Re: [PATCH] driver: bus: simple-pm-bus: Add Freescale i.MX8qm/qxp CSR compatible strings

[Liu Ying <victor.liu@nxp.com>]

On Sun, 2023-01-29 at 11:49 +0100, Krzysztof Kozlowski wrote:
> On 29/01/2023 09:13, Liu Ying wrote:
> > On Thu, 2023-01-26 at 13:45 +0100, Krzysztof Kozlowski wrote:
> > > On 26/01/2023 03:54, Liu Ying wrote:
> > > > On Wed, 2023-01-25 at 10:05 +0100, Geert Uytterhoeven wrote:
> > > > > Hi Liu,
> > > > 
> > > > Hi Geert,
> > > > 
> > > > > 
> > > > > On Wed, Jan 25, 2023 at 9:31 AM Liu Ying <victor.liu@nxp.com>
> > > > > wrote:
> > > > > > Freescale i.MX8qm/qxp CSR module matches with what the
> > > > > > simple
> > > > > > power
> > > > > > managed bus driver does, considering it needs an IPG clock
> > > > > > to
> > > > > > be
> > > > > > enabled before accessing it's child devices, the child
> > > > > > devices
> > > > > > need
> > > > > > to be populated by the CSR module and the child devices'
> > > > > > power
> > > > > > management operations need to be propagated to their parent
> > > > > > devices.
> > > > > > Add the CSR module's compatible strings to
> > > > > > simple_pm_bus_of_match[]
> > > > > > table to support the CSR module.
> > > > > > 
> > > > > > Suggested-by: Rob Herring <robh@kernel.org>
> > > > > > Suggested-by: Lee Jones <lee@kernel.org>
> > > > > > Signed-off-by: Liu Ying <victor.liu@nxp.com>
> > > > > 
> > > > > Thanks for your patch!
> > > > 
> > > > Thanks for your review!
> > > > 
> > > > > 
> > > > > > ---
> > > > > > The CSR module's dt-binding documentation can be found at
> > > > > > Documentation/devicetree/bindings/mfd/fsl,imx8qxp-csr.yaml.
> > > > > > 
> > > > > > Suggested by Rob and Lee in this thread:
> > > > > > 
> > > > 
> > > > 
> > 
> > 
https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.kernel.org%2Fproject%2Flinux-arm-kernel%2Fpatch%2F20221017075702.4182846-1-victor.liu%40nxp.com%2F&data=05%7C01%7Cvictor.liu%40nxp.com%7C58af8a86f0134b6bde3408db01e68522%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C638105861813147063%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=mHv%2BTAHMAR8coxDmXucoMbxv%2BuMEdHWHTyLz16OUY50%3D&reserved=0
> > > > > > 
> > > > > >  drivers/bus/simple-pm-bus.c | 2 ++
> > > > > >  1 file changed, 2 insertions(+)
> > > > > > 
> > > > > > diff --git a/drivers/bus/simple-pm-bus.c
> > > > > > b/drivers/bus/simple-
> > > > > > pm-
> > > > > > bus.c
> > > > > > index 7afe1947e1c0..4a7575afe6c6 100644
> > > > > > --- a/drivers/bus/simple-pm-bus.c
> > > > > > +++ b/drivers/bus/simple-pm-bus.c
> > > > > > @@ -120,6 +120,8 @@ static const struct of_device_id
> > > > > > simple_pm_bus_of_match[] = {
> > > > > >         { .compatible = "simple-mfd",   .data = ONLY_BUS },
> > > > > >         { .compatible = "isa",          .data = ONLY_BUS },
> > > > > >         { .compatible = "arm,amba-bus", .data = ONLY_BUS },
> > > > > > +       { .compatible = "fsl,imx8qm-lvds-csr", },
> > > > > > +       { .compatible = "fsl,imx8qxp-mipi-lvds-csr", },
> > > > > 
> > > > > I did read the thread linked above, and I still think you
> > > > > should
> > > > > just
> > > > > add "simple-pm-bus" to the compatible value in DTS, so no
> > > > > driver
> > > > > change
> > > > > is needed, cfr.
> > > > > Documentation/devicetree/bindings/bus/renesas,bsc.yaml.
> > > 
> > > I don't think we want to start putting specific compatibles here.
> > > We
> > > don't do it for simple-mfd, syscon and simple-bus, so neither
> > > should
> > > we
> > > do it here.
> > > 
> > > > 
> > > > This means that i.MX8qm/qxp CSR module dt-binding documentation
> > > > needs
> > > > to be changed.  I'd like to know how Rob and Krzysztof think
> > > > about
> > > > that.
> > > 
> > > The fsl,imx8qxp-csr.yaml bindings are broken anyway... You have
> > > device
> > > specific bindings for non-simple device but use simple-mfd. You
> > > cannot.
> > > simple-mfd means it is simple and none of the resources are
> > > needed
> > > for
> > > children, but that binding contradicts it.
> > > 
> > > Now you kind of try to extend it even more make it more and more
> > > broken.
> > > 
> > > Rework the bindings keeping them backwards compatible. The
> > > combination
> > > with simple-mfd should be deprecated and you can add whatever is
> > > needed
> > > for a proper setup.
> > 
> > I did try to rework the bindings and make the combination with
> > simple-
> > mfd deprecated. However, it reminds me the problem that "simple-pm-
> > bus" 
> > and "syscon" can not be in compatible string at the same time,
> > otherwise, nodename should match '^syscon@[0-9a-f]+$' and '^bus@[0-
> > 9a-
> > f]+$' at the same time. I mentioned the problem in the same
> > thread[1]
> > where Rob and Lee suggest to go with this patch. "syscon" is needed
> > since i.MX8qxp MIPI DSI/LVDS combo PHY node references the CSR
> > module
> > through a phandle, so dropping/deprecating "syscon" is a no-go. 
> > 
> > Also, as Rob mentioned in [1] "if register space is all mixed
> > together,
> > then it is the former and an MFD", I think the CSR module should
> > fall
> > into the simple-mfd category. 
> 
> You are now mixing MFD with simple-mfd. If you have clocks there or
> any
> other resources, it's not simple-mfd anymore.

