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

From: Lee Jones <lee.jones@linaro.org>
To: Frank Rowand <frowand.list@gmail.com>
Cc: devicetree@vger.kernel.org, gregkh@linuxfoundation.org,
	broonie@kernel.org, michael@walle.cc,
	linux-kernel@vger.kernel.org, andy.shevchenko@gmail.com,
	robh+dt@kernel.org, linux-arm-kernel@lists.infradead.org,
	andriy.shevchenko@linux.intel.com, robin.murphy@arm.com,
	linus.walleij@linaro.org, linux@roeck-us.net
Subject: Re: [PATCH v2 1/3] mfd: core: Make a best effort attempt to match devices with the correct of_nodes
Date: Mon, 15 Jun 2020 10:26:44 +0100	[thread overview]
Message-ID: <20200615092644.GA2608702@dell> (raw)
In-Reply-To: <4b188fb5-6667-720d-46e1-6f103efe8966@gmail.com>

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"),
> 
> 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.

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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