it was read out
    wrongly most of the time, but again not always.
    I don't have access to the VHDL code in question, so I cannot
    tell why it takes so long to get the correct values, I also do not
    have more than a few hardware samples, so I cannot tell how long
    this timeout must be in worst case.
    Experimentally I can tell that the register is read several times
    as zero immediately after the reset is de-asserted, also adding several
    no-ops is not enough, adding a printk is enough, also udelay(1) seems to
    be enough but I tried that not very often, and I have not access to many
    hardware samples to be 100% sure about the necessary delay.
    And since the udelay here is only executed once per device instance,
    it seems acceptable to delay the boot for 10 us.
    
    BTW: my hardware's synopsys id is 0x37.
    
    Fixes: c5e4ddbd ("net: stmmac: Add support for optional reset control")
    Signed-off-by: default avatarBernd Edlinger <bernd.edlinger@hotmail.de>
    Reviewed-by: default avatarJiri Pirko <jiri@nvidia.com>
    Reviewed-by: default avatarSerge Semin <fancer.lancer@gmail.com>
    Link: https://lore.kernel.org/r/AS8P193MB1285A810BD78C111E7F6AA34E4752@AS8P193MB1285.EURP193.PROD.OUTLOOK.COMSigned-off-by: default avatarJakub Kicinski <kuba@kernel.org>
    a5f5eee2
stmmac_main.c 219 KB