Re: [PATCH 09/12] irqchip: cirrus: Add driver for Cirrus Logic CS48L31/32/33 codecs

[Marc Zyngier <maz@xxxxxxxxxx>]

On Thu, 10 Nov 2022 16:31:06 +0000,
Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx> wrote:
> 
> On 10/11/2022 15:13, Marc Zyngier wrote:
> > On Thu, 10 Nov 2022 13:00:50 +0000,
> > Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx> wrote:
> >> 
> >> On 10/11/2022 12:01, Marc Zyngier wrote:
> >>> On Thu, 10 Nov 2022 11:22:26 +0000,
> >>> Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx> wrote:
> >>>> 
> >>>> On 10/11/2022 08:02, Marc Zyngier wrote:
> >>>>> On Wed, 09 Nov 2022 16:53:28 +0000,
> >>>>> Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx> wrote:
> >>>>>> 
> >>>>>> The Cirrus Logic CS48L31/32/33 audio codecs contain a programmable
> >>>>>> interrupt controller with a variety of interrupt sources, including
> >>>>>> GPIOs that can be used as interrupt inputs.
> >>>>>> 
> >>>>>> This driver provides the handling for the interrupt controller. As the
> >>>>>> codec is accessed via regmap, the generic regmap_irq functionality
> >>>>>> is used to do most of the work.
> >>>>>> 
> >>>>> 
> >>>>> I cannot spot a shred of interrupt controller code in there. This
> >>>> 
> >>>> It is providing support for handling an interrupt controller so that
> >>>> other drivers can bind to those interrupts. It's just that regmap
> >>>> provides a lot of generic implementation for SPI-connected interrupt
> >>>> controllers so we don't need to open-code all that in the
> >>>> irqchip driver.
> >>> 
> >>> And thus none of that code needs to live in drivers/irqchip.
> >>> 
> >>>> 
> >>>>> belongs IMO to the MFD code.
> >>>> 
> >>>> We did once put interrupt support in MFD for an older product line but
> >>>> the MFD maintainer doesn't like the MFD being a dumping-ground for
> >>>> random other functionality that have their own subsystems.
> >>> 
> >>> I don't like this stuff either. All this code is a glorified set of
> >>> interrupt handlers and #defines that only hide the lack of a proper DT
> >>> binding to express the interrupt routing (it feels like looking at
> >>> board files from 10 years ago).
> >>> 
> >> 
> >> I didn't understand this. The whole purpose of this is to instantiate
> >> Linux interrupts for the PIC interrupt sources so that other drivers
> >> that want to use the interrupts from the CS48L32 PIC can use standard
> >> kernel APIs or DT to bind against them.
> > 
> > There is zero standard APIs in this patch. Does cs48l32_request_irq()
> > look standard to you? This whole thing makes a mockery of the
> > interrupt model and of firmware-based interrupt description which we
> > spent years to build.
> > 
> >> 
> >> The four handlers registered within the driver are done here simply
> >> because they don't belong to any particular child driver. Since they
> >> are a fixed feature of the chip that we know we want to handle we may as
> >> well just register them.
> > 
> > Again, they have no purpose in an interrupt controller driver.
> > 
> >> If we put them in the MFD with DT definitions it would make a
> >> circular dependency between MFD and its child, which is not a great
> >> situation. If it's these handlers that are bothering you, we could move
> >> them to the audio driver.
> > 
> > And what's left? Nothing.
> 
> Ah, I see. You've missed that the bulk of the implementation re-uses
> existing library code from regmap. It does say this in the commit
> message.
> 
>   "the generic regmap_irq functionality is used to do most of the work."
> 
> and I've also said this in previous replies.
> 
> This is no way driver that does nothing. There's over 1000 lines of code
> handling the PIC and dispatching its interrupts to other drivers that
> want to bind to them. It's just that it makes no sense to duplicate 1300
> lines of interrupt handling code from elsewhere when we can re-use that
> by calling regmap_add_irq_chip(). That gives us all the interrupt-
> controller-handling code in drivers/base/regmap/regmap-irq.c
> 
> Perhaps you could re-review this taking into account that
> regmap_add_irq_chip() is significant.

Read again what I have written. Having to expose a device-specific API
for endpoint drivers to obtain their interrupts, and requiring them to
know about some magic values that describe the interrupts source are
not a acceptable constructs.

We have firmware descriptions to expose interrupt linkages, and your
HW is not special enough to deserve its own top level API. Yes, we
accepted such drivers in the past, but it has to stop.

Either you describe the internal structure of your device in DT or
ACPI, and make all client drivers use the standard API, or you make
this a codec library, purely specific to your device and only used by
it. But the current shape is not something I'm prepared to accept.

	M.

-- 
Without deviation from the norm, progress is not possible.