linux-kernel - Re: [PATCH RESEND] mfd: Add Freescale i.MX8qxp Control and Status Registers (CSR) module driver

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Message-ID: <afa29fcc11436dd957314a4066c9141937f0470c.camel@nxp.com>
Date:   Tue, 01 Nov 2022 13:53:49 +0800
From:   Liu Ying <victor.liu@....com>
To:     Lee Jones <lee@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, linux-imx@....com
Subject: Re: [PATCH RESEND] mfd: Add Freescale i.MX8qxp Control and Status
 Registers (CSR) module driver

Hi Lee,

On Mon, 2022-10-31 at 15:40 +0000, Lee Jones wrote:
> On Mon, 17 Oct 2022, Liu Ying wrote:
> 
> > Freescale i.MX8qxp Control and Status Registers (CSR) module is a system
> > controller. It represents a set of miscellaneous registers of a specific
> > subsystem. It may provide control and/or status report interfaces to a
> > mix of standalone hardware devices within that subsystem.
> > 
> > The CSR module in i.MX8qm/qxp SoCs is a child node of a simple power-managed
> > bus(i.MX8qxp pixel link MSI bus). To propagate power management operations
> > of the CSR module's child devices to that simple power-managed bus, add a
> > dedicated driver for the CSR module. Also, the driver would populate the CSR
> > module's child devices.
> > 
> > Signed-off-by: Liu Ying <victor.liu@....com>
> > ---
> > The Freescale i.MX8qxp CSR DT bindings is at
> > Documentation/devicetree/bindings/mfd/fsl,imx8qxp-csr.yaml.
> > 
> > Resend the patch based on v6.1-rc1.
> > 
> >  drivers/mfd/Kconfig           | 10 +++++++
> >  drivers/mfd/Makefile          |  1 +
> >  drivers/mfd/fsl-imx8qxp-csr.c | 53 +++++++++++++++++++++++++++++++++++
> >  3 files changed, 64 insertions(+)
> >  create mode 100644 drivers/mfd/fsl-imx8qxp-csr.c

[...]

> > diff --git a/drivers/mfd/fsl-imx8qxp-csr.c b/drivers/mfd/fsl-imx8qxp-csr.c
> > new file mode 100644
> > index 000000000000..3915d3d6ca65
> > --- /dev/null
> > +++ b/drivers/mfd/fsl-imx8qxp-csr.c
> > @@ -0,0 +1,53 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +
> > +/*
> > + * Copyright 2022 NXP
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/of_platform.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pm_runtime.h>
> > +
> > +static int imx8qxp_csr_probe(struct platform_device *pdev)
> > +{
> > +	int ret;
> > +
> > +	pm_runtime_enable(&pdev->dev);
> > +
> > +	ret = devm_of_platform_populate(&pdev->dev);
> 
> The use of this API does not constitute a MFD.
> 
> Please use "simple-mfd" instead.

simple-mfd devices have "ONLY_BUS" set in simple-pm-bus.c, so the
simple-pm-bus driver would not populate child devices of simple-mfd
devices.  Also, the simple-pm-bus driver would not enable runtime power
management for simple-mfd devices due to "ONLY_BUS", which means it
would not propagate power management operations from child devices of
simple-mfd devices to parent devices of simple-mfd devices.  That's why
a dedicated fsl-imx8qxp-csr driver is needed.   

Regards,
Liu Ying

[...]