From: Lee Jones <lee@kernel.org>
To: Liu Ying <victor.liu@nxp.com>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, shawnguo@kernel.org,
s.hauer@pengutronix.de, kernel@pengutronix.de,
festevam@gmail.com, linux-imx@nxp.com
Subject: Re: [PATCH RESEND] mfd: Add Freescale i.MX8qxp Control and Status Registers (CSR) module driver
Date: Mon, 7 Nov 2022 09:05:09 +0000 [thread overview]
Message-ID: <Y2jKRQ8VyauSfXmH@google.com> (raw)
In-Reply-To: <b7bcc99c006c91871f0518c1a132035d2a148f24.camel@nxp.com>
On Wed, 02 Nov 2022, Liu Ying wrote:
> Hi Lee,
>
> On Tue, 2022-11-01 at 13:53 +0800, Liu Ying wrote:
> > 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@nxp.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.
Right, simple-pm-bus will not populate child devices, because:
/*
* These are transparent bus devices (not simple-pm-bus matches) that
* have their child nodes populated automatically. So, don't need to
* do anything more. We only match with the device if this driver is
* the most specific match because we don't want to incorrectly bind to
* a device that has a more specific driver.
*/
So "simple-mfd" must be populated elsewhere i.e. drivers/of/platform.c.
> > 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.
This is more of an issue.
Why can't this device use "simple-pm-bus" to have support for both
auto-registration AND Runtime PM?
> One more point which might be overlooked - as mentioned in commit
> message, the CSR module is a child node of a simple power-managed
> bus(i.MX8qxp pixel link MSI bus), which means the child devices of the
> CSR module(as a simple-mfd device) won't be populated by
> of_platform_default_populate() from of_platform_default_populate_init()
> because "simple-pm-bus" is not listed in of_default_bus_match_table[]
> and hence recursion of of_platform_bus_create() will stop at the
> simple-pm-bus. This is also a reason why a dedicated fsl-imx8qxp-csr
> driver is needed to populated those child devices of the CSR module.
Not sure I know the semantics well enough (anymore) to get a
meaningful picture of what you're trying to explain, and I do not have
any suitable H/W here to mock-up a real-world test-bed / concept
demonstrator to debug this for you.
The long and the short of it is; we have a bunch of automatic
child-device-registering helpers in the kernel. One of the mechanisms
is bound to work for you if you structure your code appropriately.
Introducing an empty, meaningless driver, simply to call a single
function it not acceptable. Please make the infrastructure already
offered specifically to solve this category of issue work for your
use-case.
--
Lee Jones [李琼斯]
next prev parent reply other threads:[~2022-11-07 9:05 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-17 7:57 [PATCH RESEND] mfd: Add Freescale i.MX8qxp Control and Status Registers (CSR) module driver Liu Ying
2022-10-31 8:44 ` Liu Ying
2022-10-31 9:30 ` Lee Jones
2022-10-31 15:40 ` Lee Jones
2022-11-01 5:53 ` Liu Ying
2022-11-02 3:49 ` Liu Ying
2022-11-07 9:05 ` Lee Jones [this message]
2022-11-08 3:56 ` Liu Ying
2022-11-09 12:50 ` Ying Liu
2022-11-14 10:03 ` Lee Jones
2022-11-14 10:01 ` Lee Jones
2022-11-14 20:54 ` Rob Herring
2022-11-15 5:21 ` Liu Ying
2022-11-15 13:33 ` Rob Herring
2022-11-16 3:12 ` Liu Ying
2022-11-16 13:57 ` Lee Jones
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