[PATCH 1/2] mtd: spi-nor: drop fw_devlink suppliers below a flash that failed to probe

[Manikandan Muralidharan <manikandan.m@microchip.com>]

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.

Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
---
 drivers/mtd/spi-nor/core.c | 26 +++++++++++++++++++++++++-
 drivers/nvmem/core.c       | 13 ++++++++++++-
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index a034dce7c839..57faab89f5af 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -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);
 
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 2e07f95de7ff..be3a05150085 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -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