mtd/nvmem: don't defer forever on absent NVMEM suppliers

A consumer that gets its MAC address from an NVMEM cell can be deferred forever when the cell will never appear, instead of falling back to another address source. These came up while testing the SFDP EUI-48 series [1], where macb reads its MAC address from a cell exposed by the QSPI flash, but both are generic:

- 1/2: when the SPI NOR flash is not populated or not reachable, nothing below its node is ever registered, yet fw_devlink keeps waiting on it and the NVMEM lookup keeps returning -EPROBE_DEFER. Drop the fw_devlink links below a flash that failed to probe, and return -ENOENT for a cell on a node fw_devlink has marked as never becoming a device.

- 2/2: a layout adds its cells from its probe and may add none, e.g. when the data the cell describes is not programmed on the device. Only defer while the layout is not bound yet, and return -ENOENT once it is.

In both cases the consumer then falls back, e.g. macb uses the address left by the bootloader or a random one.

This series depends on the SFDP EUI-48 series [1] and applies on top of it.

[1] https://lore.kernel.org/all/[email protected]/

Manikandan Muralidharan (2):
mtd: spi-nor: drop fw_devlink suppliers below a flash that failed to
probe
nvmem: core: don't defer for a missing cell once the layout is bound

 drivers/mtd/spi-nor/core.c | 26 ++++++++++++++++++++++++-
 drivers/nvmem/core.c       | 40 ++++++++++++++++++++++++++++++++++++--
 2 files changed, 63 insertions(+), 3 deletions(-)

base-commit: 05441d697f7f9a927264f4058cbbc6a03dfcac9d
prerequisite-patch-id: 76d8b1168f88c3e7912ac2ce01a705f7e69d8a3b
prerequisite-patch-id: b360d0d00ac1a6feb76d4b3f9412b6f1741f6161
prerequisite-patch-id: 659801d6f415ba79ce51f21b3a4f5e132348c150
prerequisite-patch-id: bd1a5a10983aa3cfd99c93ee58fdeb04cdd87b76
prerequisite-patch-id: 94ede38b6c2480cb1e0e102e9bbeb6ffd5b276ef
prerequisite-patch-id: ae3977b6c56c5bd4f352d77bd8a7883a69d390af
prerequisite-patch-id: 58d0ad25e81f16f60864d624eed7ff481607e960
prerequisite-patch-id: ba140b71fdbfc992861ae4c34b6acc737d4e4528

2.43.0

When a SPI NOR flash is not populated or not reachable, spi_nor_scan() fails and nothing described below the flash node (the SFDP NVMEM device, its nvmem-layout, partitions) is ever registered. fw_devlink still holds links from consumers of those nodes, so a consumer such as an Ethernet MAC whose "nvmem-cells" points at the SFDP EUI-48 cell waits for its supplier forever and is never probed:

platform f8008000.ethernet: deferred probe pending: platform: wait for supplier /ahb/apb/spi@f0024000/flash@0/sfdp/nvmem-layout/mac-address

On a permanent spi_nor_scan() failure, call fw_devlink_purge_absent_suppliers() on each child of the flash node. It marks the nodes that never became devices with FWNODE_FLAG_NOT_DEVICE and drops their consumer links, so the consumer is probed.

The consumer then probes, but of_nvmem_cell_get() still returns -EPROBE_DEFER because nvmem_device_match() does not find a device for the SFDP node. When fw_devlink has marked that node FWNODE_FLAG_NOT_DEVICE, it will never become a device, so return -ENOENT instead. The consumer can then fall back, e.g. macb uses a random MAC address.

---
 drivers/mtd/spi-nor/core.c | 26 +++++++++++++++++++++++++-
 drivers/nvmem/core.c       | 13 ++++++++++++-
 2 files changed, 37 insertions(+), 2 deletions(-)

index a034dce7c839..57faab89f5af 100644
@@ -12,6 +12,7 @@
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/errno.h>
+#include <linux/fwnode.h>
 #include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/mtd/mtd.h>

@@ -3624,6 +3625,25 @@ static int spi_nor_create_write_dirmap(struct spi_nor *nor)
 	return PTR_ERR_OR_ZERO(nor->dirmap.wdesc);
 }
 
