net: stmmac: Apply redundant write work around on 4.xx too

commit a3a57bf ("net: stmmac: work
around sporadic tx issue on link-up") worked around a problem with TX
sometimes not working after a link-up by avoiding a redundant write to
MAC_CTRL_REG (aka GMAC_CONFIG), since the IP appeared to have problems
with handling multiple writes to that register in some cases.

That commit however only added the work around to dwmac_lib.c (apart
from the common code in stmmac_main.c), but my systems with version
4.21a of the IP exhibit the same problem, so add the work around to
dwmac4_lib.c too.

Fixes: a3a57bf ("net: stmmac: work around sporadic tx issue on link-up")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230721-stmmac-tx-workaround-v1-1-9411cbd5ee07@axis.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: vwax

drivers/net/ethernet/stmicro/stmmac/dwmac4_lib.c

@@ -240,13 +240,15 @@ void stmmac_dwmac4_set_mac_addr(void __iomem *ioaddr, const u8 addr[6],
 void stmmac_dwmac4_set_mac(void __iomem *ioaddr, bool enable)
 {
 	u32 value = readl(ioaddr + GMAC_CONFIG);
+	u32 old_val = value;
 
 	if (enable)
 		value |= GMAC_CONFIG_RE | GMAC_CONFIG_TE;
 	else
 		value &= ~(GMAC_CONFIG_TE | GMAC_CONFIG_RE);
 
-	writel(value, ioaddr + GMAC_CONFIG);
+	if (value != old_val)
+		writel(value, ioaddr + GMAC_CONFIG);
 }
 
 void stmmac_dwmac4_get_mac_addr(void __iomem *ioaddr, unsigned char *addr,