linux-kernel - Re: [PATCH net v1] net: phy: smsc: fix printing too many logs

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Date:   Thu, 18 Jun 2020 01:50:39 +0800
From:   Dejin Zheng <zhengdejin5@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     f.fainelli@...il.com, hkallweit1@...il.com, linux@...linux.org.uk,
        davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Kevin Groeneveld <kgroeneveld@...il.com>
Subject: Re: [PATCH net v1] net: phy: smsc: fix printing too many logs

On Wed, Jun 17, 2020 at 06:19:25PM +0200, Andrew Lunn wrote:
> On Wed, Jun 17, 2020 at 11:33:40PM +0800, Dejin Zheng wrote:
> > Commit 7ae7ad2f11ef47 ("net: phy: smsc: use phy_read_poll_timeout()
> > to simplify the code") will print a lot of logs as follows when Ethernet
> > cable is not connected:
> > 
> > [    4.473105] SMSC LAN8710/LAN8720 2188000.ethernet-1:00: lan87xx_read_status failed: -110
> > 
> > So fix it by read_poll_timeout().
> 
> Do you have a more detailed explanation of what is going on here?
> 
> After a lot of thought, i think i can see how this happens. But the
> commit message should really spell out why this is the correct fix.
>
Hi Andrew:

Kevin report a bug for me in link[1], I check the Commit 7ae7ad2f11ef47
("net: phy: smsc: use phy_read_poll_timeout() to simplify the code") and
found it change the original behavior in smsc driver. It does not has
any error message whether it is timeout or phy_read fails, but this Commit
will changed it and will print some error messages by
phy_read_poll_timeout() when it is timeout or phy_read fails. so use the
read_poll_timeout() to replace phy_read_poll_timeout() to fix this
issue. the read_poll_timeout() does not print any log when it goes
wrong.

the original codes is that:

	/* Wait max 640 ms to detect energy */
	for (i = 0; i < 64; i++) {
	        /* Sleep to allow link test pulses to be sent */
	        msleep(10);
	        rc = phy_read(phydev, MII_LAN83C185_CTRL_STATUS);
	        if (rc < 0)
	                return rc;
	        if (rc & MII_LAN83C185_ENERGYON)
	                break;
	}

Commit 7ae7ad2f11ef47 modify it as this:

	phy_read_poll_timeout(phydev, MII_LAN83C185_CTRL_STATUS,
	                      rc & MII_LAN83C185_ENERGYON, 10000,
	                      640000, true);
	if (rc < 0)
	        return rc;

the phy_read_poll_timeout() will print a error log by phydev_err()
when timeout or rc < 0. read_poll_timeout() just return timeout
error and does not print any error log.

#define phy_read_poll_timeout(phydev, regnum, val, cond, sleep_us, \
                                timeout_us, sleep_before_read) \
({ \
        int __ret = read_poll_timeout(phy_read, val, (cond) || val < 0, \
                sleep_us, timeout_us, sleep_before_read, phydev, regnum); \
        if (val <  0) \
                __ret = val; \
        if (__ret) \
                phydev_err(phydev, "%s failed: %d\n", __func__, __ret); \
        __ret; \
})

So use read_poll_timeout Use read_poll_timeout() to be consistent with the
original code.

link[1]: https://lkml.org/lkml/2020/6/1/1408

> Thanks
> 	Andrew