nvmem: include bit index in cell sysfs file name

Creating sysfs files for all Cells caused a boot failure for linux-6.8-rc1 on
Apple M1, which (in downstream dts files) has multiple nvmem cells that use the
same byte address. This causes the device probe to fail with

[    0.605336] sysfs: cannot create duplicate filename '/devices/platform/soc@200000000/2922bc000.efuse/apple_efuses_nvmem0/cells/efuse@a10'
[    0.605347] CPU: 7 PID: 1 Comm: swapper/0 Tainted: G S                 6.8.0-rc1-arnd-5+ #133
[    0.605355] Hardware name: Apple Mac Studio (M1 Ultra, 2022) (DT)
[    0.605362] Call trace:
[    0.605365]  show_stack+0x18/0x2c
[    0.605374]  dump_stack_lvl+0x60/0x80
[    0.605383]  dump_stack+0x18/0x24
[    0.605388]  sysfs_warn_dup+0x64/0x80
[    0.605395]  sysfs_add_bin_file_mode_ns+0xb0/0xd4
[    0.605402]  internal_create_group+0x268/0x404
[    0.605409]  sysfs_create_groups+0x38/0x94
[    0.605415]  devm_device_add_groups+0x50/0x94
[    0.605572]  nvmem_populate_sysfs_cells+0x180/0x1b0
[    0.605682]  nvmem_register+0x38c/0x470
[    0.605789]  devm_nvmem_register+0x1c/0x6c
[    0.605895]  apple_efuses_probe+0xe4/0x120
[    0.606000]  platform_probe+0xa8/0xd0

As far as I can tell, this is a problem for any device with multiple cells on
different bits of the same address. Avoid the issue by changing the file name
to include the first bit number.

Fixes: 0331c611 ("nvmem: core: Expose cells through sysfs")
Link: https://github.com/AsahiLinux/linux/blob/bd0a1a7d4/arch/arm64/boot/dts/apple/t600x-dieX.dtsi#L156
Cc:  <regressions@lists.linux.dev>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Rafał Miłecki <rafal@milecki.pl>
Cc: Chen-Yu Tsai <wenst@chromium.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:  <asahi@lists.linux.dev>
Cc: Sven Peter <sven@svenpeter.dev>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20240209163454.98051-1-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-nvmem-cells

@@ -4,18 +4,18 @@ KernelVersion:	6.5
 Contact:	Miquel Raynal <miquel.raynal@bootlin.com>
 Description:
 		The "cells" folder contains one file per cell exposed by the
-		NVMEM device. The name of the file is: <name>@<where>, with
-		<name> being the cell name and <where> its location in the NVMEM
-		device, in hexadecimal (without the '0x' prefix, to mimic device
-		tree node names). The length of the file is the size of the cell
-		(when known). The content of the file is the binary content of
-		the cell (may sometimes be ASCII, likely without trailing
-		character).
+		NVMEM device. The name of the file is: "<name>@<byte>,<bit>",
+		with <name> being the cell name and <where> its location in
+		the NVMEM device, in hexadecimal bytes and bits (without the
+		'0x' prefix, to mimic device tree node names). The length of
+		the file is the size of the cell (when known). The content of
+		the file is the binary content of the cell (may sometimes be
+		ASCII, likely without trailing character).
 		Note: This file is only present if CONFIG_NVMEM_SYSFS
 		is enabled.
 
 		Example::
 
-		  hexdump -C /sys/bus/nvmem/devices/1-00563/cells/product-name@d
+		  hexdump -C /sys/bus/nvmem/devices/1-00563/cells/product-name@d,0
 		  00000000  54 4e 34 38 4d 2d 50 2d  44 4e         |TN48M-P-DN|
 		  0000000a

drivers/nvmem/core.c

@@ -460,8 +460,9 @@ static int nvmem_populate_sysfs_cells(struct nvmem_device *nvmem)
 	list_for_each_entry(entry, &nvmem->cells, node) {
 		sysfs_bin_attr_init(&attrs[i]);
 		attrs[i].attr.name = devm_kasprintf(&nvmem->dev, GFP_KERNEL,
-						    "%s@%x", entry->name,
-						    entry->offset);
+						    "%s@%x,%x", entry->name,
+						    entry->offset,
+						    entry->bit_offset);
 		attrs[i].attr.mode = 0444;
 		attrs[i].size = entry->bytes;
 		attrs[i].read = &nvmem_cell_attr_read;