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Date:   Mon, 25 May 2020 17:22:07 -0500
From:   Jeremy Linton <>
To:     Russell King - ARM Linux admin <>
Subject: Re: [RFC 04/11] net: phy: Handle c22 regs presence better

On 5/25/20 5:01 PM, Russell King - ARM Linux admin wrote:
> On Mon, May 25, 2020 at 04:51:16PM -0500, Jeremy Linton wrote:
>> Hi,
>> On 5/25/20 5:06 AM, Russell King - ARM Linux admin wrote:
>>> On Sun, May 24, 2020 at 10:34:13PM -0500, Jeremy Linton wrote:
>>>> Hi,
>>>> On 5/23/20 1:37 PM, Russell King - ARM Linux admin wrote:
>>>>> On Fri, May 22, 2020 at 04:30:52PM -0500, Jeremy Linton wrote:
>>>>>> Until this point, we have been sanitizing the c22
>>>>>> regs presence bit out of all the MMD device lists.
>>>>>> This is incorrect as it causes the 0xFFFFFFFF checks
>>>>>> to incorrectly fail. Further, it turns out that we
>>>>>> want to utilize this flag to make a determination that
>>>>>> there is actually a phy at this location and we should
>>>>>> be accessing it using c22.
>>>>>> Signed-off-by: Jeremy Linton <>
>>>>>> ---
>>>>>>     drivers/net/phy/phy_device.c | 16 +++++++++++++---
>>>>>>     1 file changed, 13 insertions(+), 3 deletions(-)
>>>>>> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
>>>>>> index f0761fa5e40b..2d677490ecab 100644
>>>>>> --- a/drivers/net/phy/phy_device.c
>>>>>> +++ b/drivers/net/phy/phy_device.c
>>>>>> @@ -689,9 +689,6 @@ static int get_phy_c45_devs_in_pkg(struct mii_bus *bus, int addr, int dev_addr,
>>>>>>     		return -EIO;
>>>>>>     	*devices_in_package |= phy_reg;
>>>>>> -	/* Bit 0 doesn't represent a device, it indicates c22 regs presence */
>>>>>> -	*devices_in_package &= ~BIT(0);
>>>>>> -
>>>>>>     	return 0;
>>>>>>     }
>>>>>> @@ -742,6 +739,8 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id,
>>>>>>     	int i;
>>>>>>     	const int num_ids = ARRAY_SIZE(c45_ids->device_ids);
>>>>>>     	u32 *devs = &c45_ids->devices_in_package;
>>>>>> +	bool c22_present = false;
>>>>>> +	bool valid_id = false;
>>>>>>     	/* Find first non-zero Devices In package. Device zero is reserved
>>>>>>     	 * for 802.3 c45 complied PHYs, so don't probe it at first.
>>>>>> @@ -770,6 +769,10 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id,
>>>>>>     		return 0;
>>>>>>     	}
>>>>>> +	/* Bit 0 doesn't represent a device, it indicates c22 regs presence */
>>>>>> +	c22_present = *devs & BIT(0);
>>>>>> +	*devs &= ~BIT(0);
>>>>>> +
>>>>>>     	/* Now probe Device Identifiers for each device present. */
>>>>>>     	for (i = 1; i < num_ids; i++) {
>>>>>>     		if (!(c45_ids->devices_in_package & (1 << i)))
>>>>>> @@ -778,6 +781,13 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id,
>>>>>>     		ret = _get_phy_id(bus, addr, i, &c45_ids->device_ids[i], true);
>>>>>>     		if (ret < 0)
>>>>>>     			return ret;
>>>>>> +		if (valid_phy_id(c45_ids->device_ids[i]))
>>>>>> +			valid_id = true;
>>>>> Here you are using your "devices in package" validator to validate the
>>>>> PHY ID value.  One of the things it does is mask this value with
>>>>> 0x1fffffff.  That means you lose some of the vendor OUI.  To me, this
>>>>> looks completely wrong.
>>>> I think in this case I was just using it like the comment in
>>>> get_phy_device() "if the phy_id is mostly F's, there is no device here".
>>>> My understanding is that the code is trying to avoid the 0xFFFFFFFF returns
>>>> that seem to indicate "bus ok, phy didn't respond".
>>>> I just checked the OUI registration, and while there are a couple OUI's
>>>> registered that have a number of FFF's in them, none of those cases seems to
>>>> overlap sufficiently to cause this to throw them out. Plus a phy would also
>>>> have to have model+revision set to 'F's. So while might be possible, if
>>>> unlikely, at the moment I think the OUI registration keeps this from being a
>>>> problem. Particularly, if i'm reading the mapping correctly, the OUI mapping
>>>> guarantees that the field cannot be all '1's due to the OUI having X & M
>>>> bits cleared. It sort of looks like the mapping is trying to lose those
>>>> bits, by tossing bit 1 & 2, but the X & M are in the wrong octet (AFAIK, I
>>>> just read it three times cause it didn't make any sense).
>>> I should also note that we have at least one supported PHY where one
>>> of the MMDs returns 0xfffe for even numbered registers and 0x0000 for
>>> odd numbered registers in one of the vendor MMDs for addresses 0
>>> through 0xefff - which has a bit set in the devices-in-package.
>>> It also returns 0x0082 for almost every register in MMD 2, but MMD 2's
>>> devices-in-package bit is clear in most of the valid MMDs, so we
>>> shouldn't touch it.
>>> These reveal the problem of randomly probing MMDs - they can return
>>> unexpected values and not be as well behaved as we would like them to
>>> be.  Using register 8 to detect presence may be beneficial, but that
>>> may also introduce problems as we haven't used that before (and we
>>> don't know whether any PHY that wrong.)  I know at least the 88x3310
>>> gets it right for all except the vendor MMDs, where the low addresses
>>> appear non-confromant to the 802.3 specs.  Both vendor MMDs are
>>> definitely implemented, just not with anything conforming to 802.3.
>> Yes, we know even for the NXP reference hardware, one of the phy's doesn't
>> probe out correctly because it doesn't respond to the ieee defined
>> registers. I think at this point, there really isn't anything we can do
>> about that unless we involve the (ACPI) firmware in currently nonstandard
>> behaviors.
>> So, my goals here have been to first, not break anything, and then do a
>> slightly better job finding phy's that are (mostly?) responding correctly to
>> the 802.3 spec. So we can say "if you hardware is ACPI conformant, and you
>> have IEEE conformant phy's you should be ok". So, for your example phy, I
>> guess the immediate answer is "use DT" or "find a conformant phy", or even
>> "abstract it in the firmware and use a mailbox interface".
> You haven't understood.  The PHY does conform for most of the MMDs,
> but there are a number that do not conform.


Except that i'm not sure how that is a problem at the moment, its still 
going to trigger as a found phy, and walk the same mmd list as before 
requesting drivers. Those drivers haven't changed their behavior so 
where is the problem? If there is a problem its in 7/11 where things are 
getting kicked due to seemingly invalid Ids.

The 1/11 devices=0 case actually appears to be a bug i'm fixing because 
you won't get an ID or a MMD list from that (before or after).

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