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Date: Thu, 24 Aug 2023 13:32:57 -0500 From: Andrew Halaney <ahalaney@...hat.com> To: Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Maxime Coquelin <mcoquelin.stm32@...il.com>, Richard Cochran <richardcochran@...il.com> Cc: netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Andrew Halaney <ahalaney@...hat.com> Subject: [PATCH net-next 6/7] net: stmmac: Fix comment about default addend calculation The comment neglects that freq_div_ratio is the ratio between the subsecond increment frequency and the clk_ptp_rate frequency. Signed-off-by: Andrew Halaney <ahalaney@...hat.com> --- drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index dfead0df6163..64185753865f 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -853,10 +853,12 @@ int stmmac_init_tstamp_counter(struct stmmac_priv *priv, u32 systime_flags) /* Store sub second increment for later use */ priv->sub_second_inc = sub_second_inc; - /* calculate default addend value: - * formula is : - * addend = (2^32)/freq_div_ratio; - * where, freq_div_ratio = 1e9ns/sub_second_inc + /* Calculate default addend so the accumulator overflows (2^32) in + * sub_second_inc (ns). The addend is added to the accumulator + * every clk_ptp cycle. + * + * addend = (2^32) / freq_div_ratio + * where, freq_div_ratio = (1e9ns / sub_second_inc) / clk_ptp_rate */ temp = div_u64(NSEC_PER_SEC, sub_second_inc); temp = temp << 32; -- 2.41.0
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