net: phy: mscc-miim: read poll when high resolution timers are disabled

The driver uses a read polling mechanism to check the status of the MDIO
bus, to know if it is ready to accept next commands. This polling
mechanism uses usleep_delay() under the hood between reads which is fine
as long as high resolution timers are enabled. Otherwise the delays will
end up to be much longer than expected.

This patch fixes this by using udelay() under the hood when
CONFIG_HIGH_RES_TIMERS isn't enabled. This increases CPU usage.
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/Kconfig

@@ -184,7 +184,8 @@ config MDIO_MSCC_MIIM
 	depends on HAS_IOMEM
 	help
 	  This driver supports the MIIM (MDIO) interface found in the network
-	  switches of the Microsemi SoCs
+	  switches of the Microsemi SoCs; it is recommended to switch on
+	  CONFIG_HIGH_RES_TIMERS
 
 config MDIO_MVUSB
 	tristate "Marvell USB to MDIO Adapter"

drivers/net/phy/mdio-mscc-miim.c

@@ -39,13 +39,25 @@ struct mscc_miim_dev {
 	void __iomem *phy_regs;
 };
 
+/* When high resolution timers aren't built-in: we can't use usleep_range() as
+ * we would sleep way too long. Use udelay() instead.
+ */
+#define mscc_readl_poll_timeout(addr, val, cond, delay_us, timeout_us)	\
+({									\
+	if (!IS_ENABLED(CONFIG_HIGH_RES_TIMERS))			\
+		readl_poll_timeout_atomic(addr, val, cond, delay_us,	\
+					  timeout_us);			\
+	readl_poll_timeout(addr, val, cond, delay_us, timeout_us);	\
+})
+
 static int mscc_miim_wait_ready(struct mii_bus *bus)
 {
 	struct mscc_miim_dev *miim = bus->priv;
 	u32 val;
 
-	return readl_poll_timeout(miim->regs + MSCC_MIIM_REG_STATUS, val,
-				  !(val & MSCC_MIIM_STATUS_STAT_BUSY), 50, 10000);
+	return mscc_readl_poll_timeout(miim->regs + MSCC_MIIM_REG_STATUS, val,
+				       !(val & MSCC_MIIM_STATUS_STAT_BUSY), 50,
+				       10000);
 }
 
 static int mscc_miim_wait_pending(struct mii_bus *bus)
@@ -53,7 +65,7 @@ static int mscc_miim_wait_pending(struct mii_bus *bus)
 	struct mscc_miim_dev *miim = bus->priv;
 	u32 val;
 
-	return readl_poll_timeout(miim->regs + MSCC_MIIM_REG_STATUS, val,
+	return mscc_readl_poll_timeout(miim->regs + MSCC_MIIM_REG_STATUS, val,
 				       !(val & MSCC_MIIM_STATUS_STAT_PENDING),
 				       50, 10000);
 }