net: airoha: read default PSE reserved pages value before updating

Store the default value for the number of PSE reserved pages in orig_val
at the beginning of airoha_fe_set_pse_oq_rsv routine, before updating it
with airoha_fe_set_pse_queue_rsv_pages().
Introduce airoha_fe_get_pse_all_rsv utility routine.

Introduced by commit 23020f0 ("net: airoha: Introduce ethernet support
for EN7581 SoC")

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241001-airoha-eth-pse-fix-v2-1-9a56cdffd074@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/airoha_eth.c

@@ -1116,17 +1116,23 @@ static void airoha_fe_set_pse_queue_rsv_pages(struct airoha_eth *eth,
 		      PSE_CFG_WR_EN_MASK | PSE_CFG_OQRSV_SEL_MASK);
 }
 
+static u32 airoha_fe_get_pse_all_rsv(struct airoha_eth *eth)
+{
+	u32 val = airoha_fe_rr(eth, REG_FE_PSE_BUF_SET);
+
+	return FIELD_GET(PSE_ALLRSV_MASK, val);
+}
+
 static int airoha_fe_set_pse_oq_rsv(struct airoha_eth *eth,
 				    u32 port, u32 queue, u32 val)
 {
-	u32 orig_val, tmp, all_rsv, fq_limit;
+	u32 orig_val = airoha_fe_get_pse_queue_rsv_pages(eth, port, queue);
+	u32 tmp, all_rsv, fq_limit;
 
 	airoha_fe_set_pse_queue_rsv_pages(eth, port, queue, val);
 
 	/* modify all rsv */
-	orig_val = airoha_fe_get_pse_queue_rsv_pages(eth, port, queue);
-	tmp = airoha_fe_rr(eth, REG_FE_PSE_BUF_SET);
-	all_rsv = FIELD_GET(PSE_ALLRSV_MASK, tmp);
+	all_rsv = airoha_fe_get_pse_all_rsv(eth);
 	all_rsv += (val - orig_val);
 	airoha_fe_rmw(eth, REG_FE_PSE_BUF_SET, PSE_ALLRSV_MASK,
 		      FIELD_PREP(PSE_ALLRSV_MASK, all_rsv));