On 30/07/2024 10:41, Russell King (Oracle) wrote:
On Tue, Jul 30, 2024 at 10:36:12AM +0100, Jon Hunter wrote:
On 29/07/2024 11:47, Russell King (Oracle) wrote:
...
Apologies for not following up before on this and now that is has been a
year I am not sure if it is even appropriate to dig this up as opposed to
starting a new thread completely.
However, I want to resume this conversation because we have found that this
change does resolve a long-standing issue where we occasionally see our
ethernet controller fail to get an IP address.
I understand that your objection to the above change is that (per Revanth's
feedback) this change assumes interface has the link. However, looking at
the aqr107_read_status() function where this change is made the function has
the following ...
static int aqr107_read_status(struct phy_device *phydev)
{
int val, ret;
ret = aqr_read_status(phydev);
if (ret)
return ret;
if (!phydev->link || phydev->autoneg == AUTONEG_DISABLE)
return 0;
So my understanding is that if we don't have the link, then the above test
will return before we attempt to poll the TX ready status. If that is the
case, then would the change being proposed be OK?
Here, phydev->link will be the _media_ side link. This is fine - if the
media link is down, there's no point doing anything further. However,
if the link is up, then we need the PHY to update phydev->interface
_and_ report that the link was up (phydev->link is true).
When that happens, the layers above (e.g. phylib, phylink, MAC driver)
then know that the _media_ side interface has come up, and they also
know the parameters that were negotiated. They also know what interface
mode the PHY is wanting to use.
At that point, the MAC driver can then reconfigure its PHY facing
interface according to what the PHY is using. Until that point, there
is a very real chance that the PHY <--> MAC connection will remain
_down_.
The patch adds up to a _two_ _second_ wait for the PHY <--> MAC
connection to come up before aqr107_read_status() will return. This
is total nonsense - because waiting here means that the MAC won't
get the notification of which interface mode the PHY is expecting
to use, therefore the MAC won't configure its PHY facing hardware
for that interface mode, and therefore the PHY <--> MAC connection
will _not_ _come_ _up_.
You can not wait for the PHY <--> MAC connection to come up in the
phylib read_status method. Ever.
This is non-negotiable because it is just totally wrong to do this
and leads to pointless two second delays.
Thanks for the feedback! We will go away, review this and see if we can
figure out a good/correct way to resolve our ethernet issue.
Which ethernet driver is having a problem?
It is the drivers/net/ethernet/stmicro/stmmac/dwmac-tegra.c driver. It
works most of the time, but on occasion it fails to get a valid IP
address.
Thanks
Jon
--
nvpublic
