diff mbox series

nvmem: add explicit config option to read OF fixed cells

Message ID 20230221145021.31993-1-zajec5@gmail.com (mailing list archive)
State Superseded
Headers show
Series nvmem: add explicit config option to read OF fixed cells | expand

Commit Message

Rafał Miłecki Feb. 21, 2023, 2:50 p.m. UTC
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.

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>
---
 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(-)

Comments

Martin Blumenstingl Feb. 21, 2023, 9:38 p.m. UTC | #1
Hello Rafał,

On Tue, Feb 21, 2023 at 3:50 PM Rafał Miłecki <zajec5@gmail.com> wrote:
>
> 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).
I am not familiar with the recent changes around dynamic cells.
Is there any discussion/summary that I can read to get up to speed?

My main thought is: if there are many "fixed OF cells" implementations
and only a few "dynamic" ones - does it make sense to flip the logic
and introduce a new "use_dynamic_of_cells" flag instead?


Best regards,
Martin
Rafał Miłecki Feb. 21, 2023, 10:29 p.m. UTC | #2
On 21.02.2023 22:38, Martin Blumenstingl wrote:
> On Tue, Feb 21, 2023 at 3:50 PM Rafał Miłecki <zajec5@gmail.com> wrote:
>>
>> 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).
> I am not familiar with the recent changes around dynamic cells.
> Is there any discussion/summary that I can read to get up to speed?

Some NVMEM devices don't store specific data at hardcoded offsets. For
such devices we have drivers (to become: layouts) that parse their magic
content. They discover cells and register them and provide matching with
proper DT nodes.

For bindings see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=084973e944bec21804f8afb0515b25434438699a
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a607a850ba1fa966cbb035544c1588e24a6307df

For example driver see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6e977eaa8280e957b87904b536661550f2a6b3e8
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=207775f7e17b8fd0426a2ac4a5b81e4e1d71849e

For usage see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c8442f0fb09ca3d842b9b23d1d0650f649fd10f8


> My main thought is: if there are many "fixed OF cells" implementations
> and only a few "dynamic" ones - does it make sense to flip the logic
> and introduce a new "use_dynamic_of_cells" flag instead?

The problem is that there are more cases than just two. We can have:
1. No cells at all
2. Fixed cells in DT
3. Dynamic cells with references in DT
4. Driver specified cells (specified within config)
5. Cells defined in a global table

So we need to reference DT cells explicitly (we can't just confirm /
deny *dynamic* cells).

Another solution would be to have "no_fixed_of_cells" but:

1. Personally I think negation is less clear / easy to follow

2. There may be actually more drivers with no fixed cells.
I think I modified 18 drivers. It seems devm_nvmem_register() is
referenced in 44 places. Few of them may be not actual users but it
still seems to be about equal.
Martin Blumenstingl Feb. 22, 2023, 9:14 p.m. UTC | #3
Hello Rafał,

On Tue, Feb 21, 2023 at 11:29 PM Rafał Miłecki <zajec5@gmail.com> wrote:
[...]
> > I am not familiar with the recent changes around dynamic cells.
> > Is there any discussion/summary that I can read to get up to speed?
>
> Some NVMEM devices don't store specific data at hardcoded offsets. For
> such devices we have drivers (to become: layouts) that parse their magic
> content. They discover cells and register them and provide matching with
> proper DT nodes.
>
> For bindings see:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=084973e944bec21804f8afb0515b25434438699a
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a607a850ba1fa966cbb035544c1588e24a6307df
>
> For example driver see:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6e977eaa8280e957b87904b536661550f2a6b3e8
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=207775f7e17b8fd0426a2ac4a5b81e4e1d71849e
>
> For usage see:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c8442f0fb09ca3d842b9b23d1d0650f649fd10f8
Thanks, that makes things clearer for me!

