octeontx2-af: CN10KB: Fix FIFO length calculation for RPM2

RPM0 and RPM1 on the CN10KB SoC have 8 LMACs each, whereas RPM2
has only 4 LMACs. Similarly, the RPM0 and RPM1 have 256KB FIFO,
whereas RPM2 has 128KB FIFO. This patch fixes an issue with
improper TX credit programming for the RPM2 link.

Fixes: b9d0fed ("octeontx2-af: cn10kb: Add RPM_USX MAC support")
Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
Signed-off-by: Naveen Mamindlapalli <naveenm@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240108073036.8766-1-naveenm@marvell.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: nithind1988

drivers/net/ethernet/marvell/octeontx2/af/rpm.c

@@ -506,14 +506,19 @@ u32 rpm2_get_lmac_fifo_len(void *rpmd, int lmac_id)
 	rpm_t *rpm = rpmd;
 	u8 num_lmacs;
 	u32 fifo_len;
+	u16 max_lmac;
 
 	lmac_info = rpm_read(rpm, 0, RPM2_CMRX_RX_LMACS);
 	/* LMACs are divided into two groups and each group
 	 * gets half of the FIFO
 	 * Group0 lmac_id range {0..3}
 	 * Group1 lmac_id range {4..7}
 	 */
-	fifo_len = rpm->mac_ops->fifo_len / 2;
+	max_lmac = (rpm_read(rpm, 0, CGX_CONST) >> 24) & 0xFF;
+	if (max_lmac > 4)
+		fifo_len = rpm->mac_ops->fifo_len / 2;
+	else
+		fifo_len = rpm->mac_ops->fifo_len;
 
 	if (lmac_id < 4) {
 		num_lmacs = hweight8(lmac_info & 0xF);