I may try to make the combination with simple-mfd deprecated and add
another combination with i.MX8qm/qxp CSR compatible strings and syscon
only. Then, it will be a MFD, not simple-mfd.

> 
> > Take i.MX8qxp MIPI DSI/LVDS CSR module as
> > an example, child device pxl2dpi register offset is 0x40, while
> > child
> > device ldb register offsets are 0x20 and 0xe0.
> > 
> > Geert, Krzysztof, can you please consider to keep this patch as-is,
> > since it seems that there is no other option?
> 
> There are other options, why do you say there is no? Making it proper
> binding/driver for its children without abusing simple bindings.

I don't quite understand your comment here, sorry. Here are the 3
options I know:

1) Add a new MFD driver for the CSR module
I sent out a MFD driver[1] for the CSR module for review, but Rob and
Lee provided comments there and suggested to use this patch.

2) Use "simple-pm-bus" compatible string in the CSR module's compatbile
property
As mentioned before, "simple-pm-bus" contradicts with "syscon".

3) Add the CSR module's specific compatible strings in
simple_pm_bus_of_match[]
This is what this patch does and suggested by Rob and Lee.

Looks like 3) is the only feasible option.

Geert, Krzysztof, any objections to keep this patch as-is?

[1] 
https://patchwork.kernel.org/project/linux-arm-kernel/patch/20221017075702.4182846-1-victor.liu@nxp.com/


Regards,
Liu Ying


> Simple
> bindings are for simple cases and this turns out not the simple case.
> 
> Best regards,
> Krzysztof
>