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Subject: Re: [RFC] net: phy: read link status twice when
 phy_check_link_status()
To:     liuyonglong <liuyonglong@huawei.com>, andrew@lunn.ch,
        davem@davemloft.net
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linuxarm@huawei.com, salil.mehta@huawei.com,
        yisen.zhuang@huawei.com, shiju.jose@huawei.com
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 <4b4ba599-f160-39e7-d611-45ac53268389@huawei.com>
 <a0b26e4b-e288-cf44-049a-7d0b7f5696eb@gmail.com>
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From:   Heiner Kallweit <hkallweit1@gmail.com>
Message-ID: <9a0a8094-42ee-0a18-0e9a-d3ca783d6d4b@gmail.com>
Date:   Tue, 30 Jul 2019 21:04:20 +0200
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On 30.07.2019 08:35, liuyonglong wrote:
> :/sys/kernel/debug/tracing$ cat trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 45/45   #P:128
> #
> #                              _-----=> irqs-off
> #                             / _----=> need-resched
> #                            | / _---=> hardirq/softirq
> #                            || / _--=> preempt-depth
> #                            ||| /     delay
> #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
> #              | |       |   ||||       |         |
>     kworker/64:2-1028  [064] ....   172.295687: mdio_access: mii-0000:bd:00.0 read  phy:0x01 reg:0x02 val:0x001c
>     kworker/64:2-1028  [064] ....   172.295726: mdio_access: mii-0000:bd:00.0 read  phy:0x01 reg:0x03 val:0xc916
>     kworker/64:2-1028  [064] ....   172.296902: mdio_access: mii-0000:bd:00.0 read  phy:0x01 reg:0x01 val:0x79ad
>     kworker/64:2-1028  [064] ....   172.296938: mdio_access: mii-0000:bd:00.0 read  phy:0x01 reg:0x0f val:0x2000
>     kworker/64:2-1028  [064] ....   172.321213: mdio_access: mii-0000:bd:00.0 read  phy:0x01 reg:0x00 val:0x1040
>     kworker/64:2-1028  [064] ....   172.343209: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x02 val:0x001c
>     kworker/64:2-1028  [064] ....   172.343245: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x03 val:0xc916
>     kworker/64:2-1028  [064] ....   172.343882: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x79ad
>     kworker/64:2-1028  [064] ....   172.343918: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x0f val:0x2000
>     kworker/64:2-1028  [064] ....   172.362658: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x00 val:0x1040
>     kworker/64:2-1028  [064] ....   172.385961: mdio_access: mii-0000:bd:00.2 read  phy:0x05 reg:0x02 val:0x001c
>     kworker/64:2-1028  [064] ....   172.385996: mdio_access: mii-0000:bd:00.2 read  phy:0x05 reg:0x03 val:0xc916
>     kworker/64:2-1028  [064] ....   172.386646: mdio_access: mii-0000:bd:00.2 read  phy:0x05 reg:0x01 val:0x79ad
>     kworker/64:2-1028  [064] ....   172.386681: mdio_access: mii-0000:bd:00.2 read  phy:0x05 reg:0x0f val:0x2000
>     kworker/64:2-1028  [064] ....   172.411286: mdio_access: mii-0000:bd:00.2 read  phy:0x05 reg:0x00 val:0x1040
>     kworker/64:2-1028  [064] ....   172.433225: mdio_access: mii-0000:bd:00.3 read  phy:0x07 reg:0x02 val:0x001c
>     kworker/64:2-1028  [064] ....   172.433260: mdio_access: mii-0000:bd:00.3 read  phy:0x07 reg:0x03 val:0xc916
>     kworker/64:2-1028  [064] ....   172.433887: mdio_access: mii-0000:bd:00.3 read  phy:0x07 reg:0x01 val:0x79ad
>     kworker/64:2-1028  [064] ....   172.433922: mdio_access: mii-0000:bd:00.3 read  phy:0x07 reg:0x0f val:0x2000
>     kworker/64:2-1028  [064] ....   172.452862: mdio_access: mii-0000:bd:00.3 read  phy:0x07 reg:0x00 val:0x1040
>         ifconfig-1324  [011] ....   177.325585: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x00 val:0x1040
>   kworker/u257:0-8     [012] ....   177.325642: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x04 val:0x01e1
>   kworker/u257:0-8     [012] ....   177.325654: mdio_access: mii-0000:bd:00.1 write phy:0x03 reg:0x04 val:0x05e1
>   kworker/u257:0-8     [012] ....   177.325708: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x79ad
>   kworker/u257:0-8     [012] ....   177.325744: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x09 val:0x0200
>   kworker/u257:0-8     [012] ....   177.325779: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x00 val:0x1040
>   kworker/u257:0-8     [012] ....   177.325788: mdio_access: mii-0000:bd:00.1 write phy:0x03 reg:0x00 val:0x1240
>   kworker/u257:0-8     [012] ....   177.325843: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x798d

What I think that happens here:
Writing 0x1240 to BMCR starts aneg. When reading BMSR immediately after that then the PHY seems to have cleared
the "aneg complete" bit already, but not yet the "link up" bit. This results in the false "link up" notification.
The following patch is based on the fact that in case of enabled aneg we can't have a valid link if aneg isn't
finished. Could you please test whether this works for you?

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 6b5cb87f3..7ddd91df9 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1774,6 +1774,12 @@ int genphy_update_link(struct phy_device *phydev)
 	phydev->link = status & BMSR_LSTATUS ? 1 : 0;
 	phydev->autoneg_complete = status & BMSR_ANEGCOMPLETE ? 1 : 0;
 
+	/* Consider the case that autoneg was started and "aneg complete"
+	 * bit has been reset, but "link up" bit not yet.
+	 */
+	if (phydev->autoneg == AUTONEG_ENABLE && !phydev->autoneg_complete)
+		phydev->link = 0;
+
 	return 0;
 }
 EXPORT_SYMBOL(genphy_update_link);
-- 
2.22.0


>   kworker/u257:0-8     [003] ....   178.360488: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x7989
>   kworker/u257:0-8     [000] ....   179.384479: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x7989
>   kworker/u257:0-8     [000] ....   180.408477: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x7989
>   kworker/u257:0-8     [000] ....   181.432474: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x79a9
>   kworker/u257:0-8     [000] ....   181.432510: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x0a val:0x7800
>   kworker/u257:0-8     [000] ....   181.432546: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x09 val:0x0200
>   kworker/u257:0-8     [000] ....   181.432582: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x05 val:0xc1e1
>   kworker/u257:0-8     [000] ....   182.456510: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x79ad
>   kworker/u257:0-8     [000] ....   182.456546: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x0a val:0x4800
>   kworker/u257:0-8     [000] ....   182.456582: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x09 val:0x0200
>   kworker/u257:0-8     [000] ....   182.456618: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x05 val:0xc1e1
>   kworker/u257:0-8     [001] ....   183.480476: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x79ad
>   kworker/u257:0-8     [000] ....   184.504478: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x79ad
>   kworker/u257:0-8     [000] ....   185.528486: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x79ad
>   kworker/u257:0-8     [000] ....   186.552475: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x01 val:0x79ad
>         ifconfig-1327  [011] ....   187.196036: mdio_access: mii-0000:bd:00.1 read  phy:0x03 reg:0x00 val:0x1040
>         ifconfig-1327  [011] ....   187.196046: mdio_access: mii-0000:bd:00.1 write phy:0x03 reg:0x00 val:0x1840
> 
> 
[...]
>>
>>>
>>>
>>>
>>
>> Heiner
>>
>> .
>>
> 
> .
>