+/**
+ * spi_nor_purge_absent_suppliers() - drop fw_devlink links below a missing
+ * flash
+ * @dev:	pointer to the flash 'struct device'
+ *
+ * When the flash cannot be probed (e.g. it is not populated or not
+ * reachable), nothing described below its node, such as the SFDP NVMEM
+ * device or the partitions, is ever registered. Mark those nodes as never
+ * becoming devices and drop their consumer links, so that consumers such as
+ * an Ethernet MAC using an NVMEM cell are not deferred forever.
+ */
+static void spi_nor_purge_absent_suppliers(struct device *dev)
+{
+	struct fwnode_handle *child;
+
+	device_for_each_child_node(dev, child)
+		fw_devlink_purge_absent_suppliers(child);
+}
+
 static int spi_nor_probe(struct spi_mem *spimem)
 {
 	struct spi_device *spi = spimem->spi;

@@ -3672,8 +3692,12 @@ static int spi_nor_probe(struct spi_mem *spimem)
 		flash_name = spi->modalias;
 
 	ret = spi_nor_scan(nor, flash_name, &hwcaps);
-	if (ret)
+	if (ret) {
+		/* A deferred probe (e.g. on the reset GPIO) may still succeed. */
+		if (ret != -EPROBE_DEFER)
+			spi_nor_purge_absent_suppliers(dev);
 		return ret;
+	}
 
 	spi_nor_debugfs_register(nor);
 

index 2e07f95de7ff..be3a05150085 100644
@@ -10,6 +10,7 @@
 #include <linux/device.h>
 #include <linux/export.h>
 #include <linux/fs.h>
+#include <linux/fwnode.h>
 #include <linux/idr.h>
 #include <linux/init.h>
 #include <linux/kref.h>

@@ -1458,11 +1459,21 @@ struct nvmem_cell *of_nvmem_cell_get(struct device_node *np, const char *id)
 	}
 
 	nvmem = nvmem_device_match(nvmem_np, device_match_of_node);
-	of_node_put(nvmem_np);
 	if (IS_ERR(nvmem)) {
+		/*
+		 * fw_devlink marks a node that will never become a device,
+		 * either because its parent failed to probe or because the
+		 * parent bound without registering it. Don't defer for it.
+		 */
+		if (PTR_ERR(nvmem) == -EPROBE_DEFER &&
+		    fwnode_test_flag(of_fwnode_handle(nvmem_np),
+				     FWNODE_FLAG_NOT_DEVICE))
+			nvmem = ERR_PTR(-ENOENT);
+		of_node_put(nvmem_np);
 		of_node_put(cell_np);
 		return ERR_CAST(nvmem);
 	}
+	of_node_put(nvmem_np);
 
 	ret = nvmem_layout_module_get_optional(nvmem);
 	if (ret) {

2.43.0

of_nvmem_cell_get() returns -EPROBE_DEFER whenever a requested cell is not found and the nvmem device has a layout, assuming the layout has not added its cells yet. A layout may add none, e.g. when the data the cell describes is not programmed on the device. The layout is then bound but the cell is never going to show up, and the consumer is deferred forever instead of falling back.

Only defer while the layout device is not bound yet, and return -ENOENT once it is, so that a consumer such as an Ethernet MAC can fall back to a random address.

---
 drivers/nvmem/core.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

index be3a05150085..f34a35a04e55 100644
@@ -1403,6 +1403,31 @@ static int nvmem_layout_module_get_optional(struct nvmem_device *nvmem)
 	return 0;
 }
 
+/**
+ * nvmem_layout_pending() - Check whether a layout may still add cells
+ * @nvmem: nvmem device the layout belongs to
+ *
+ * A layout adds its cells from its probe. Once the layout device is bound,
+ * a cell that is still missing is never going to show up.
+ *
+ * Return: true if @nvmem has a layout that is not bound yet, false otherwise.
+ */
+static bool nvmem_layout_pending(struct nvmem_device *nvmem)
+{
+	struct device *dev;
+	bool bound;
+
+	if (!nvmem->layout)
+		return false;
+
+	dev = &nvmem->layout->dev;
+	device_lock(dev);
+	bound = device_is_bound(dev);
+	device_unlock(dev);
+
+	return !bound;
+}
+
 /**
  * of_nvmem_cell_get() - Get a nvmem cell from given device node and cell id
  *

@@ -1486,7 +1511,7 @@ struct nvmem_cell *of_nvmem_cell_get(struct device_node *np, const char *id)
 	of_node_put(cell_np);
 	if (!cell_entry) {
 		nvmem_layout_module_put(nvmem);
-		ret = nvmem->layout ? -EPROBE_DEFER : -ENOENT;
+		ret = nvmem_layout_pending(nvmem) ? -EPROBE_DEFER : -ENOENT;
 		nvmem_device_put(nvmem);
 		return ERR_PTR(ret);
 	}

2.43.0