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Date:   Wed, 08 Mar 2023 17:55:46 +0100
From:   =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <rafal@milecki.pl>
To:     Miquel Raynal <miquel.raynal@bootlin.com>
Cc:     =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <zajec5@gmail.com>,
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Subject: Re: [PATCH V2] nvmem: add explicit config option to read OF fixed
 cells
In-Reply-To: <20230308173256.3837b87b@xps-13>
References: <20230224072903.20945-1-zajec5@gmail.com>
 <20230308173256.3837b87b@xps-13>
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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