> > My main thought is: if there are many "fixed OF cells" implementations
> > and only a few "dynamic" ones - does it make sense to flip the logic
> > and introduce a new "use_dynamic_of_cells" flag instead?
>
> The problem is that there are more cases than just two. We can have:
> 1. No cells at all
> 2. Fixed cells in DT
> 3. Dynamic cells with references in DT
> 4. Driver specified cells (specified within config)
> 5. Cells defined in a global table
>
> So we need to reference DT cells explicitly (we can't just confirm /
> deny *dynamic* cells).
>
> Another solution would be to have "no_fixed_of_cells" but:
>
> 1. Personally I think negation is less clear / easy to follow
>
> 2. There may be actually more drivers with no fixed cells.
> I think I modified 18 drivers. It seems devm_nvmem_register() is
> referenced in 44 places. Few of them may be not actual users but it
> still seems to be about equal.
Thanks for this overview of all the special cases. Please add my:
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
for the following two drivers:
- drivers/nvmem/meson-efuse.c
- drivers/nvmem/meson-mx-efuse.c


Best regards,
Martin
diff mbox series

Patch

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");
 	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);
 
diff --git a/drivers/nvmem/imx-ocotp-scu.c b/drivers/nvmem/imx-ocotp-scu.c
index 399e1eb8b4c1..ec5cce7c6697 100644
--- a/drivers/nvmem/imx-ocotp-scu.c
+++ b/drivers/nvmem/imx-ocotp-scu.c
@@ -220,6 +220,7 @@  static int imx_scu_ocotp_write(void *context, unsigned int offset,
 
 static struct nvmem_config imx_scu_ocotp_nvmem_config = {
 	.name = "imx-scu-ocotp",
+	.use_fixed_of_cells = true,
 	.read_only = false,
 	.word_size = 4,
 	.stride = 1,
diff --git a/drivers/nvmem/imx-ocotp.c b/drivers/nvmem/imx-ocotp.c
index e9b52ecb3f72..e37a82f98ba6 100644
--- a/drivers/nvmem/imx-ocotp.c
+++ b/drivers/nvmem/imx-ocotp.c
@@ -616,6 +616,7 @@  static int imx_ocotp_probe(struct platform_device *pdev)
 		return PTR_ERR(priv->clk);
 
 	priv->params = of_device_get_match_data(&pdev->dev);
+	imx_ocotp_nvmem_config.use_fixed_of_cells = true;
 	imx_ocotp_nvmem_config.size = 4 * priv->params->nregs;
 	imx_ocotp_nvmem_config.dev = dev;
 	imx_ocotp_nvmem_config.priv = priv;
diff --git a/drivers/nvmem/meson-efuse.c b/drivers/nvmem/meson-efuse.c
index d6b533497ce1..657e171d5af3 100644
--- a/drivers/nvmem/meson-efuse.c
+++ b/drivers/nvmem/meson-efuse.c
@@ -93,6 +93,7 @@  static int meson_efuse_probe(struct platform_device *pdev)
 
 	econfig->dev = dev;
 	econfig->name = dev_name(dev);
+	econfig->use_fixed_of_cells = true;
 	econfig->stride = 1;
 	econfig->word_size = 1;
 	econfig->reg_read = meson_efuse_read;
diff --git a/drivers/nvmem/meson-mx-efuse.c b/drivers/nvmem/meson-mx-efuse.c
index 13eb14316f46..7cc51391ec9c 100644
--- a/drivers/nvmem/meson-mx-efuse.c
+++ b/drivers/nvmem/meson-mx-efuse.c
@@ -213,6 +213,7 @@  static int meson_mx_efuse_probe(struct platform_device *pdev)
 	efuse->config.owner = THIS_MODULE;
 	efuse->config.dev = &pdev->dev;
 	efuse->config.priv = efuse;
+	efuse->config.use_fixed_of_cells = true;
 	efuse->config.stride = drvdata->word_size;
 	efuse->config.word_size = drvdata->word_size;
 	efuse->config.size = SZ_512;
diff --git a/drivers/nvmem/microchip-otpc.c b/drivers/nvmem/microchip-otpc.c
index 436e0dc4f337..fb920fd7a8fc 100644
--- a/drivers/nvmem/microchip-otpc.c
+++ b/drivers/nvmem/microchip-otpc.c
@@ -261,6 +261,7 @@  static int mchp_otpc_probe(struct platform_device *pdev)
 		return ret;
 
