linux-kernel - Re: [PATCH RFC v2 06/14] dt-bindings/interrupt-controller: pdc: add SPI config register

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Message-ID: <5dc219a0.1c69fb81.f5014.42d2@mx.google.com>
Date:   Tue, 05 Nov 2019 16:53:51 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Lina Iyer <ilina@...eaurora.org>
Cc:     evgreen@...omium.org, linus.walleij@...aro.org, maz@...nel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        bjorn.andersson@...aro.org, mkshah@...eaurora.org,
        linux-gpio@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH RFC v2 06/14] dt-bindings/interrupt-controller: pdc: add SPI config register

Quoting Lina Iyer (2019-11-05 12:58:32)
> On Tue, Oct 15 2019 at 00:27 -0600, Stephen Boyd wrote:
> >
> >I had another idea the other day. Maybe a better approach would be to
> >make the mailbox or SCM code an interrupt controller with the
> >appropriate functions to poke the bits necessary to make the interrupts
> >work. Then we can make it a chip in the hierarchy between the GIC and
> >PDC and make the interrupts call through from PDC to GIC. The locking
> >could be handled in each respective driver if necessary, and otherwise
> >we don't have to use a regmap or remap the same registers (except we may
> >need to describe if the parent is the mailbox node or the scm fimware
> >node).
> >
> Wouldn't that be a stretch to image the SCM register write  or a random
> register write as an interrupt controller? But I agree that it solves
> the issue of determining whether we want to use SCM or regmap.

As far as I can tell it's similar to PDC which is basically a gate on
the line from a dedicated chip pad or a GPIO pad that lets the interrupt
flow through to the GIC or not. Isn't this yet another hardware block on
those paths that control the edge type or something?

> 
> But, we would still need to add syscon to the mailbox and then regmap
> the registers for the interrupt contoller.

I'm saying that we can make the mailbox driver an interrupt controller
driver too. Or if that doesn't work, we can map the region twice in each
driver with ioremap and cross fingers that they don't touch the same
register at the same time. It sounds like that is the case. We won't be
able to fancily reserve the register region and map it in one function
call, but maybe that can be fixed by limiting the size or offset that is
reserved for each driver manually based on the same register property
that's described in DT. Basically, one node in DT

 mailbox@f00 {
   reg = <0xf00 0x1000>;
 };

And then each driver will ioremap() the whole register region that's
parsed from DT but each driver will mark sub-regions as reserved for the
respective driver. That way we don't have to worry about using a regmap
here and we'll still know what drivers are using what regions of IO in
/proc/iomem.