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

Rafał Miłecki
2023-03-08T20:33:26Z

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).

>> 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

>> 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