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