From: Frank Rowand <frowand.list@gmail.com>
To: Lee Jones <lee.jones@linaro.org>
Cc: andy.shevchenko@gmail.com, michael@walle.cc, robh+dt@kernel.org,
broonie@kernel.org, devicetree@vger.kernel.org,
linus.walleij@linaro.org, linux@roeck-us.net,
andriy.shevchenko@linux.intel.com, robin.murphy@arm.com,
gregkh@linuxfoundation.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/3] mfd: core: Make a best effort attempt to match devices with the correct of_nodes
Date: Mon, 22 Jun 2020 09:35:50 -0500 [thread overview]
Message-ID: <f1e03639-a202-ab91-df38-453320d1ddeb@gmail.com> (raw)
In-Reply-To: <cd8952da-cc55-8087-b9f6-876417beb188@gmail.com>
On 2020-06-22 09:32, Frank Rowand wrote:
> On 2020-06-22 03:50, Lee Jones wrote:
>> 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?
>
> The OF_MFD_CELL() entry handles all of the existing .dts source files
> that only have one ab8500-pwm child nodes. So existing .dtb blobs
> continue to work.
>
> The OF_MFD_CELL_REG() entries will handle all of the new .dts source
> files that will have up to 3 ab8500-pwm child nodes.
>
> Compatibility is maintained for existing .dtb files. A new kernel
> version with the changes will support new .dtb files that contain
> multiple ab8500-pwm child nodes.
>
>>
>>> 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?
>
> Based on reading the patch description, I expected some extra code to try
> to handle the case where the compatible in more than one struct mfd_cell
> entry is "stericsson,ab8500-pwm" and there are multiple ab8500-pwm child
> nodes.
>
> Looking at the actual code (which I had not done before), I see that the
> "best effort attempt to match" is keeping a list of child nodes that
> have already been used (mfd_of_node_list) and avoiding re-use of such
> nodes. This allows an invalid .dtb (one with multple "stericsson,ab8500-pwm"
> child nodes) to possibly be assigned unique child nodes for multiple
> struct mfd_cell entries to be "stericsson,ab8500-pwm".
struct mfd_cell entries that each have the same compatible value
"stericsson,ab8500-pwm".
Some day I'll learn how to speak my native language. :-)
-Frank
>
> So it is confusing for me to call that "fallback code". It really is
> "best effort attempt to match" for a broken .dtb code.
>
> There should be no best effort for a broken .dtb. The broken .dtb should
> instead result in an error.
>
> -Frank
>
>>
>>>> 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.
>>>>
>>>
>>
>
next prev parent reply other threads:[~2020-06-22 14:35 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-11 19:10 [PATCH v2 1/3] mfd: core: Make a best effort attempt to match devices with the correct of_nodes Lee Jones
2020-06-11 19:10 ` [PATCH v2 2/3] mfd: core: Fix formatting of MFD helpers Lee Jones
2020-06-12 12:27 ` Frank Rowand
2020-06-11 19:10 ` [PATCH v2 3/3] mfd: core: Add OF_MFD_CELL_REG() helper Lee Jones
2020-06-12 12:28 ` Frank Rowand
2020-06-12 12:26 ` [PATCH v2 1/3] mfd: core: Make a best effort attempt to match devices with the correct of_nodes Frank Rowand
2020-06-15 1:19 ` Frank Rowand
2020-06-15 9:26 ` Lee Jones
2020-06-18 17:34 ` Frank Rowand
2020-06-22 8:50 ` Lee Jones
2020-06-22 14:32 ` Frank Rowand
2020-06-22 14:35 ` Frank Rowand [this message]
2020-06-22 15:10 ` Lee Jones
2020-06-22 18:01 ` Frank Rowand
2020-06-22 18:04 ` Frank Rowand
2020-06-22 19:11 ` Lee Jones
2020-06-22 22:23 ` Frank Rowand
2020-06-23 1:17 ` Frank Rowand
2020-06-23 1:37 ` Frank Rowand
2020-06-23 6:47 ` Lee Jones
2020-06-23 17:55 ` Frank Rowand
2020-06-23 19:59 ` Lee Jones
2020-06-23 22:33 ` Frank Rowand
2020-06-24 7:46 ` Lee Jones
2020-06-24 15:51 ` Frank Rowand
2020-06-24 16:14 ` Lee Jones
2020-06-24 16:25 ` Frank Rowand
2020-06-22 8:09 ` Lee Jones
2020-06-22 16:09 ` Frank Rowand
2020-06-22 16:53 ` Lee Jones
2020-06-23 22:21 ` Frank Rowand
2020-06-24 6:45 ` Lee Jones
2020-06-23 23:03 ` Frank Rowand
2020-06-24 6:41 ` Lee Jones
2020-06-24 7:47 ` Michael Walle
2020-06-24 8:23 ` Lee Jones
2020-06-24 9:19 ` Michael Walle
2020-06-24 11:24 ` Lee Jones
2020-06-11 19:12 Lee Jones
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