Re: [PATCH V2] nvmem: add explicit config option to read OF fixed cells

["Rafał Miłecki" <zajec5@gmail.com>]

On 8.03.2023 19:31, Miquel Raynal wrote:
> Hi Rafał,
> 
> rafal@milecki.pl wrote on Wed, 08 Mar 2023 19:12:32 +0100:
> 
>> On 2023-03-08 19:06, Miquel Raynal wrote:
>>> Hi Rafał,
>>>
>>> rafal@milecki.pl wrote on Wed, 08 Mar 2023 17:55:46 +0100:
>>>    
>>>> On 2023-03-08 17:34, Miquel Raynal wrote:
>>>>> Hi Rafał,
>>>>>
>>>>> zajec5@gmail.com wrote on Fri, 24 Feb 2023 08:29:03 +0100:
>>>>>   
>>>>>> From: Rafał Miłecki <rafal@milecki.pl>
>>>>>>>> NVMEM subsystem looks for fixed NVMEM cells (specified in DT) by
>>>>>> default. This behaviour made sense in early days before adding support
>>>>>> for dynamic cells.
>>>>>>>> With every new supported NVMEM device with dynamic cells current
>>>>>> behaviour becomes non-optimal. It results in unneeded iterating over >> DT
>>>>>> nodes and may result in false discovery of cells (depending on used DT
>>>>>> properties).
>>>>>>>> This behaviour has actually caused a problem already with the MTD
>>>>>> subsystem. MTD subpartitions were incorrectly treated as NVMEM cells.
>>>>>
>>>>> That's true, but I expect this to be really MTD specific.
>>>>>
>>>>> A concrete proposal below.
>>>>>   
>>>>>> Also with upcoming support for NVMEM layouts no new binding or driver
>>>>>> should support fixed cells defined in device node.
>>>>>
>>>>> I'm not sure I agree with this statement. We are not preventing new
>>>>> binding/driver to use fixed cells, or...? We offer a new way to expose
>>>>> nvmem cells with another way than "fixed-offset" and "fixed-size" OF
>>>>> nodes.
>>>>>>   From what I understood all new NVMEM bindings should have cells >> defined
>>>> in the nvmem-layout { } node. That's what I mean by saying they should
>>>> not be defined in device node (but its "nvmem-layout" instead).
>>>
>>> Layouts are just another possibility, either you user the nvmem-cells
>>> compatible and produce nvmem cells with fixed OF nodes, or you use the
>>> nvmem-layout container. I don't think all new bindings should have
>>> cells in layouts. It depends if the content is static or not.
>>>    
>>>>>> Solve this by modifying drivers for bindings that support specifying
>>>>>> fixed NVMEM cells in DT. Make them explicitly tell NVMEM subsystem to
>>>>>> read cells from DT.
>>>>>>>> It wasn't clear (to me) if rtc and w1 code actually uses fixed cells. >> I
>>>>>> enabled them to don't risk any breakage.
>>>>>>>> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
>>>>>> [for drivers/nvmem/meson-{efuse,mx-efuse}.c]
>>>>>> Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
>>>>>> ---
>>>>>> V2: Fix stm32-romem.c typo breaking its compilation
>>>>>>      Pick Martin's Acked-by
>>>>>>      Add paragraph about layouts deprecating use_fixed_of_cells
>>>>>> ---
>>>>>>   drivers/mtd/mtdcore.c          | 2 ++
>>>>>>   drivers/nvmem/apple-efuses.c   | 1 +
>>>>>>   drivers/nvmem/core.c           | 8 +++++---
>>>>>>   drivers/nvmem/imx-ocotp-scu.c  | 1 +
>>>>>>   drivers/nvmem/imx-ocotp.c      | 1 +
>>>>>>   drivers/nvmem/meson-efuse.c    | 1 +
>>>>>>   drivers/nvmem/meson-mx-efuse.c | 1 +
>>>>>>   drivers/nvmem/microchip-otpc.c | 1 +
>>>>>>   drivers/nvmem/mtk-efuse.c      | 1 +
>>>>>>   drivers/nvmem/qcom-spmi-sdam.c | 1 +
>>>>>>   drivers/nvmem/qfprom.c         | 1 +
>>>>>>   drivers/nvmem/rave-sp-eeprom.c | 1 +
>>>>>>   drivers/nvmem/rockchip-efuse.c | 1 +
>>>>>>   drivers/nvmem/sc27xx-efuse.c   | 1 +
>>>>>>   drivers/nvmem/sprd-efuse.c     | 1 +
>>>>>>   drivers/nvmem/stm32-romem.c    | 1 +
