Re: [PATCH RESEND] mfd: Add Freescale i.MX8qxp Control and Status Registers (CSR) module driver
From: Liu Ying <victor.liu@nxp.com>
Date: 2022-11-08 03:57:41
Also in:
lkml
Hi Lee, On Mon, 2022-11-07 at 09:05 +0000, Lee Jones wrote:
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.
/* * 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
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: --------------------------------8<------------------------------------ /kernel/linux/Documentation/devicetree/bindings/mfd/fsl,imx8qxp- csr.example.dtb: syscon@56221000: $nodename:0: 'syscon@56221000' does not match '^bus(@[0-9a-f]+)?$' From schema: /kernel/linux/Documentation/devicetree/bindings/bus/simple-pm-bus.yaml /kernel/linux/Documentation/devicetree/bindings/mfd/fsl,imx8qxp- csr.example.dtb: syscon@56221000: '#address-cells' is a required property From schema: /kernel/linux/Documentation/devicetree/bindings/bus/simple-pm-bus.yaml /kernel/linux/Documentation/devicetree/bindings/mfd/fsl,imx8qxp- csr.example.dtb: syscon@56221000: '#size-cells' is a required property From schema: /kernel/linux/Documentation/devicetree/bindings/bus/simple-pm-bus.yaml /kernel/linux/Documentation/devicetree/bindings/mfd/fsl,imx8qxp- csr.example.dtb: syscon@56221000: 'ranges' is a required property From schema: /kernel/linux/Documentation/devicetree/bindings/bus/simple-pm-bus.yaml --------------------------------8<------------------------------------ The error log basically complains two things: 1) The example nodename 'syscon@56221000' should match '^bus(@[0-9a-f]+)?$'. 2) Missing '#address-cells', '#size-cells' and 'ranges' properties as required by simple-pm-bus. Regarding 1), if I change 'syscon@56221000' to 'bus@56221000', then the below error comes along: --------------------------------8<------------------------------------ /kernel/linux/Documentation/devicetree/bindings/mfd/fsl,imx8qxp- csr.example.dtb: bus@56221000: $nodename:0: 'bus@56221000' does not match '^syscon@[0-9a-f]+$' From schema: /kernel/linux/Documentation/devicetree/bindings/mfd/fsl,imx8qxp- csr.yaml --------------------------------8<------------------------------------ So, it looks like "syscon" and "simple-pm-bus" can not be in compatbile string at the same time. Note that "syscon" is needed because other device nodes may reference the CSR module through a phandle, like the "fsl,imx8qxp-mipi-dphy" device. Regarding 2), I may try to add those required properties, but it would break the existing schemas of the child devices of the CSR module, like the "fsl,imx8qxp-ldb" device, because "reg" property is not allowed. So, it looks like the CSR module still should be simple-mfd device but not simple-pm-bus device, right?
quoted
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.
I understand you have no hardware to debug this directly. But, the example in dt-binding doc for the i.MX8qxp pixel link MSI bus(a simple- pm-bus) may give you a kinda full picture of what the relevant devices look like. I mentioned the patch set to add the MSI bus previously, however, you may find the binding doc directly here - https://lore.kernel.org/lkml/20221017074039.4181843-3-victor.liu@nxp.com/ (local)
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.
Yeah, I tried to not to introduce a new driver for the CSR module, but it seems that it is needed. Regards, Liu Ying _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel