net: stmmac: Calculate CDC error only once
The clock domain crossing error (CDC) is calculated at every fetch of Tx or Rx timestamps. It includes a division. Especially on arm32 based systems it is expensive. It also requires two conditionals in the hotpath. Add a compensation value cache to struct plat_stmmacenet_data and subtract it unconditionally in the RX/TX functions which spares the conditionals. The value is initialized to 0 and if supported calculated in the PTP initialization code. Suggested-by:Thomas Gleixner <tglx@linutronix.de> Signed-off-by:
Kurt Kanzenbach <kurt@linutronix.de> Link: https://lore.kernel.org/r/20211122111931.135135-1-kurt@linutronix.de Signed-off-by:
Jakub Kicinski <kuba@kernel.org>
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