On Mon, Nov 7, 2022 at 9:58 PM Liu Ying [off-list ref] wrote:

Hi Lee,

On Mon, 2022-11-07 at 09:05 +0000, Lee Jones wrote:

quoted

On Wed, 02 Nov 2022, Liu Ying wrote:

quoted

Hi Lee,

On Tue, 2022-11-01 at 13:53 +0800, Liu Ying wrote:

quoted

Hi Lee,

On Mon, 2022-10-31 at 15:40 +0000, Lee Jones wrote:

quoted

On Mon, 17 Oct 2022, Liu Ying wrote:

quoted

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

[...]

quoted

quoted

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:

simple-pm-bus.c may populate child devices of simple-pm-bus devices
because "ONLY_BUS" is _not_ set for simple-pm-bus devices.

simple-pm-bus.c would _not_ populate child devices of simple-mfd
devices because "ONLY_BUS" is set for simple-mfd devices.

quoted

  /*
   * 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.

If simple-mfd device is a child device of one device listed in
of_default_bus_match_table[], then it may be populated by
drivers/of/platform.c.  But, in my case, simple-mfd device is a child
device of simple-pm-bus device(not listed in that table), so it will
not be populated by drivers/of/platform.c.  Instead,
drivers/bus/simple-pm-bus.c would populate the simple-mfd device.

quoted

quoted

quoted

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?

If I change the compatible string of the CSR module from
"fsl,imx8qxp-mipi-lvds-csr", "syscon", "simple-mfd"
to
"fsl,imx8qxp-mipi-lvds-csr", "syscon", "simple-pm-bus",
all devices I'm interested in are populated and all relevant drivers
can probe.  But, this change makes 'make dt_binding_check' for the
existing fsl,imx8qxp-csr.yaml fail:

As 'simple-bus' is for MMIO devices, so is 'simple-pm-bus' with the
addition of PM capabilities. That means you have registers defined
(reg), but you don't.

Either you have a block with mixed functions or you have separate
blocks. If the register space is all mixed together, then it is the
former and an MFD. Don't be designing your binding based on Linux
behavior.

Rob

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