Date:   Mon, 25 May 2020 18:22:19 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, andrew@...n.ch,
        f.fainelli@...il.com, hkallweit1@...il.com,
        madalin.bucur@....nxp.com, calvin.johnson@....nxp.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 04/11] net: phy: Handle c22 regs presence better

On 5/25/20 6:09 PM, Russell King - ARM Linux admin wrote:
> On Mon, May 25, 2020 at 05:22:07PM -0500, Jeremy Linton wrote:
>> 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 <jeremy.linton@....com>
>>>>>>>> ---
>>>>>>>>      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.
>>
>> Probably...
>>
>> 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).
> 
> I think I've just flattened that argument in my immediately preceding
> reply on the Cortina situation; I think you've grossly misread that
> through not fully researching the history and then finding the
> existing users.
> 
> There is no bug that you are fixing from what I can see.

One of us is missing something,

The "cortina" solution is broken in the current kernel. That is because 
lines 726-742 are dead code due to line 693.

I believe I've understood the problem there, and corrected it in this 
set along with a few others, but its distinctly possible that isn't true.

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