[PATCH v2] net: zynq_gem: Wait for SGMII PCS link in zynq_gem_init()

[Stefan Roese]

In our system using ZynqMP with an external SGMII PHY it's necessary
to wait for the PCS link and auto negotiation to finish before the xfer
starts. Otherwise the first packet(s) might get dropped, resulting in a
delay at the start of the ethernet transfers.

This is only done when the PHY link is already up, which is done in
phy_startup(). As waiting for the PHY link bits via pcsstatus does not
make much sense, when the link is not available in general (e.g. no
cable connected).

This patch adds the necessary code including a minimal delay of 1 ms
which fixes problems of dropped first packages.

Signed-off-by: Stefan Roese <sr at denx.de>
Cc: Michal Simek <michal.simek at amd.com>
Cc: Katakam Harini <harini.katakam at amd.com>
Cc: Ramon Fried <rfried.dev at gmail.com>
Cc: Sean Anderson <sean.anderson at seco.com>
---
v2:
- Move wait for PCS link into the code path only executed for SGMII w/o
  fixed-link
- Reduce additional delay from 10 to 1ms
- Change dev_err to dev_warn

 drivers/net/zynq_gem.c | 36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/drivers/net/zynq_gem.c b/drivers/net/zynq_gem.c
index 507b19b75975..26565d78dafd 100644
--- a/drivers/net/zynq_gem.c
+++ b/drivers/net/zynq_gem.c
@@ -125,6 +125,10 @@
  */
 #define PHY_DETECT_MASK 0x1808
 
+/* PCS (SGMII) Link Status */
+#define ZYNQ_GEM_PCSSTATUS_LINK		BIT(2)
+#define ZYNQ_GEM_PCSSTATUS_ANEG_COMPL	BIT(5)
+
 /* TX BD status masks */
 #define ZYNQ_GEM_TXBUF_FRMLEN_MASK	0x000007ff
 #define ZYNQ_GEM_TXBUF_EXHAUSTED	0x08000000
@@ -164,7 +168,8 @@ struct zynq_gem_regs {
 	u32 stat[STAT_SIZE]; /* 0x100 - Octects transmitted Low reg */
 	u32 reserved9[20];
 	u32 pcscntrl;
-	u32 rserved12[36];
+	u32 pcsstatus;
+	u32 rserved12[35];
 	u32 dcfg6; /* 0x294 Design config reg6 */
 	u32 reserved7[106];
 	u32 transmit_q1_ptr; /* 0x440 - Transmit priority queue 1 */
@@ -491,12 +496,37 @@ static int zynq_gem_init(struct udevice *dev)
 		 * Must be written after PCS_SEL is set in nwconfig,
 		 * otherwise writes will not take effect.
 		 */
-		if (priv->phydev->phy_id != PHY_FIXED_ID)
+		if (priv->phydev->phy_id != PHY_FIXED_ID) {
 			writel(readl(&regs->pcscntrl) | ZYNQ_GEM_PCS_CTL_ANEG_ENBL,
 			       &regs->pcscntrl);
-		else
+			/*
+			 * When the PHY link is already up, the PCS link needs
+			 * to get re-checked
+			 */
+			if (priv->phydev->link) {
+				u32 pcsstatus;
+
+				pcsstatus = ZYNQ_GEM_PCSSTATUS_LINK |
+					ZYNQ_GEM_PCSSTATUS_ANEG_COMPL;
+				ret = wait_for_bit_le32(&regs->pcsstatus,
+							pcsstatus,
+							true, 5000, true);
+				if (ret) {
+					dev_warn(dev,
+						 "no PCS (SGMII) link\n");
+				} else {
+					/*
+					 * Some additional minimal delay seems
+					 * to be needed so that the first
+					 * packet will be sent correctly
+					 */
+					mdelay(1);
+				}
+			}
+		} else {
 			writel(readl(&regs->pcscntrl) & ~ZYNQ_GEM_PCS_CTL_ANEG_ENBL,
 			       &regs->pcscntrl);
+		}
 	}
 #endif
 
-- 
2.39.1