linux-kernel - Re: [PATCH v1 2/2] mfd: Introduce QTI I2C PMIC controller

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Message-ID: <20200515104520.GK271301@dell>
Date:   Fri, 15 May 2020 11:45:20 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     devicetree@...r.kernel.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Subbaraman Narayanamurthy <subbaram@...eaurora.org>,
        David Collins <collinsd@...eaurora.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] mfd: Introduce QTI I2C PMIC controller

On Thu, 30 Apr 2020, Guru Das Srinagesh wrote:

> On Wed, Apr 29, 2020 at 08:50:10AM +0100, Lee Jones wrote:
> > On Tue, 28 Apr 2020, Guru Das Srinagesh wrote:
> > 
> > > The Qualcomm Technologies, Inc. I2C PMIC Controller is used by
> > > multi-function PMIC devices which communicate over the I2C bus.  The
> > > controller enumerates all child nodes as platform devices, and
> > > instantiates a regmap interface for them to communicate over the I2C
> > > bus.
> > > 
> > > The controller also controls interrupts for all of the children platform
> > > devices.  The controller handles the summary interrupt by deciphering
> > > which peripheral triggered the interrupt, and which of the peripheral
> > > interrupts were triggered.  Finally, it calls the interrupt handlers for
> > > each of the virtual interrupts that were registered.
> > > 
> > > Nicholas Troast is the original author of this driver.
> > > 
> > > Signed-off-by: Guru Das Srinagesh <gurus@...eaurora.org>
> > > ---
> > >  drivers/mfd/Kconfig         |  11 +
> > >  drivers/mfd/Makefile        |   1 +
> > >  drivers/mfd/qcom-i2c-pmic.c | 737 ++++++++++++++++++++++++++++++++++++++++++++
> > 
> > The vast majority of this driver deals with IRQ handling.  Why can't
> > this be split out into its own IRQ Chip driver and moved to
> > drivers/irqchip?
> 
> There appear to be quite a few in-tree MFD drivers that register IRQ
> controllers, like this driver does:
> 
> $ grep --exclude-dir=.git -rnE "irq_domain_(add|create).+\(" drivers/mfd | wc -l
> 23
> 
> As a further example, drivers/mfd/stpmic1.c closely resembles this
> driver in that it uses both devm_regmap_add_irq_chip() as well as
> devm_of_platform_populate().
> 
> As such, it seems like this driver is in line with some of the
> architectural choices that have been accepted in already-merged drivers.
> Could you please elaborate on your concerns?

It is true that *basic* IRQ domain support has been added to these
drivers in the past.  However, IMHO the support added to this driver
goes beyond those realms such that it would justify a driver of its
own.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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