netdev - Re: [RFC PATCH 2/2] net: phy: dp83869: fix mii mode when rgmii strap cfg is used

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Date:   Thu, 27 Apr 2023 09:38:48 +0530
From:   Siddharth Vadapalli <s-vadapalli@...com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     <hkallweit1@...il.com>, <linux@...linux.org.uk>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <srk@...com>,
        <s-vadapalli@...com>
Subject: Re: [RFC PATCH 2/2] net: phy: dp83869: fix mii mode when rgmii strap
 cfg is used



On 26/04/23 18:11, Andrew Lunn wrote:
>>>> @@ -692,8 +692,11 @@ static int dp83869_configure_mode(struct phy_device *phydev,
>>>>  	/* Below init sequence for each operational mode is defined in
>>>>  	 * section 9.4.8 of the datasheet.
>>>>  	 */
>>>> +	phy_ctrl_val = dp83869->mode;
>>>> +	if (phydev->interface == PHY_INTERFACE_MODE_MII)
>>>> +		phy_ctrl_val |= DP83869_OP_MODE_MII;
>>>
>>> Should there be some validation here with dp83869->mode?
>>>
>>> DP83869_RGMII_COPPER_ETHERNET, DP83869_RGMII_SGMII_BRIDGE etc don't
>>> make sense if MII is being used. DP83869_100M_MEDIA_CONVERT and maybe
>>> DP83869_RGMII_100_BASE seem to be the only valid modes with MII?
>>
>> The DP83869_OP_MODE_MII macro corresponds to BIT(5) which is the RGMII_MII_SEL
>> bit in the OP_MODE_DECODE register. If the RGMII_MII_SEL bit is set, MII mode is
>> selected. If the bit is cleared, which is the default value, RGMII mode is
>> selected. As pointed out by you, there are modes which aren't valid with MII
>> mode. However, a mode which isn't valid with RGMII mode (default value of the
>> RGMII_MII_SEL bit) also exists: DP83869_SGMII_COPPER_ETHERNET. For this reason,
>> I believe that setting the bit when MII mode is requested shouldn't cause any
>> issues.
> 
> If you say so. I was just thinking you could give the poor software
> engineer a hint the hardware engineer has put on strapping resistors
> which means the PHY is not going to work.

I understand now. I will update this patch to add a print if the MII mode is not
valid with the configured "dp83869->mode". Would you suggest using a dev_err()
or a dev_dbg()?

Thank you for the feedback on this series.

-- 
Regards,
Siddharth.