RE: [PATCH] i3c: dw: Disable IBI IRQ depends on hot-join and SIR enabling

[Dylan Hung]

Hi Jeremy,

> -----Original Message-----
> From: Jeremy Kerr <jk@xxxxxxxxxxxxxxxxxxxx>
> Sent: Monday, May 6, 2024 1:10 PM
> To: Dylan Hung <dylan_hung@xxxxxxxxxxxxxx>;
> alexandre.belloni@xxxxxxxxxxx; joel@xxxxxxxxx; u.kleine-
> koenig@xxxxxxxxxxxxxx; gustavoars@xxxxxxxxxx;
> krzysztof.kozlowski@xxxxxxxxxx; zenghuchen@xxxxxxxxxx;
> matt@xxxxxxxxxxxxxxxxxxxx; linux-i3c@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Cc: BMC-SW <BMC-SW@xxxxxxxxxxxxxx>
> Subject: Re: [PATCH] i3c: dw: Disable IBI IRQ depends on hot-join and SIR
> enabling
> 
> Hi Dylan,
> 
> Thanks for the response! I have a couple of follow-up things though:
> 
> > > My interpretation of this change is that we keep the "global" IBI
> > > irq enabled if hot-join-nack is set (ie, always, because we don't
> > > support hot join, and configure the hardware to nack all hot join
> requests).
> > >
> > I would like to clarify the control logic, incorporating the principle
> > of disabling the SIR interrupt signal:
> >
> > Case 1:
> > When `DEV_CTRL_HOT_JOIN_NACK` is set, indicating `hj_rejected` is
> > true, it signifies the controller's non-receptiveness to the hot-join
> > event. Consequently, we can safely disable the SIR interrupt signal if
> > none of the target devices request SIR (reg == 0xffffffff).
> >
> > Case 2:
> > When `DEV_CTRL_HOT_JOIN_NACK` is unset, indicating `hj_rejected` is
> > false, this indicates the controller's readiness to engage with the
> > hot-join event. Therefore, it's imperative to keep the SIR interrupt
> > signal enabled, even if not all target devices request SIR. In this
> > case, `global` is false and `enable` is false.
> 
> Yep, I see what you're doing there, but it looks like the correct state would
> never be set if we're not enabling/disabling the IBIs separately; with this code,
> we would only ever enable the SIR for the HJ if we
> *also* happen to enable IBIs.

When we want to enable the SIR, the current code doesn't check whether the
hot-join is enable or not. The modification I made pertains to disabling the SIR interrupt.
It doesn't alter the logic for enabling the SIR.

```
	reg = readl(master->regs + IBI_SIR_REQ_REJECT);
	if (enable) {
		global = reg == 0xffffffff;
		reg &= ~BIT(idx);
	}
```

> 
> The initial state would be to have all SIRs masked.
> 

Yes, indeed. The "global" variable is also true because "reg == 0xffffffff" is true.
Therefore, the INTR_IBI_THLD_STAT bit will be set in the following code.

> > Billy recently submitted a change to implement the hot-join
> enabling/disabling. Therefore, it is timely to consider the hot-join
> functionality.
> > https://patchwork.kernel.org/project/linux-i3c/patch/20240429073624.25
> > 6830-1-billy_tsai@xxxxxxxxxxxxxx/
> 
> Yep, I saw that, excellent! It's next on my list to take a look at.
> 
> It's just a little unusual that we're enabling the HJ interrupt before actually
> having the HJ support though.
> 
> Cheers,
> 
> 
> Jeremy