linux-kernel - Re: [PATCH v3 01/13] mfd: Add i.MX generic mix support

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Date:   Thu, 30 Apr 2020 13:03:55 +0300
From:   Abel Vesa <abel.vesa@....com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Aisheng Dong <aisheng.dong@....com>,
        "arnd@...db.de" <arnd@...db.de>, Shawn Guo <shawnguo@...nel.org>,
        Peng Fan <peng.fan@....com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Anson Huang <anson.huang@....com>,
        Leonard Crestez <leonard.crestez@....com>,
        Jacky Bai <ping.bai@....com>, dl-linux-imx <linux-imx@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 01/13] mfd: Add i.MX generic mix support

On 20-04-24 07:27:27, Lee Jones wrote:
> On Thu, 23 Apr 2020, Aisheng Dong wrote:
> 
> > > From: Abel Vesa <abel.vesa@....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@....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@...20000 {
> >         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.
> 

OK, I'll do it in a single driver and single dts node.

But there might be an issue with the placement of this new driver.

drivers/clk/imx/ could be an option, but the driver will use a lot
of different APIs from different subsystems. Not the audiomix, but
the future mixes.

> -- 
> Lee Jones [李琼斯]
> Linaro Services Technical Lead
> Linaro.org │ Open source software for ARM SoCs
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