Messages in this thread | | | Date | Wed, 16 Nov 2022 13:57:04 +0000 | From | Lee Jones <> | Subject | Re: [PATCH RESEND] mfd: Add Freescale i.MX8qxp Control and Status Registers (CSR) module driver |
| |
On Wed, 16 Nov 2022, Liu Ying wrote:
> On Tue, 2022-11-15 at 07:33 -0600, Rob Herring wrote: > > On Mon, Nov 14, 2022 at 11:22 PM Liu Ying <victor.liu@nxp.com> wrote: > > > On Mon, 2022-11-14 at 14:54 -0600, Rob Herring wrote: > > > > On Mon, Nov 7, 2022 at 9:58 PM Liu Ying <victor.liu@nxp.com> wrote: > > > > > Hi Lee, > > > > > > > > > > On Mon, 2022-11-07 at 09:05 +0000, Lee Jones wrote: > > > > > > 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: > > > > > > > > > > > > > [...] > > > > > > > > > > > > + 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. > > > > > > > > > > > > > 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. > > > > > > Thanks for clarifying how to differetiate MFD and 'simple-bus'/'simple- > > > pm-bus'. I would say the register space of the CSR module is mixed > > > together, e.g., LVDS PHY child device has a register offset 0x00, > > > PXL2DPI child device has a register offset 0x40 and LDB child device > > > has register offsets 0x20 and 0xe0 in i.MX8qxp MIPI DSI/LVDS combo > > > subsystem CSR module register space. So, it appears to be a MFD. > > > > > > Lee, what do you think? If it is indeed an MFD, a new MFD driver for > > > the CSR module is needed then. > > > > There already exists a driver which does what you need, so why create > > a 2nd one? Just add the "fsl,imx8qxp-mipi-lvds-csr" compatible to the > > simple-pm-bus match table and don't set ONLY_BUS. Isn't that enough? > > Adding "fsl,imx8qxp-mipi-lvds-csr" and "fsl,imx8qm-lvds-csr" compatible > strings to the simple-pm-bus match table does work, but it tends to > make people think the CSR module is a bus instead of a MFD.
MFDs don't exist. They're a figment of our imagination.
If you want PM enabled and wish for your child devices to be auto-magically registered for you, simple-pm-bus is what you need.
> It's kinka > straightforward if a MFD device driver lives in drivers/mfd directory. > However, since "simple-mfd" compatible is also in that match table, I > would add the CSR module's compatible strings to that match table if no > objections.
Fine by me if it saves authoring a pointless driver.
-- Lee Jones [李琼斯]
| |