mdio: Add 10GBASE-T SNR register definition

These do not have an in-kernel user but may be useful to user-space.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/mdio.h

@@ -46,6 +46,8 @@
 
 /* Media-dependent registers. */
 #define MDIO_PMA_10GBT_TXPWR	131	/* 10GBASE-T TX power control */
+#define MDIO_PMA_10GBT_SNR	133	/* 10GBASE-T SNR margin, lane A.
+					 * Lanes B-D are numbered 134-136. */
 #define MDIO_PMA_10GBR_FECABLE	170	/* 10GBASE-R FEC ability */
 #define MDIO_PCS_10GBX_STAT1	24	/* 10GBASE-X PCS status 1 */
 #define MDIO_PCS_10GBRT_STAT1	32	/* 10GBASE-R/-T PCS status 1 */
@@ -188,6 +190,11 @@
 /* PMA 10GBASE-T TX power register. */
 #define MDIO_PMA_10GBT_TXPWR_SHORT	0x0001	/* Short-reach mode */
 
+/* PMA 10GBASE-T SNR registers. */
+/* Value is SNR margin in dB, clamped to range [-127, 127], plus 0x8000. */
+#define MDIO_PMA_10GBT_SNR_BIAS		0x8000
+#define MDIO_PMA_10GBT_SNR_MAX		127
+
 /* PMA 10GBASE-R FEC ability register. */
 #define MDIO_PMA_10GBR_FECABLE_ABLE	0x0001	/* FEC ability */
 #define MDIO_PMA_10GBR_FECABLE_ERRABLE	0x0002	/* FEC error indic. ability */