linux-kernel - [PATCH 4.14 050/183] net: stmmac: dwmac-meson8b: fix setting the RGMII TX clock on Meson8b

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Message-Id: <20180425103244.567375102@linuxfoundation.org>
Date:   Wed, 25 Apr 2018 12:34:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Emiliano Ingrassia <ingrassia@...genesys.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.14 050/183] net: stmmac: dwmac-meson8b: fix setting the RGMII TX clock on Meson8b

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Blumenstingl <martin.blumenstingl@...glemail.com>


[ Upstream commit 433c6cab9d298687c097f6ee82e49157044dc7c6 ]

Meson8b only supports MPLL2 as clock input. The rate of the MPLL2 clock
set by Odroid-C1's u-boot is close to (but not exactly) 500MHz. The
exact rate is 500002394Hz, which is calculated in
drivers/clk/meson/clk-mpll.c using the following formula:
DIV_ROUND_UP_ULL((u64)parent_rate * SDM_DEN, (SDM_DEN * n2) + sdm)
Odroid-C1's u-boot configures MPLL2 with the following values:
- SDM_DEN = 16384
- SDM = 1638
- N2 = 5

The 250MHz clock (m250_div) inside dwmac-meson8b driver is derived from
the MPLL2 clock. Due to MPLL2 running slightly faster than 500MHz the
common clock framework chooses a divider which is too big to generate
the 250MHz clock (a divider of 2 would be needed, but this is rounded up
to a divider of 3). This breaks the RTL8211F RGMII PHY on Odroid-C1
because it requires a (close to) 125MHz RGMII TX clock (on Gbit speeds,
the IP block internally divides that down to 25MHz on 100Mbit/s
connections and 2.5MHz on 10Mbit/s connections - we don't need any
special configuration for that).

Round the divider to the closest value to prevent this issue on Meson8b.
This means we'll now end up with a clock rate for the RGMII TX clock of
125001197Hz (= 125MHz plus 1197Hz), which is close-enough to 125MHz.
This has no effect on the Meson GX SoCs since there fclk_div2 is used as
input clock, which has a rate of 1000MHz (and thus is divisible cleanly
to 250MHz and 125MHz).

Fixes: 566e8251625304 ("net: stmmac: add a glue driver for the Amlogic Meson 8b / GXBB DWMAC")
Reported-by: Emiliano Ingrassia <ingrassia@...genesys.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Reviewed-by: Jerome Brunet <jbrunet@...libre.com>
Tested-by: Jerome Brunet <jbrunet@...libre.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
@@ -144,7 +144,9 @@ static int meson8b_init_clk(struct meson
 	dwmac->m250_div.shift = PRG_ETH0_CLK_M250_DIV_SHIFT;
 	dwmac->m250_div.width = PRG_ETH0_CLK_M250_DIV_WIDTH;
 	dwmac->m250_div.hw.init = &init;
-	dwmac->m250_div.flags = CLK_DIVIDER_ONE_BASED | CLK_DIVIDER_ALLOW_ZERO;
+	dwmac->m250_div.flags = CLK_DIVIDER_ONE_BASED |
+				CLK_DIVIDER_ALLOW_ZERO |
+				CLK_DIVIDER_ROUND_CLOSEST;
 
 	dwmac->m250_div_clk = devm_clk_register(dev, &dwmac->m250_div.hw);
 	if (WARN_ON(IS_ERR(dwmac->m250_div_clk)))