r8169: deprecate support for RTL_GIGA_MAC_VER_27

RTL8168dp is ancient anyway, and I haven't seen any trace of its early
version 27 yet. This chip versions needs quite some special handling,
therefore it would facilitate driver maintenance if support for it
could be dropped. For now just disable detection of this chip version.
If nobody complains we can remove support for it in the near future.

v2:
- extend unknown chip version error message

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/ca98f018-a0e1-8762-e95c-f0ad773a0271@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/realtek/r8169_main.c

@@ -1981,7 +1981,11 @@ static enum mac_version rtl8169_get_mac_version(u16 xid, bool gmii)
 		{ 0x7c8, 0x280,	RTL_GIGA_MAC_VER_26 },
 
 		/* 8168DP family. */
-		{ 0x7cf, 0x288,	RTL_GIGA_MAC_VER_27 },
+		/* It seems this early RTL8168dp version never made it to
+		 * the wild. Let's see whether somebody complains, if not
+		 * we'll remove support for this chip version completely.
+		 * { 0x7cf, 0x288,      RTL_GIGA_MAC_VER_27 },
+		 */
 		{ 0x7cf, 0x28a,	RTL_GIGA_MAC_VER_28 },
 		{ 0x7cf, 0x28b,	RTL_GIGA_MAC_VER_31 },
 
@@ -5264,7 +5268,7 @@ static int rtl_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 	/* Identify chip attached to board */
 	chipset = rtl8169_get_mac_version(xid, tp->supports_gmii);
 	if (chipset == RTL_GIGA_MAC_NONE) {
-		dev_err(&pdev->dev, "unknown chip XID %03x\n", xid);
+		dev_err(&pdev->dev, "unknown chip XID %03x, contact r8169 maintainers (see MAINTAINERS file)\n", xid);
 		return -ENODEV;
 	}