linux-kernel - Re: [PATCH] dp83640: Ensure against premature access to PHY registers after reset

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Message-Id: <20180406.111337.1908168293065420432.davem@davemloft.net>
Date:   Fri, 06 Apr 2018 11:13:37 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     andrew@...n.ch
Cc:     esben.haabendal@...il.com, netdev@...r.kernel.org, eha@...f.com,
        richardcochran@...il.com, f.fainelli@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dp83640: Ensure against premature access to PHY
 registers after reset

From: Andrew Lunn <andrew@...n.ch>
Date: Fri, 6 Apr 2018 16:14:10 +0200

> On Fri, Apr 06, 2018 at 04:05:40PM +0200, Esben Haabendal wrote:
>> From: Esben Haabendal <eha@...f.com>
>> 
>> Signed-off-by: Esben Haabendal <eha@...f.com>
>> ---
>>  drivers/net/phy/dp83640.c | 17 +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>> 
>> diff --git a/drivers/net/phy/dp83640.c b/drivers/net/phy/dp83640.c
>> index 654f42d00092..48403170096a 100644
>> --- a/drivers/net/phy/dp83640.c
>> +++ b/drivers/net/phy/dp83640.c
>> @@ -1207,6 +1207,22 @@ static void dp83640_remove(struct phy_device *phydev)
>>  	kfree(dp83640);
>>  }
>>  
>> +static int dp83640_soft_reset(struct phy_device *phydev)
>> +{
>> +	int ret;
>> +
>> +	ret = genphy_soft_reset(phydev);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	/* From DP83640 datasheet: "Software driver code must wait 3 us
>> +	 * following a software reset before allowing further serial MII
>> +	 * operations with the DP83640." */
>> +	udelay(3);
> 
> Hi Esben
> 
> The accuracy of udelay() is not guaranteed. So you probably want to be
> a bit pessimistic, and use 10.

Agreed.