linux-kernel - stmmac: GMAC_RGSMIIIS reports bogus values

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Message-ID: <1478189833.4072.65.camel@synopsys.com>
Date:   Thu, 3 Nov 2016 16:17:56 +0000
From:   Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "manabian@...il.com" <manabian@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "fabrice.gasnier@...com" <fabrice.gasnier@...com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "alexandre.torgue@...il.com" <alexandre.torgue@...il.com>,
        "preid@...ctromag.com.au" <preid@...ctromag.com.au>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: stmmac: GMAC_RGSMIIIS reports bogus values

Hello,

I'm seeing pretty strange issue with GMAC reporting a lot of link state changes
based on bits in GMAC_RGSMIIIS. It looks like that:
-------------------------->8-----------------------
Link is Down
Link is Up - 10/Full
Link is Down
Link is Up - 10/Half
Link is Down
Link is Down
Link is Up - 10/Half
Link is Up -
1000/Half
Link is Down
Link is Down
Link is Down
Link is Down
Link is Up - 10/Half
Link is Down
Link is Down
Link is Up -
1000/Half
Link is Up - 1000/Full
-------------------------->8-----------------------

What's especially interesting my board with GMAC is connected to 100Mbit device
which means there's no chance for 1Gb mode to be set.

Also this has nothing to do with link state detected and reported by PHY via MDIO.
So obviously GMAC_RGSMIIIS bits are wrong. But given the fact that GMAC_RGSMIIIS bits
are set based on state of RXD[3:0] lines of RGMII I may only thing that it's
PHY (in my case DP83865) who's sending random data on the RXD during inter-frame gap.

Note data transferred through that networking connection is perfectly correct and
actually I haven't see those link state prints before kernel v4.8 basically
because the prints in question were implemented with pr_debug() and then with [1]
we got pr_info() that made prints visible by default.

Since I don't have any means to capture all required GMII signals to do better
analysis and my data is not corrupted in the end I'm thinking about way how to
mute these pretty senseless messages.

One thing I may think of we may disable checking of GMAC_RGSMIIIS if a particular
board uses MDIO for PHY setup. Something like that:
-------------------------->8-----------------------
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
@@ -337,7 +337,7 @@ static int dwmac1000_irq_status(struct mac_device_info *hw,
 
        dwmac_pcs_isr(ioaddr, GMAC_PCS_BASE, intr_status, x);
 
-       if (intr_status & PCS_RGSMIIIS_IRQ)
+       if (!priv->use_mdio && (intr_status & PCS_RGSMIIIS_IRQ))
                dwmac1000_rgsmii(ioaddr, x);
 
        return ret;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 6c85b61aaa0b..34e9de0450ba 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3356,11 +3356,13 @@ int stmmac_dvr_probe(struct device *device,
 
        stmmac_check_pcs_mode(priv);
 
+       priv->use_mdio = 0;
        if (priv->hw->pcs != STMMAC_PCS_RGMII  &&
            priv->hw->pcs != STMMAC_PCS_TBI &&
            priv->hw->pcs != STMMAC_PCS_RTBI) {
                /* MDIO bus Registration */
                ret = stmmac_mdio_register(ndev);
+               priv->use_mdio = 1;
                if (ret < 0) {
                        pr_debug("%s: MDIO bus (id: %d) registration failed",
                                 __func__, priv->plat->bus_id);
-------------------------->8-----------------------

Any thoughts on that are much appreciated!

Regards,
Alexey

[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=70523e639bf8ca09b3357371c3546cee55c06351