Merge branch 'net-phy-add-support-for-shared-interrupts-part-1'

Merge branch 'net-phy-add-support-for-shared-interrupts-part-1'

Ioana Ciornei says:

====================
net: phy: add support for shared interrupts (part 1)

This patch set aims to actually add support for shared interrupts in
phylib and not only for multi-PHY devices. While we are at it,
streamline the interrupt handling in phylib.

For a bit of context, at the moment, there are multiple phy_driver ops
that deal with this subject:

- .config_intr() - Enable/disable the interrupt line.

- .ack_interrupt() - Should quiesce any interrupts that may have been
  fired.  It's also used by phylib in conjunction with .config_intr() to
  clear any pending interrupts after the line was disabled, and before
  it is going to be enabled.

- .did_interrupt() - Intended for multi-PHY devices with a shared IRQ
  line and used by phylib to discern which PHY from the package was the
  one that actually fired the interrupt.

- .handle_interrupt() - Completely overrides the default interrupt
  handling logic from phylib. The PHY driver is responsible for checking
  if any interrupt was fired by the respective PHY and choose
  accordingly if it's the one that should trigger the link state machine.

From my point of view, the interrupt handling in phylib has become
somewhat confusing with all these callbacks that actually read the same
PHY register - the interrupt status.  A more streamlined approach would
be to just move the responsibility to write an interrupt handler to the
driver (as any other device driver does) and make .handle_interrupt()
the only way to deal with interrupts.

Another advantage with this approach would be that phylib would gain
support for shared IRQs between different PHY (not just multi-PHY
devices), something which at the moment would require extending every
PHY driver anyway in order to implement their .did_interrupt() callback
and duplicate the same logic as in .ack_interrupt(). The disadvantage
of making .did_interrupt() mandatory would be that we are slightly
changing the semantics of the phylib API and that would increase
confusion instead of reducing it.

What I am proposing is the following:

- As a first step, make the .ack_interrupt() callback optional so that
  we do not break any PHY driver amid the transition.

- Every PHY driver gains a .handle_interrupt() implementation that, for
  the most part, would look like below:

	irq_status = phy_read(phydev, INTR_STATUS);
	if (irq_status < 0) {
		phy_error(phydev);
		return IRQ_NONE;
	}

	if (!(irq_status & irq_mask))
		return IRQ_NONE;

	phy_trigger_machine(phydev);

	return IRQ_HANDLED;

- Remove each PHY driver's implementation of the .ack_interrupt() by
  actually taking care of quiescing any pending interrupts before
  enabling/after disabling the interrupt line.

- Finally, after all drivers have been ported, remove the
  .ack_interrupt() and .did_interrupt() callbacks from phy_driver.

This patch set is part 1 and it addresses the changes needed in phylib
and 7 PHY drivers. The rest can be found on my Github branch here:
https://github.com/IoanaCiornei/linux/commits/phylib-shared-irq

I do not have access to most of these PHY's, therefore I Cc-ed the
latest contributors to the individual PHY drivers in order to have
access, hopefully, to more regression testing.

Changes in v2:
 - Rework the .handle_interrupt() implementation for each driver so that
   only the enabled interrupts are taken into account when
   IRQ_NONE/IRQ_HANDLED it returned. The main idea is so that we avoid
   falsely blaming a device for triggering an interrupt when this is not
   the case.
   The only devices for which I was unable to make this adjustment were
   the BCM8706, BCM8727, BCMAC131 and BCM5241 since I do not have access
   to their datasheets.
 - I also updated the pseudo-code added in the cover-letter so that it's
   more clear how a .handle_interrupt() callback should look like.
====================

Tested-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20201101125114.1316879-1-ciorneiioana@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>