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Date:   Thu, 09 Mar 2023 09:39:54 +0100
From:   =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <rafal@milecki.pl>
To:     Miquel Raynal <miquel.raynal@bootlin.com>
Cc:     =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <zajec5@gmail.com>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
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        Neil Armstrong <neil.armstrong@linaro.org>,
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Subject: Re: [PATCH V2] nvmem: add explicit config option to read OF fixed
 cells
In-Reply-To: <20230309093415.2b1088c8@xps-13>
References: <20230224072903.20945-1-zajec5@gmail.com>
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On 2023-03-09 09:34, Miquel Raynal wrote:
> Hi Rafał,
> 
> zajec5@gmail.com wrote on Thu, 9 Mar 2023 07:56:05 +0100:
> 
>> 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
> 
> This is backwards. That's why layouts have been proposed: having
> a clear framework were the nvmem core should or should not play with
> the OF children nodes. If each binding is different, you end up with
> the mess we have today, where nobody knows how to properly
> populate the cells.
> 
> Anyway, it's not a big deal either, if the cells are empty we can
> easily check that and have *yet another* specific case in the core.
> 
>> 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()
> 
> Agreed. So what about config.ignore_of_children?
> - mtd sets this to !is_compatible(nvmem-cells)
> - nobody else touches it (the core don't try to parse the cell if it's
>   empty so U-Boot env driver works)

"ignore_of_children" would have opposite (reversed) meaning to the
"use_fixed_of_cells":
1. By default it would be 0 / false
2. By default NVMEM code would NOT ignore OF children nodes

That is what I actually *don't* want.

Having NVMEM core look for fixed cells in device node is undesirable.
I want that feature to be off by default. I want devices to have to
enable it explicitly only when it's needed.