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    SubjectRe: [PATCH v3 01/13] mfd: Add i.MX generic mix support
    On Thu, 23 Apr 2020, Aisheng Dong wrote:

    > > From: Abel Vesa <abel.vesa@nxp.com>
    > > Sent: Wednesday, April 22, 2020 5:19 PM
    > > On 20-04-17 09:07:47, Lee Jones wrote:
    > > > On Wed, 15 Apr 2020, Abel Vesa wrote:
    > > >
    > > > > Some of the i.MX SoCs have a IP for interfacing the dedicated IPs
    > > > > with clocks, resets and interrupts, plus some other specific control registers.
    > > > > To allow the functionality to be split between drivers, this MFD
    > > > > driver is added that has only two purposes: register the devices and
    > > > > map the entire register addresses. Everything else is left to the
    > > > > dedicated drivers that will bind to the registered devices.
    > > > >
    > > > > Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
    > > > > ---
    > > > > drivers/mfd/Kconfig | 11 +++++++++++
    > > > > drivers/mfd/Makefile | 1 +
    > > > > drivers/mfd/imx-mix.c | 48
    > > > > ++++++++++++++++++++++++++++++++++++++++++++++++
    > > > > 3 files changed, 60 insertions(+)
    > > > > create mode 100644 drivers/mfd/imx-mix.c
    > > >
    > > > For completeness - Arnd's reply to this patch:
    > > >
    > >
    > > I'm replying here to Arnd's reply.
    > >
    > > I'm trying to give here a whole picture of the entire problem while the
    > > documentation for i.MX8MP is _not yet_ public.
    > >
    > > Historically, each IP would have its own enclosure for all the related GPRs.
    > > Starting with i.MX8MP some GPRs (and some subparts) from the IP were placed
    > > inside these mixes.
    > >
    > > Audiomix for example, has multiple SAIs, a PLL, and some reset bits for EARC
    > > and some GPRs for AudioDSP. This means that i.MX8MP has 7 SAIs, 1 EARC and
    > > 1 AudioDSP.
    > > Future platforms might have different numbers of SAIs, EARCs or AudioDSPs.
    > > The PLL can't be placed in one of those SAIs and it was placed in audiomix.
    > > The i.MX8MP has at least 4 of these mixes.
    > >
    > > Now, the commonalities between all mixes are:
    > > - have their own power domains
    > > - driven by dedicated clock slice
    > > - contain clocks and resets
    > > - some very subsystem specific GPRs
    > >
    > > Knowing that each mix has its own power domain, AFAICT, it needs to be
    > > registered as a single device. Considering that it can have clocks (audiomix has
    > > gates, muxes and plls), I believe that needs a clock driver, even more so since the
    > > muxes need their parents from the platform clock driver. Same principle applies
    > > to reset bits. The subsystem specific GPRs can be registered as syscon devices
    > > and taken care of by its counterpart IP (e.g. the AudioDSP specific regs would be
    > > taken care of by the DSP driver, if there is one).
    > >
    > > Now based on all of the above, by using MFD we take care of the power domain
    > > control for the entire mix, plus, the MFD doesn't have any kind of functionality
    > > by its own, relying on its children devices that are populated based on what is in
    > > the mix MFD devicetree node.
    > >
    >
    > How about doing like this which maybe can address Arnd's concerns?
    > audiomix: audiomix@30e20000 {
    > compatible = "fsl,imx8mp-audiomix", "syscon";
    > reg = <0x30e20000 xxx>,
    > <0x30e20xxx xxx>;
    > reg-names = "audio", "reset", "...";
    > #clock-cells = <1>;
    > #reset-cells = <1>;
    > power-domains = <&audiomix_pd>;
    > }
    >
    > That means we have one combo driver registering two controllers (clk/reset), both use
    > the same power domain as audiomix.
    > And it can be easily extended to support more services provided by audiomix over syscon
    > if needed.
    > Then the 'dummy' MDF driver is not needed anymore.
    >
    > Jones & Arnd,
    > How do you think?

    Sounds okay in principle. Anything that prevents the existence of a
    dummy (a.k.a. pointless) MFD must be seen as a positive move.

    --
    Lee Jones [李琼斯]
    Linaro Services Technical Lead
    Linaro.org │ Open source software for ARM SoCs
    Follow Linaro: Facebook | Twitter | Blog

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