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SubjectRe: [PATCH RFC v2 06/14] dt-bindings/interrupt-controller: pdc: add SPI config register
On Tue, Nov 05 2019 at 17:53 -0700, Stephen Boyd wrote:
>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

Marc: What do you think of Stephen's idea? Summarizing my understanding
below -

We need to set an addition register for GPIOs that are routed to PDC and
the register may need to be written using a SCM call (SDM845) or written
from Linux (SDM855). The idea proposed here is -
Create multiple irqchips, one for each type of register access and then
put them in hierarchy based on the target.



The hierarchy would be explicit from the DT. So we would not have to
worry about figuring out using a property in DT or resource name. (May
be we can use a compatible instead?). The use of reserved_resource(),
suggested by Stephen, would help avoid other drivers writing to this
register which is part of a generic dump area for one-off registers.


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