ad7793: sysfs: cannot create duplicate filename sampling_frequency

Hi,

I'm running a Sitara based system which utilizes a AD7792 ADC via the ad7793 IIO driver.
I recently started to move our kernel from 4.9 to 4.14 and ran into the following error when initializing the driver:

[    3.064265] ------------[ cut here ]------------
[    3.064281] WARNING: CPU: 1 PID: 1 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x68/0x78
[    3.064285] sysfs: cannot create duplicate filename '/devices/platform/44000000.ocp/4809a000.spi/spi_master/spi2/spi2.0/iio:device0/sampling_frequency'
[    3.064287] Modules linked in:
[    3.064297] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.14.23-01865-g1e22765 #195
[    3.064301] Hardware name: Generic DRA74X (Flattened Device Tree)
[    3.064321] [<c0210084>] (unwind_backtrace) from [<c020b840>] (show_stack+0x10/0x14)
[    3.064334] [<c020b840>] (show_stack) from [<c09e3d50>] (dump_stack+0x7c/0x90)
[    3.064348] [<c09e3d50>] (dump_stack) from [<c0235e4c>] (__warn+0xec/0x104)
[    3.064358] [<c0235e4c>] (__warn) from [<c0235e9c>] (warn_slowpath_fmt+0x38/0x48)
[    3.064366] [<c0235e9c>] (warn_slowpath_fmt) from [<c03bbf8c>] (sysfs_warn_dup+0x68/0x78)
[    3.064376] [<c03bbf8c>] (sysfs_warn_dup) from [<c03bbca0>] (sysfs_add_file_mode_ns+0x148/0x194)
[    3.064384] [<c03bbca0>] (sysfs_add_file_mode_ns) from [<c03bc5ec>] (internal_create_group+0xf8/0x2e8)
[    3.064392] [<c03bc5ec>] (internal_create_group) from [<c03bcb70>] (sysfs_create_groups+0x44/0x80)
[    3.064402] [<c03bcb70>] (sysfs_create_groups) from [<c0601a74>] (device_add+0x2f4/0x588)
[    3.064414] [<c0601a74>] (device_add) from [<c0356c88>] (cdev_device_add+0x4c/0x80)
[    3.064427] [<c0356c88>] (cdev_device_add) from [<c07c1410>] (iio_device_register+0x4d4/0x6d8)
[    3.064438] [<c07c1410>] (iio_device_register) from [<c07c6e64>] (ad7793_probe+0x1f0/0x48c)
[    3.064449] [<c07c6e64>] (ad7793_probe) from [<c067481c>] (spi_drv_probe+0x7c/0xa8)
[    3.064460] [<c067481c>] (spi_drv_probe) from [<c06043b0>] (driver_probe_device+0x238/0x2e8)
[    3.064470] [<c06043b0>] (driver_probe_device) from [<c0604504>] (__driver_attach+0xa4/0xa8)
[    3.064478] [<c0604504>] (__driver_attach) from [<c060291c>] (bus_for_each_dev+0x4c/0x9c)
[    3.064487] [<c060291c>] (bus_for_each_dev) from [<c0603928>] (bus_add_driver+0x18c/0x210)
[    3.064496] [<c0603928>] (bus_add_driver) from [<c0604b60>] (driver_register+0x78/0xf4)
[    3.064504] [<c0604b60>] (driver_register) from [<c0201b3c>] (do_one_initcall+0x44/0x168)
[    3.064516] [<c0201b3c>] (do_one_initcall) from [<c1000de8>] (kernel_init_freeable+0x148/0x1d4)
[    3.064526] [<c1000de8>] (kernel_init_freeable) from [<c09f6e70>] (kernel_init+0x8/0x108)
[    3.064534] [<c09f6e70>] (kernel_init) from [<c0207a98>] (ret_from_fork+0x14/0x3c)
[    3.064543] ---[ end trace ad59e170138815c0 ]---
[    3.064815] ad7793: probe of spi2.0 failed with error -17

I did some digging and came to the conclusion that there is basically a conflict between the different ways to handle the 'sampling_frequency' declaration.

The driver utilizes this way

static IIO_DEV_ATTR_SAMP_FREQ(S_IWUSR | S_IRUGO,

		ad7793_read_frequency,
		ad7793_write_frequency);

to define the handling. But in the header "ad_sigma_delta.h"

.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ)

is used.

I was not able to find a documentation on this but I'm guessing that these both ways are mutual exclusive?

The problem seems to be introduced with commit a13e831f which changes the mentioned header (which is shared between multiple AD devices) in combination with the staging ad7192 driver.

From a quick look the other drivers using this header don't use the __AD_SD_CHANNEL macro so they don't run into this problem.

So a fix would be to either revert that commit or to update the ad7793 driver accordingly. If this would be of interest I would supply a patch.

Regards,
Michael