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

Miquel Raynal
2023-03-08T18:07:38Z

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?

>
>
> >> config.reg_read = mtd_nvmem_reg_read;
> >> config.size = mtd->size;
> >> config.word_size = 1;
> >> @@ -891,6 +892,7 @@ static struct nvmem_device >> *mtd_otp_nvmem_register(struct mtd_info *mtd,
> >> config.name = kasprintf(GFP_KERNEL, "%s-%s", dev_name(&mtd->dev), >> compatible);
> >> config.id = NVMEM_DEVID_NONE;
> >> config.owner = THIS_MODULE;
> >> + config.use_fixed_of_cells = true;
> >> config.type = NVMEM_TYPE_OTP;
> >> config.root_only = true;
> >> config.ignore_wp = true;
> >> diff --git a/drivers/nvmem/apple-efuses.c >> b/drivers/nvmem/apple-efuses.c
> >> index 9b7c87102104..0119bac43b2c 100644
> >> --- a/drivers/nvmem/apple-efuses.c
> >> +++ b/drivers/nvmem/apple-efuses.c
> >> @@ -36,6 +36,7 @@ static int apple_efuses_probe(struct platform_device >> *pdev)
> >> struct resource *res;
> >> struct nvmem_config config = {
> >> .dev = &pdev->dev,
> >> + .use_fixed_of_cells = true,
> >> .read_only = true,
> >> .reg_read = apple_efuses_read,
> >> .stride = sizeof(u32),
> >> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> >> index 174ef3574e07..6783cd8478d7 100644
> >> --- a/drivers/nvmem/core.c
> >> +++ b/drivers/nvmem/core.c
> >> @@ -844,9 +844,11 @@ struct nvmem_device *nvmem_register(const struct >> nvmem_config *config)
> >> if (rval)
> >> goto err_remove_cells;
> >> >> - rval = nvmem_add_cells_from_of(nvmem);
> >> - if (rval)
> >> - goto err_remove_cells;
> >> + if (config->use_fixed_of_cells) {
> >> + rval = nvmem_add_cells_from_of(nvmem);
> >> + if (rval)
> >> + goto err_remove_cells;
> >> + }
> >> >> dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
> >> > > Thanks,
> > Miquèl

Thanks,
Miquèl