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

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

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.

> 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?

>  	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