On 9/3/2020 12:21 PM, Adam Rudziński wrote:
W dniu 2020-09-03 o 19:17, Florian Fainelli pisze:
On 9/3/2020 10:13 AM, Adam Rudziński wrote:
W dniu 2020-09-03 o 17:21, Florian Fainelli pisze:
On 9/2/2020 11:00 PM, Adam Rudziński wrote:
W dniu 2020-09-03 o 04:13, Florian Fainelli pisze:
On 9/2/2020 3:20 PM, Andrew Lunn wrote:
+ priv->clk = devm_clk_get_optional(&phydev->mdio.dev,
"sw_gphy");
+ if (IS_ERR(priv->clk))
+ return PTR_ERR(priv->clk);
+
+ /* To get there, the mdiobus registration logic already
enabled our
+ * clock otherwise we would not have probed this device
since we would
+ * not be able to read its ID. To avoid artificially
bumping up the
+ * clock reference count, only do the clock enable from a
phy_remove ->
+ * phy_probe path (driver unbind, then rebind).
+ */
+ if (!__clk_is_enabled(priv->clk))
+ ret = clk_prepare_enable(priv->clk);
This i don't get. The clock subsystem does reference counting. So
what
i would expect to happen is that during scanning of the bus, phylib
enables the clock and keeps it enabled until after probe. To keep
things balanced, phylib would disable the clock after probe.
That would be fine, although it assumes that the individual PHY
drivers have obtained the clocks and called clk_prepare_enable(),
which is a fair assumption I suppose.
If the driver wants the clock enabled all the time, it can enable it
in the probe method. The common clock framework will then have two
reference counts for the clock, so that when the probe exists, and
phylib disables the clock, the CCF keeps the clock ticking. The PHY
driver can then disable the clock in .remove.
But then the lowest count you will have is 1, which will lead to
the clock being left on despite having unbound the PHY driver from
the device (->remove was called). This does not allow saving any
power unfortunately.
There are some PHYs which will enumerate with the clock disabled.
They
only need it ticking for packet transfer. Such PHY drivers can
enable
the clock only when needed in order to save some power when the
interface is administratively down.
Then the best approach would be for the OF scanning code to enable
all clocks reference by the Ethernet PHY node (like it does in the
proposed patch), since there is no knowledge of which clock is
necessary and all must be assumed to be critical for MDIO bus
scanning. Right before drv->probe() we drop all resources
reference counts, and from there on ->probe() is assumed to manage
the necessary clocks.
It looks like another solution may be to use the assigned-clocks
property which will take care of assigning clock references to
devices and having those applied as soon as the clock provider is
available.
Hi Guys,
I've just realized that a PHY may also have a reset signal
connected. The reset signal may be controlled by the dedicated
peripheral or by GPIO.
There is already support for such a thing within
drivers/net/phy/mdio_bus.c though it assumes we could bind the PHY
device to its driver already.
In general terms, there might be a set of control signals needed to
enable the PHY. It seems that the clock and the reset would be the
typical useful options.
Going further with my imagination of how evil the hardware design
could be, in general the signals for the PHY may have some
relations to other control signals.
I think that from the software point of view this comes down to
assumption that the PHY is to be controlled "driver only knows how".
That is all well and good as long as we can actually bind the PHY
device which its driver, and right now this means that we either have:
- a compatible string in Device Tree which is of the form
ethernet-phy-id%4x.%4x (see of_get_phy_id) which means that we
*know* already which PHY we have and we avoid doing reads of
MII_PHYSID1 and MII_PHYSID2. This is a Linux implementation detail
that should not have to be known to systems designer IMHO
- a successful read of MII_PHYSID1 and MII_PHYSID2 (or an equivalent
for the clause 45 PHYs) that allows us to know what PHY device we
have, which is something that needs to happen eventually.
The problem is when there are essential resources such as clocks,
regulators, reset signals that must be enabled, respectively
de-asserted in order for a successful MDIO read of MII_PHYSID1 and
MII_PHYSID2 to succeed.
There is no driver involvement at that stage because we have no
phy_device to bind it to *yet*. Depending on what we read from
MII_PHYSID1/PHY_ID2 we will either successfully bind to the Generic
PHY driver (assuming we did not read all Fs) or not and we will
return -ENODEV and then it is game over.
This is the chicken and egg problem that this patch series is
addressing, for clocks, because we can retrieve clock devices with
just a device_node reference.
I have an impression that here the effort goes in the wrong
direction. If I understand correctly, the goal is to have the kernel
find out what will the driver need to use the phy. But, the kernel
anyway calls a probe function of the driver, doesn't it? To me it
looks as if you were trying to do something that the driver
will/would/might do later, and possibly "undo" it in the meantime. In
this regard, this becomes kind of a workaround, not solution of the
problem. Also, having taken a glance at your previous messages, I can
tell that this is all becoming even more complex.
What is the problem according to you, and what would an acceptable
solution look like then?
I think that the effort should be to allow any node in the device
tree to take care about its child nodes by itself, and just "report"
to the kernel, or "install" in the kernel whatever is necessary, but
without any initiative of the kernel. Let the drivers be as
complicated as necessary, not the kernel.
The Device Tree representation is already correct in that it lists
clocks/regulators/reset signals that are needed by the PHY. The
problem is its implementation with the Linux device driver model.
Please read again what I wrote.
The problem which I had, was that kernel was unable to read ID of second
PHY, because it needed to have the clock enabled, and during probing it
still didn't have. I don't know what problems are addressed by the
discussed patches - only the same one, or if something else too.
That is precisely the problem being addressed here, an essential clock
to the PHY must be enabled for the PHY to be accessible on the MDIO bus.
In my solution, of my problem, which now works well for me, instead of
teaching kernel any new tricks, I've taught the kernel to listen to the
driver, by adding a function allowing the driver to register its PHY on
the MDIO bus at any time. Then, each driver instance (for a particular
interface) configures whatever is necessary, finds its PHY when probing
the shared MDIO bus, and tells the kernel(?) to add it to the shared
MDIO bus. Since each one does that, when the time comes, all PHYs are
known and all interfaces are up.
Except this is bending the Linux driver model backwards, a driver does
not register devices, a bus does, and then it binds the driver to that
device object. For the bus to scan a hardware device, said hardware
device must be in a functional state to be discovered.
This is just an example. It doesn't need the kernel to mimic the driver.
But, it requires a bit different structure of the device tree, and I
guess I'm not aware of tons of reasons for which it's not "the good
way". Sorry, I can't be more constructive here, I don't have that much
experience with the kernel. The idea is simple: the driver does the job,
not the kernel.
You know much better than me how Linux works, so you decide if this
makes sense, or not, and what does this actually mean in the context of
the system.
Concerning invalid PHY ID, all Fs are read when the MDIO bus works, but
the PHY is inactive. Another invalid ID is all 0s. I have seen this
value when the MDIO bus didn't have the pins assigned, so its signals
were "trapped" in the processor. Another cause could be a physical fault
(short?) on the bus. Maybe this case should end up in returning -ENODEV
too.
Read failures are already treated as such, there is no need to change
anything here.
--
Florian