>>>>>>   drivers/nvmem/sunplus-ocotp.c  | 1 +
>>>>>>   drivers/nvmem/sunxi_sid.c      | 1 +
>>>>>>   drivers/nvmem/uniphier-efuse.c | 1 +
>>>>>>   drivers/nvmem/zynqmp_nvmem.c   | 1 +
>>>>>>   drivers/rtc/nvmem.c            | 1 +
>>>>>>   drivers/w1/slaves/w1_ds250x.c  | 1 +
>>>>>>   include/linux/nvmem-provider.h | 2 ++
>>>>>>   23 files changed, 29 insertions(+), 3 deletions(-)
>>>>>>>> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
>>>>>> index 0feacb9fbdac..1bb479c0f758 100644
>>>>>> --- a/drivers/mtd/mtdcore.c
>>>>>> +++ b/drivers/mtd/mtdcore.c
>>>>>> @@ -523,6 +523,7 @@ static int mtd_nvmem_add(struct mtd_info *mtd)
>>>>>>   	config.dev = &mtd->dev;
>>>>>>   	config.name = dev_name(&mtd->dev);
>>>>>>   	config.owner = THIS_MODULE;
>>>>>> +	config.use_fixed_of_cells = of_device_is_compatible(node, >> "nvmem-cells");
>>>>>
>>>>> I am wondering how mtd specific this is? For me all OF nodes containing
>>>>> the nvmem-cells compatible should be treated as cells providers and
>>>>> populate nvmem cells as for each children.
>>>>>
>>>>> Why don't we just check for this compatible to be present? in
>>>>> nvmem_add_cells_from_of() ? And if not we just skip the operation.
>>>>>
>>>>> This way we still follow the bindings (even though using nvmem-cells in
>>>>> the compatible property to require cells population was a mistake in
>>>>> the first place, as discussed in the devlink thread recently) but there
>>>>> is no need for a per-driver config option?
>>>>>> This isn't mtd specific. Please check this patch for all occurrences >> of
>>>> the:
>>>> use_fixed_of_cells = true
>>>>>> The very first one: drivers/nvmem/apple-efuses.c driver for the
>>>> "apple,efuses" binding. That binding supports fixed OF cells, see:
>>>> Documentation/devicetree/bindings/nvmem/apple,efuses.yaml
>>>
>>> I'm saying: based on what has been enforced so far, I would expect all
>>> fixed cell providers to come with nvmem-cells as compatible, no?
>>>
>>> If that's the case we could use that as a common denominator?
>>
>> Sorry, I don't get it. Have you checked
>> Documentation/devicetree/bindings/nvmem/apple,efuses.yaml
>> ?
>>
>> It's a NVMEM provied binding with fixed cells that doesn't use
>> nvmem-cells as compatible. There are many more.
> 
> Oh yeah you're right, I'm mixing things. Well I guess you're right
> then, it's such a mess, we have to tell the core the parsing method.
> 
> So maybe another question: do we have other situations than mtd which
> sometimes expect the nvmem core to parse the OF nodes to populate cells,
> and sometimes not?

I'm not aware of that. Please also check my patch. The only case I set
"use_fixed_of_cells" conditionally is mtd code. In other cases it's
hardcoded to "true".


> Also, what about "of_children_are_cells" ? Because actually in most
> cases it's a "fixed of cell", so I don't find the current naming
> descriptive enough for something so touchy.

That would be just incorrect because this new config property
("use_fixed_of_cells") is only about FIXED cells.

There are cases of OF children being cells but NOT being fixed cells.
They should NOT be parsed by the nvmem_add_cells_from_of().

Example:
a607a850ba1f ("dt-bindings: nvmem: u-boot,env: add basic NVMEM cells")
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a607a850ba1fa966cbb035544c1588e24a6307df

So that would result in U-Boot env:
1. Having OF children nodes being cells
2. Setting "of_children_are_cells" to false (counter-intuitive) to avoid nvmem_add_cells_from_of()

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