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

[Rafał Miłecki]

On 2023-03-08 19:06, Miquel Raynal wrote:
> Hi Rafał,
> 
> rafal at milecki.pl wrote on Wed, 08 Mar 2023 17:55:46 +0100:
> 
>> On 2023-03-08 17:34, Miquel Raynal wrote:
>> > Hi Rafał,
>> >
>> > zajec5 at gmail.com wrote on Fri, 24 Feb 2023 08:29:03 +0100:
>> >
>> >> From: Rafał Miłecki <rafal at 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 at milecki.pl>
>> >> [for drivers/nvmem/meson-{efuse,mx-efuse}.c]
>> >> Acked-by: Martin Blumenstingl <martin.blumenstingl at 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.