 	mchp_nvmem_config.dev = otpc->dev;
+	mchp_nvmem_config.use_fixed_of_cells = true;
 	mchp_nvmem_config.size = size;
 	mchp_nvmem_config.priv = otpc;
 	nvmem = devm_nvmem_register(&pdev->dev, &mchp_nvmem_config);
diff --git a/drivers/nvmem/mtk-efuse.c b/drivers/nvmem/mtk-efuse.c
index a08e0aedd21c..1947337a121f 100644
--- a/drivers/nvmem/mtk-efuse.c
+++ b/drivers/nvmem/mtk-efuse.c
@@ -45,6 +45,7 @@  static int mtk_efuse_probe(struct platform_device *pdev)
 	if (IS_ERR(priv->base))
 		return PTR_ERR(priv->base);
 
+	econfig.use_fixed_of_cells = true;
 	econfig.stride = 1;
 	econfig.word_size = 1;
 	econfig.reg_read = mtk_reg_read;
diff --git a/drivers/nvmem/qcom-spmi-sdam.c b/drivers/nvmem/qcom-spmi-sdam.c
index f822790db49e..b547def94b5b 100644
--- a/drivers/nvmem/qcom-spmi-sdam.c
+++ b/drivers/nvmem/qcom-spmi-sdam.c
@@ -142,6 +142,7 @@  static int sdam_probe(struct platform_device *pdev)
 	sdam->sdam_config.name = "spmi_sdam";
 	sdam->sdam_config.id = NVMEM_DEVID_AUTO;
 	sdam->sdam_config.owner = THIS_MODULE;
+	sdam->sdam_config.use_fixed_of_cells = true;
 	sdam->sdam_config.stride = 1;
 	sdam->sdam_config.word_size = 1;
 	sdam->sdam_config.reg_read = sdam_read;
diff --git a/drivers/nvmem/qfprom.c b/drivers/nvmem/qfprom.c
index c1e893c8a247..eb126d507561 100644
--- a/drivers/nvmem/qfprom.c
+++ b/drivers/nvmem/qfprom.c
@@ -357,6 +357,7 @@  static int qfprom_probe(struct platform_device *pdev)
 {
 	struct nvmem_config econfig = {
 		.name = "qfprom",
+		.use_fixed_of_cells = true,
 		.stride = 1,
 		.word_size = 1,
 		.id = NVMEM_DEVID_AUTO,
diff --git a/drivers/nvmem/rave-sp-eeprom.c b/drivers/nvmem/rave-sp-eeprom.c
index c456011b75e8..e9b4c7927e37 100644
--- a/drivers/nvmem/rave-sp-eeprom.c
+++ b/drivers/nvmem/rave-sp-eeprom.c
@@ -328,6 +328,7 @@  static int rave_sp_eeprom_probe(struct platform_device *pdev)
 	of_property_read_string(np, "zii,eeprom-name", &config.name);
 	config.priv		= eeprom;
 	config.dev		= dev;
+	config.use_fixed_of_cells	= true;
 	config.size		= size;
 	config.reg_read		= rave_sp_eeprom_reg_read;
 	config.reg_write	= rave_sp_eeprom_reg_write;
diff --git a/drivers/nvmem/rockchip-efuse.c b/drivers/nvmem/rockchip-efuse.c
index e4579de5d014..211f6e7401a9 100644
--- a/drivers/nvmem/rockchip-efuse.c
+++ b/drivers/nvmem/rockchip-efuse.c
@@ -205,6 +205,7 @@  static int rockchip_rk3399_efuse_read(void *context, unsigned int offset,
 
