[PATCH net-next v4 10/14] net: dsa: b53: prevent BRCM_HDR access on older devices

["Álvaro Fernández Rojas" <noltari@gmail.com>]

Older switches don't implement BRCM_HDR register so we should avoid
reading or writing it.

Fixes: b409a9efa183 ("net: dsa: b53: Move Broadcom header setup to b53")
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
 drivers/net/dsa/b53/b53_common.c | 5 +++++
 1 file changed, 5 insertions(+)

 v4: no changes

 v3: add changes requested by Jonas:
  - Check for legacy tag protocols instead of is5325().

 v2: no changes

diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index daf7c1906711..2bcbb003b1fd 100644
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c
@@ -730,6 +730,11 @@ void b53_brcm_hdr_setup(struct dsa_switch *ds, int port)
 		hdr_ctl |= GC_FRM_MGMT_PORT_M;
 	b53_write8(dev, B53_MGMT_PAGE, B53_GLOBAL_CONFIG, hdr_ctl);
 
+	/* B53_BRCM_HDR not present on devices with legacy tags */
+	if (dev->tag_protocol == DSA_TAG_PROTO_BRCM_LEGACY ||
+	    dev->tag_protocol == DSA_TAG_PROTO_BRCM_LEGACY_FCS)
+		return;
+
 	/* Enable Broadcom tags for IMP port */
 	b53_read8(dev, B53_MGMT_PAGE, B53_BRCM_HDR, &hdr_ctl);
 	if (tag_en)
-- 
2.39.5