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From:   Christophe Kerello <christophe.kerello@foss.st.com>
To:     <miquel.raynal@bootlin.com>, <richard@nod.at>, <vigneshr@ti.com>,
        <robh+dt@kernel.org>, <srinivas.kandagatla@linaro.org>
CC:     <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        <devicetree@vger.kernel.org>, <chenshumin86@sina.com>,
        Christophe Kerello <christophe.kerello@foss.st.com>
Subject: [PATCH v2 3/4] nvmem: core: Fix a conflict between MTD and NVMEM on wp-gpios property
Date:   Mon, 31 Jan 2022 10:57:54 +0100
Message-ID: <20220131095755.8981-4-christophe.kerello@foss.st.com>
In-Reply-To: <20220131095755.8981-1-christophe.kerello@foss.st.com>
References: <20220131095755.8981-1-christophe.kerello@foss.st.com>
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Wp-gpios property can be used on NVMEM nodes and the same property can
be also used on MTD NAND nodes. In case of the wp-gpios property is
defined at NAND level node, the GPIO management is done at NAND driver
level. Write protect is disabled when the driver is probed or resumed
and is enabled when the driver is released or suspended.

When no partitions are defined in the NAND DT node, then the NAND DT node
will be passed to NVMEM framework. If wp-gpios property is defined in
this node, the GPIO resource is taken twice and the NAND controller
driver fails to probe.

It would be possible to set config->wp_gpio at MTD level before calling
nvmem_register function but NVMEM framework will toggle this GPIO on
each write when this GPIO should only be controlled at NAND level driver
to ensure that the Write Protect has not been enabled.

A way to fix this conflict is to add a new boolean flag in nvmem_config
named skip_wp_gpio. In case skip_wp_gpio is set, the GPIO resource will
be managed by the provider.

Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
---
Changes in v2:
 - rework the proposal done to fix a conflict between MTD and NVMEM on
   wp-gpios property.

 drivers/nvmem/core.c           | 2 +-
 include/linux/nvmem-provider.h | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 23a38dcf0fc4..cb40dca6a51d 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -771,7 +771,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 
 	if (config->wp_gpio)
 		nvmem->wp_gpio = config->wp_gpio;
-	else
+	else if (!config->skip_wp_gpio)
 		nvmem->wp_gpio = gpiod_get_optional(config->dev, "wp",
 						    GPIOD_OUT_HIGH);
 	if (IS_ERR(nvmem->wp_gpio)) {
diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index 98efb7b5660d..4b480023c265 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -70,7 +70,8 @@ struct nvmem_keepout {
  * @word_size:	Minimum read/write access granularity.
  * @stride:	Minimum read/write access stride.
  * @priv:	User context passed to read/write callbacks.
- * @wp-gpio:   Write protect pin
+ * @wp-gpio:	Write protect pin
+ * @skip_wp_gpio: Write Protect pin is managed by the provider.
  *
  * Note: A default "nvmem<id>" name will be assigned to the device if
  * no name is specified in its configuration. In such case "<id>" is
@@ -92,6 +93,7 @@ struct nvmem_config {
 	enum nvmem_type		type;
 	bool			read_only;
 	bool			root_only;
+	bool			skip_wp_gpio;
 	struct device_node	*of_node;
 	bool			no_of_node;
 	nvmem_reg_read_t	reg_read;
-- 
2.25.1