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

[Miquel Raynal <miquel.raynal@bootlin.com>]

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?

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.

Thanks, Miquèl

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