 static struct nvmem_config econfig = {
 	.name = "rockchip-efuse",
+	.use_fixed_of_cells = true,
 	.stride = 1,
 	.word_size = 1,
 	.read_only = true,
diff --git a/drivers/nvmem/sc27xx-efuse.c b/drivers/nvmem/sc27xx-efuse.c
index c825fc902d10..ed5cc4f3e2bc 100644
--- a/drivers/nvmem/sc27xx-efuse.c
+++ b/drivers/nvmem/sc27xx-efuse.c
@@ -248,6 +248,7 @@  static int sc27xx_efuse_probe(struct platform_device *pdev)
 	econfig.reg_read = sc27xx_efuse_read;
 	econfig.priv = efuse;
 	econfig.dev = &pdev->dev;
+	econfig.use_fixed_of_cells = true;
 	nvmem = devm_nvmem_register(&pdev->dev, &econfig);
 	if (IS_ERR(nvmem)) {
 		dev_err(&pdev->dev, "failed to register nvmem config\n");
diff --git a/drivers/nvmem/sprd-efuse.c b/drivers/nvmem/sprd-efuse.c
index 4f1fcbfec394..ef3161645f60 100644
--- a/drivers/nvmem/sprd-efuse.c
+++ b/drivers/nvmem/sprd-efuse.c
@@ -408,6 +408,7 @@  static int sprd_efuse_probe(struct platform_device *pdev)
 	econfig.read_only = false;
 	econfig.name = "sprd-efuse";
 	econfig.size = efuse->data->blk_nums * SPRD_EFUSE_BLOCK_WIDTH;
+	econfig.use_fixed_of_cells = true;
 	econfig.reg_read = sprd_efuse_read;
 	econfig.reg_write = sprd_efuse_write;
 	econfig.priv = efuse;
diff --git a/drivers/nvmem/stm32-romem.c b/drivers/nvmem/stm32-romem.c
index ba779e26937a..3d3e557cb88f 100644
--- a/drivers/nvmem/stm32-romem.c
+++ b/drivers/nvmem/stm32-romem.c
@@ -208,6 +208,7 @@  static int stm32_romem_probe(struct platform_device *pdev)
 	priv->cfg.priv = priv;
 	priv->cfg.owner = THIS_MODULE;
 	priv->cfg.type = NVMEM_TYPE_OTP;
+	priv->cfe.use_fixed_of_cells = true;
 
 	priv->lower = 0;
 
diff --git a/drivers/nvmem/sunplus-ocotp.c b/drivers/nvmem/sunplus-ocotp.c
index 52b928a7a6d5..57e3e0833b85 100644
--- a/drivers/nvmem/sunplus-ocotp.c
+++ b/drivers/nvmem/sunplus-ocotp.c
@@ -145,6 +145,7 @@  static int sp_ocotp_read(void *priv, unsigned int offset, void *value, size_t by
 
