From: Roelof Berg <rberg@berg-solutions.de>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Bryan Whitehead <bryan.whitehead@microchip.com>,
Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>,
"David S. Miller" <davem@davemloft.net>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] lan743x: Added fixed link support
Date: Tue, 19 May 2020 18:42:33 +0200 [thread overview]
Message-ID: <F241F806-3A08-4086-9739-361538FD246B@berg-solutions.de> (raw)
In-Reply-To: <20200518203447.GF624248@lunn.ch>
Hi Andrew,
thank you for the example, your input got me further. Sorry if my e-mails made the impression that the MAC is sending MDIO on its own. It can issue MDIO but I assume it will do this only on request of the MCU.
I read the data sheets again and found what might have confused us. There is:
a) Auto Negotiation (Phy-Phy)
b) Automatic Speed Detection, ASD (Mac-Phy)
c) Automatic Duplex Detection, ADD (Mac-Phy)
My current hypothesis is: When Phy-Phy auto negotiation is done, the ASD and ADD of the MAC will implicitly catch up the new mode of the Phy on a low level (clocks, pins). A dumb silicon would need the MCU to re-configure the MAC after MDIO told the MCU about a change in the Phy mode. But this ultra smart silicon would neither need MDIO, nor an MCU to understand what’s going on on the busses :)
If this hypothesis is correct, I should change in the driver all comments that mention „auto negoriation“ to „ADD, ASD“, and future readers will not be confused anymore.
Conclusion:
- Maybe I can leave ASD and ADD even active in fixed-link scenarios, when in the device tree an empty fixed-link node is present.
- And I need to disable ASD and/or ADD only if speed and/or duplex is configured inside the fixed-link mode.
I need to verify this hypothesis.
Thank you for reviewing and sharing topics we need to consider,
Roelof
> Am 18.05.2020 um 22:34 schrieb Andrew Lunn <andrew@lunn.ch>:
>
>> I double checked the vendor documentation and according to the data
>> sheet in this device the MAC detects speed and duplex mode. It uses
>> PINs, traces clocks … Also according to an application note of the
>> vendor duplex and speed detection should be enabled in the MAC
>> registers.
>
> In general, the MAC should not perform MDIO requests on the PHY. The
> MAC has no access to the mutex which phylib users. So if the MAC
> directly accesses registers in the PHY, it could do it at the wrong
> time, when the PHY driver is active.
>
> This can be particularly bad when Marvell PHYs are used. They have
> paged registers. One example is the page with the temperature sensor.
> This can be selected due to a read on the hwmon device. If the MAC
> tried to read the speed/duplex which the temperature sensor is
> selected, it would wrongly read the temperature sensor registers, not
> the link state.
>
> There is no need for the MAC to directly access the PHY. It will get
> told what the result of auto-neg is. So please turn this off all the
> time.
>
> Andrew
>
next prev parent reply other threads:[~2020-05-19 16:42 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-16 19:24 [PATCH] lan743x: Added fixed link support Roelof Berg
2020-05-17 18:37 ` Andrew Lunn
2020-05-17 20:44 ` Roelof Berg
2020-05-17 23:50 ` Andrew Lunn
2020-05-18 19:31 ` Roelof Berg
2020-05-18 20:34 ` Andrew Lunn
2020-05-19 16:42 ` Roelof Berg [this message]
2020-05-19 22:06 ` Ronnie.Kunin
2020-05-18 20:53 ` Bryan.Whitehead
2020-05-18 20:01 ` Roelof Berg
-- strict thread matches above, loose matches on Subject: below --
2020-05-20 17:10 Roelof Berg
2020-05-21 14:04 ` Andrew Lunn
2020-05-13 19:06 Roelof Berg
2020-05-13 19:17 ` Florian Fainelli
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