Re: [PATCH v1 06/14] nvmem: core: introduce NVMEM layouts

From: Michael Walle
Date: Tue Aug 30 2022 - 10:25:01 EST

Am 2022-08-30 15:36, schrieb Srinivas Kandagatla:
On 25/08/2022 22:44, Michael Walle wrote:
NVMEM layouts are used to generate NVMEM cells during runtime. Think of
an EEPROM with a well-defined conent. For now, the content can be
described by a device tree or a board file. But this only works if the
offsets and lengths are static and don't change. One could also argue
that putting the layout of the EEPROM in the device tree is the wrong
place. Instead, the device tree should just have a specific compatible
string.

Right now there are two use cases:
(1) The NVMEM cell needs special processing. E.g. if it only specifies
a base MAC address offset and you need to add an offset, or it
needs to parse a MAC from ASCII format or some proprietary format.
(Post processing of cells is added in a later commit).
(2) u-boot environment parsing. The cells don't have a particular
offset but it needs parsing the content to determine the offsets
and length.

Signed-off-by: Michael Walle <michael@xxxxxxxx>
---
drivers/nvmem/Kconfig | 2 ++
drivers/nvmem/Makefile | 1 +
drivers/nvmem/core.c | 57 ++++++++++++++++++++++++++++++++++
drivers/nvmem/layouts/Kconfig | 5 +++
drivers/nvmem/layouts/Makefile | 4 +++
include/linux/nvmem-provider.h | 38 +++++++++++++++++++++++
6 files changed, 107 insertions(+)
create mode 100644 drivers/nvmem/layouts/Kconfig
create mode 100644 drivers/nvmem/layouts/Makefile

update to ./Documentation/driver-api/nvmem.rst would help others.

Sure. Didn't know about that one.

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index bab8a29c9861..1416837b107b 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -357,4 +357,6 @@ config NVMEM_U_BOOT_ENV
If compiled as module it will be called nvmem_u-boot-env.
+source "drivers/nvmem/layouts/Kconfig"
+
endif
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 399f9972d45b..cd5a5baa2f3a 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -5,6 +5,7 @@
obj-$(CONFIG_NVMEM) += nvmem_core.o
nvmem_core-y := core.o
+obj-y += layouts/
# Devices
obj-$(CONFIG_NVMEM_BCM_OCOTP) += nvmem-bcm-ocotp.o
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 3dfd149374a8..5357fc378700 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -74,6 +74,9 @@ static LIST_HEAD(nvmem_lookup_list);
static BLOCKING_NOTIFIER_HEAD(nvmem_notifier);
+static DEFINE_SPINLOCK(nvmem_layout_lock);
+static LIST_HEAD(nvmem_layouts);
+
static int __nvmem_reg_read(struct nvmem_device *nvmem, unsigned int offset,
void *val, size_t bytes)
{
@@ -744,6 +747,56 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
return 0;
}
+int nvmem_register_layout(struct nvmem_layout *layout)
+{
+ spin_lock(&nvmem_layout_lock);
+ list_add(&layout->node, &nvmem_layouts);
+ spin_unlock(&nvmem_layout_lock);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(nvmem_register_layout);

we should provide nvmem_unregister_layout too, so that providers can
add them if they can in there respective drivers.

Actually, that was the idea; that you can have layouts outside of layouts/.
I also had a nvmem_unregister_layout() but removed it because it was dead
code. Will re-add it again.

+
+static struct nvmem_layout *nvmem_get_compatible_layout(struct device_node *np)
+{
+ struct nvmem_layout *p, *ret = NULL;
+
+ spin_lock(&nvmem_layout_lock);
+
+ list_for_each_entry(p, &nvmem_layouts, node) {
+ if (of_match_node(p->of_match_table, np)) {
+ ret = p;
+ break;
+ }
+ }
+
+ spin_unlock(&nvmem_layout_lock);
+
+ return ret;
+}
+
+static int nvmem_add_cells_from_layout(struct nvmem_device *nvmem)
+{
+ struct nvmem_layout *layout;
+
+ layout = nvmem_get_compatible_layout(nvmem->dev.of_node);
+ if (layout)
+ layout->add_cells(&nvmem->dev, nvmem, layout);

access to add_cells can crash hear as we did not check it before
adding in to list.
Or
we could relax add_cells callback for usecases like imx-octop.

good catch, will use layout && layout->add_cells.

+
+ return 0;
+}
+
+const void *nvmem_layout_get_match_data(struct nvmem_device *nvmem,
+ struct nvmem_layout *layout)
+{
+ const struct of_device_id *match;
+
+ match = of_match_node(layout->of_match_table, nvmem->dev.of_node);
+
+ return match ? match->data : NULL;
+}
+EXPORT_SYMBOL_GPL(nvmem_layout_get_match_data);
+
/**
* nvmem_register() - Register a nvmem device for given nvmem_config.
* Also creates a binary entry in /sys/bus/nvmem/devices/dev-name/nvmem
@@ -872,6 +925,10 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
if (rval)
goto err_remove_cells;
+ rval = nvmem_add_cells_from_layout(nvmem);
+ if (rval)
+ goto err_remove_cells;
+
blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
return nvmem;
diff --git a/drivers/nvmem/layouts/Kconfig b/drivers/nvmem/layouts/Kconfig
new file mode 100644
index 000000000000..9ad3911d1605
--- /dev/null
+++ b/drivers/nvmem/layouts/Kconfig
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menu "Layout Types"
+
+endmenu
diff --git a/drivers/nvmem/layouts/Makefile b/drivers/nvmem/layouts/Makefile
new file mode 100644
index 000000000000..6fdb3c60a4fa
--- /dev/null
+++ b/drivers/nvmem/layouts/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for nvmem layouts.
+#
diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index e710404959e7..323685841e9f 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -127,6 +127,28 @@ struct nvmem_cell_table {
struct list_head node;
};
+/**
+ * struct nvmem_layout - NVMEM layout definitions
+ *
+ * @name: Layout name.
+ * @of_match_table: Open firmware match table.
+ * @add_cells: Will be called if a nvmem device is found which
+ * has this layout. The function will add layout
+ * specific cells with nvmem_add_one_cell().
+ * @node: List node.
+ *
+ * A nvmem device can hold a well defined structure which can just be
+ * evaluated during runtime. For example a TLV list, or a list of "name=val"
+ * pairs. A nvmem layout can parse the nvmem device and add appropriate
+ * cells.
+ */
+struct nvmem_layout {
+ const char *name;
+ const struct of_device_id *of_match_table;

looking at this, I think its doable to convert the existing
cell_post_process callback to layouts by adding a layout specific
callback here.

can you elaborate on that?

-michael