 static struct nvmem_config sp_ocotp_nvmem_config = {
 	.name = "sp-ocotp",
+	.use_fixed_of_cells = true,
 	.read_only = true,
 	.word_size = 1,
 	.size = QAC628_OTP_SIZE,
diff --git a/drivers/nvmem/sunxi_sid.c b/drivers/nvmem/sunxi_sid.c
index a970f1741cc6..6ab7aa3724a0 100644
--- a/drivers/nvmem/sunxi_sid.c
+++ b/drivers/nvmem/sunxi_sid.c
@@ -156,6 +156,7 @@  static int sunxi_sid_probe(struct platform_device *pdev)
 	nvmem_cfg->dev = dev;
 	nvmem_cfg->name = "sunxi-sid";
 	nvmem_cfg->type = NVMEM_TYPE_OTP;
+	nvmem_cfg->use_fixed_of_cells = true;
 	nvmem_cfg->read_only = true;
 	nvmem_cfg->size = cfg->size;
 	nvmem_cfg->word_size = 1;
diff --git a/drivers/nvmem/uniphier-efuse.c b/drivers/nvmem/uniphier-efuse.c
index aca910b3b6f8..69b9dfe6ab6e 100644
--- a/drivers/nvmem/uniphier-efuse.c
+++ b/drivers/nvmem/uniphier-efuse.c
@@ -53,6 +53,7 @@  static int uniphier_efuse_probe(struct platform_device *pdev)
 	econfig.size = resource_size(res);
 	econfig.priv = priv;
 	econfig.dev = dev;
+	econfig.use_fixed_of_cells = true;
 	nvmem = devm_nvmem_register(dev, &econfig);
 
 	return PTR_ERR_OR_ZERO(nvmem);
diff --git a/drivers/nvmem/zynqmp_nvmem.c b/drivers/nvmem/zynqmp_nvmem.c
index e28d7b133e11..d13750a4c112 100644
--- a/drivers/nvmem/zynqmp_nvmem.c
+++ b/drivers/nvmem/zynqmp_nvmem.c
@@ -58,6 +58,7 @@  static int zynqmp_nvmem_probe(struct platform_device *pdev)
 
 	priv->dev = dev;
 	econfig.dev = dev;
+	econfig.use_fixed_of_cells = true;
 	econfig.reg_read = zynqmp_nvmem_read;
 	econfig.priv = priv;
 
diff --git a/drivers/rtc/nvmem.c b/drivers/rtc/nvmem.c
index 07ede21cee34..5cc039d92257 100644
--- a/drivers/rtc/nvmem.c
+++ b/drivers/rtc/nvmem.c
@@ -21,6 +21,7 @@  int devm_rtc_nvmem_register(struct rtc_device *rtc,
 
 	nvmem_config->dev = dev;
 	nvmem_config->owner = rtc->owner;
+	nvmem_config->use_fixed_of_cells = true;
 	nvmem = devm_nvmem_register(dev, nvmem_config);
 	if (IS_ERR(nvmem))
 		dev_err(dev, "failed to register nvmem device for RTC\n");
diff --git a/drivers/w1/slaves/w1_ds250x.c b/drivers/w1/slaves/w1_ds250x.c
index 7592c7050d1d..538722b41f87 100644
--- a/drivers/w1/slaves/w1_ds250x.c
+++ b/drivers/w1/slaves/w1_ds250x.c
@@ -168,6 +168,7 @@  static int w1_eprom_add_slave(struct w1_slave *sl)
 	struct nvmem_device *nvmem;
 	struct nvmem_config nvmem_cfg = {
 		.dev = &sl->dev,
+		.use_fixed_of_cells = true,
 		.reg_read = w1_nvmem_read,
 		.type = NVMEM_TYPE_OTP,
 		.read_only = true,
diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index 0262b86194eb..b3c14ce87a65 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -73,6 +73,7 @@  struct nvmem_cell_info {
  * @owner:	Pointer to exporter module. Used for refcounting.
  * @cells:	Optional array of pre-defined NVMEM cells.
  * @ncells:	Number of elements in cells.
+ * @use_fixed_of_cells:	Read fixed NVMEM cells from OF.
  * @keepout:	Optional array of keepout ranges (sorted ascending by start).
  * @nkeepout:	Number of elements in the keepout array.
  * @type:	Type of the nvmem storage
@@ -103,6 +104,7 @@  struct nvmem_config {
 	struct module		*owner;
 	const struct nvmem_cell_info	*cells;
 	int			ncells;
+	bool			use_fixed_of_cells;
 	const struct nvmem_keepout *keepout;
 	unsigned int		nkeepout;
 	enum nvmem_type		type;