can: rockchip_canfd: rkcanfd_register_done(): add warning for erratum 5

Tests on the rk3568v2 and rk3568v3 show that a reduced "baudclk" (e.g.
80MHz, compared to the standard 300MHz) significantly increases the
possibility of incorrect FIFO counters, i.e. erratum 5.

Print an info message if the clock is below the known good value of
300MHz.
Tested-by: Alibek Omarov <a1ba.omarov@gmail.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patch.msgid.link/20240904-rockchip-canfd-v5-10-8ae22bcb27cc@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/rockchip/rockchip_canfd-core.c

@@ -738,6 +738,13 @@ static void rkcanfd_register_done(const struct rkcanfd_priv *priv)
 		    FIELD_GET(RKCANFD_REG_RTL_VERSION_MAJOR, dev_id),
 		    FIELD_GET(RKCANFD_REG_RTL_VERSION_MINOR, dev_id),
 		    priv->devtype_data.quirks);
+
+	if (priv->devtype_data.quirks & RKCANFD_QUIRK_RK3568_ERRATUM_5 &&
+	    priv->can.clock.freq < RKCANFD_ERRATUM_5_SYSCLOCK_HZ_MIN)
+		netdev_info(priv->ndev,
+			    "Erratum 5: CAN clock frequency (%luMHz) lower than known good (%luMHz), expect degraded performance\n",
+			    priv->can.clock.freq / MEGA,
+			    RKCANFD_ERRATUM_5_SYSCLOCK_HZ_MIN / MEGA);
 }
 
 static int rkcanfd_register(struct rkcanfd_priv *priv)