linux-kernel - Re: [PATCH v2 1/3] mfd: core: Make a best effort attempt to match devices with the correct of

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Message-ID: <20200622085009.GP954398@dell>
Date:   Mon, 22 Jun 2020 09:50:09 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     andy.shevchenko@...il.com, michael@...le.cc, robh+dt@...nel.org,
        broonie@...nel.org, devicetree@...r.kernel.org,
        linus.walleij@...aro.org, linux@...ck-us.net,
        andriy.shevchenko@...ux.intel.com, robin.murphy@....com,
        gregkh@...uxfoundation.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] mfd: core: Make a best effort attempt to match
 devices with the correct of_nodes

On Thu, 18 Jun 2020, Frank Rowand wrote:

> On 2020-06-15 04:26, Lee Jones wrote:
> > On Sun, 14 Jun 2020, Frank Rowand wrote:
> > 
> >> Hi Lee,
> >>
> >> I'm looking at 5.8-rc1.
> >>
> >> The only use of OF_MFD_CELL() where the same compatible is specified
> >> for multiple elements of a struct mfd_cell array is for compatible
> >> "stericsson,ab8500-pwm" in drivers/mfd/ab8500-core.c:
> >>
> >>         OF_MFD_CELL("ab8500-pwm",
> >>                     NULL, NULL, 0, 1, "stericsson,ab8500-pwm"),
> >>         OF_MFD_CELL("ab8500-pwm",
> >>                     NULL, NULL, 0, 2, "stericsson,ab8500-pwm"),
> >>         OF_MFD_CELL("ab8500-pwm",
> >>                     NULL, NULL, 0, 3, "stericsson,ab8500-pwm"),
> 
>          OF_MFD_CELL("ab8500-pwm",
>                      NULL, NULL, 0, 0, "stericsson,ab8500-pwm"),
> 
>          OF_MFD_CELL_REG("ab8500-pwm-mc",
>                          NULL, NULL, 0, 0, "stericsson,ab8500-pwm", 0),
>          OF_MFD_CELL_REG("ab8500-pwm-mc",
>                          NULL, NULL, 0, 1, "stericsson,ab8500-pwm", 1),
>          OF_MFD_CELL_REG("ab8500-pwm-mc",
>                          NULL, NULL, 0, 2, "stericsson,ab8500-pwm", 2),
> 
> >>
> >> The only .dts or .dtsi files where I see compatible "stericsson,ab8500-pwm"
> >> are:
> >>
> >>    arch/arm/boot/dts/ste-ab8500.dtsi
> >>    arch/arm/boot/dts/ste-ab8505.dtsi
> >>
> >> These two .dtsi files only have a single node with this compatible.
> >> Chasing back to .dts and .dtsi files that include these two .dtsi
> >> files, I see no case where there are multiple nodes with this
> >> compatible.
> >>
> >> So it looks to me like there is no .dts in mainline that is providing
> >> the three "stericsson,ab8500-pwm" nodes that drivers/mfd/ab8500-core.c
> >> is expecting.  No case that there are multiple mfd child nodes where
> >> mfd_add_device() would assign the first of n child nodes with the
> >> same compatible to multiple devices.
> >>
> >> So it appears to me that drivers/mfd/ab8500-core.c is currently broken.
> >> Am I missing something here?
> >>
> >> If I am correct, then either drivers/mfd/ab8500-core.c or
> >> ste-ab8500.dtsi and ste-ab8505.dtsi need to be fixed.
> > 
> > Your analysis is correct.
> 
> OK, if I'm not overlooking anything, that is good news.
> 
> Existing .dts source files only have one "ab8500-pwm" child.  They already
> work correcly.
> 
> Create a new compatible for the case of multiple children.  In my example
> I will add "-mc" (multiple children) to the existing compatible.  There
> is likely a better name, but this lets me provide an example.
> 
> Modify drivers/mfd/ab8500-core.c to use the new compatible, and new .dts
> source files with multiple children use the new compatible:
> 
>          OF_MFD_CELL("ab8500-pwm",
>                      NULL, NULL, 0, 0, "stericsson,ab8500-pwm"),
> 
>          OF_MFD_CELL_REG("ab8500-pwm-mc",
>                          NULL, NULL, 0, 0, "stericsson,ab8500-pwm", 0),
>          OF_MFD_CELL_REG("ab8500-pwm-mc",
>                          NULL, NULL, 0, 1, "stericsson,ab8500-pwm", 1),
>          OF_MFD_CELL_REG("ab8500-pwm-mc",
>                          NULL, NULL, 0, 2, "stericsson,ab8500-pwm", 2),
> 
> The "OF_MFD_CELL" entry is the existing entry, which will handle current
> .dts source files.  The new "OF_MFD_CELL_REG" entries will handle new
> .dts source files.

Sorry, but I'm not sure what the above exercise is supposed to solve.

Could you explain it for me please?

> And of course the patch that creates OF_MFD_CELL_REG() needs to precede
> this change.
> 
> I would remove the fallback code in the existing patch that tries to
> handle an incorrect binding.  Just error out if the binding is not
> used properly.

What fallback code?

> > Although it's not "broken", it just works when it really shouldn't.
> > 
> > I will be fixing the 'ab8500-pwm' case in due course.
> > 
> >> Moving forward, your proposed OF_MFD_CELL_REG() method seems a good
> >> approach (I have not completely read the actual code in the patch yet
> >> though).
> > 
> > Thanks.
> > 
> 

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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