Re: [PATCH net-next v3 2/4] dt-bindings: net: phy: add MaxLinear GPY2xx bindings

[Michael Walle]

Am 2023-01-13 17:38, schrieb Rob Herring:
> On Wed, Jan 11, 2023 at 4:30 PM Michael Walle <michael@xxxxxxxx> wrote:
> > Am 2023-01-11 21:26, schrieb Rob Herring:
> > > On Mon, Jan 09, 2023 at 01:30:11PM +0100, Michael Walle wrote:
> > >> Add the device tree bindings for the MaxLinear GPY2xx PHYs, which
> > >> essentially adds just one flag: maxlinear,use-broken-interrupts.
> > >>
> > >> One might argue, that if interrupts are broken, just don't use
> > >> the interrupt property in the first place. But it needs to be more
> > >> nuanced. First, this interrupt line is also used to wake up systems by
> > >> WoL, which has nothing to do with the (broken) PHY interrupt handling.
> > >
> > > I don't understand how this is useful. If the interrupt line is
> > > asserted
> > > after the 1st interrupt, how is it ever deasserted later on to be
> > > useful.
> >
> > Nobody said, that the interrupt line will stay asserted. The broken
> > behavior is that of the PHY doesn't respond *immediately* with a
> > deassertion of the interrupt line after the its internal status
> > register is cleared. Instead there is a random delay of up to 2ms.
>
> With only "keep the interrupt line asserted even after the interrupt
> status register is cleared", I assume that means forever, not some
> delay.

Fair enough. I'll send a doc patch.

> > There is already a workaround to avoid an interrupt storm by delaying
> > the ISR until the line is actually cleared. *But* if this line is
> > a shared one. The line is blocked by these 2ms and important
> > interrupts (like PTP timestaming) of other devices on this line
> > will get delayed. Therefore, the only viabale option is to disable
> > the interrupts handling in the broken PHY altogether. I.e. the line
> > will never be asserted by the broken PHY.
>
> Okay, that makes more sense.
>
> So really, this is just an 'is shared interrupt' flag. If not shared,
> then there's no reason to not use the interrupt?

Correct.

> Assuming all
> interrupts are described in DT, we already have that information. It's
> just hard and inefficient to get it. You have to parse all interrupts
> with the same parent and check for the same cells. If we're going to
> add something more explicit, we should consider something common. It's
> not the first time shared interrupts have come up, and we probably
> have some properties already. For something common, I'd probably make
> this a flag in interrupt cells rather than a property. That would
> handle cases with multiple interrupts better.

What kind of flag do you have in mind? Could you give an example?

-michael