net: stmmac: allow CSR clock of 300MHz

[ Upstream commit 08dad2f4d541fcfe5e7bfda72cc6314bbfd2802f ]

The Synopsys Ethernet IP uses the CSR clock as a base clock for MDC.
The divisor used is set in the MAC_MDIO_Address register field CR
(Clock Rate)

The divisor is there to change the CSR clock into a clock that falls
below the IEEE 802.3 specified max frequency of 2.5MHz.

If the CSR clock is 300MHz, the code falls back to using the reset
value in the MAC_MDIO_Address register, as described in the comment
above this code.

However, 300MHz is actually an allowed value and the proper divider
can be estimated quite easily (it's just 1Hz difference!)

A CSR frequency of 300MHz with the maximum clock rate value of 0x5
(STMMAC_CSR_250_300M, a divisor of 124) gives somewhere around
~2.42MHz which is below the IEEE 802.3 specified maximum.

For the ARTPEC-8 SoC, the CSR clock is this problematic 300MHz,
and unfortunately, the reset-value of the MAC_MDIO_Address CR field
is 0x0.

This leads to a clock rate of zero and a divisor of 42, and gives an
MDC frequency of ~7.14MHz.

Allow CSR clock of 300MHz by making the comparison inclusive.

Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index dbd56fefa2f3f7202018c10bb1b6741d6cf50a03..0a7ff854d1c34528db7f6c91d0d970a5e97a29e1 100644 (file)
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -178,7 +178,7 @@ static void stmmac_clk_csr_set(struct stmmac_priv *priv)
                        priv->clk_csr = STMMAC_CSR_100_150M;
                else if ((clk_rate >= CSR_F_150M) && (clk_rate < CSR_F_250M))
                        priv->clk_csr = STMMAC_CSR_150_250M;
-               else if ((clk_rate >= CSR_F_250M) && (clk_rate < CSR_F_300M))
+               else if ((clk_rate >= CSR_F_250M) && (clk_rate <= CSR_F_300M))
                        priv->clk_csr = STMMAC_CSR_250_300M;
        }
 }