Re: [PATCH v2] iio: Fix scan mask subset check logic

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Tue, 29 Apr 2025 17:17:17 -0300
Fabio Estevam <festevam@gmail.com> wrote:

> From: Fabio Estevam <festevam@denx.de>
> 
> Since commit 2718f15403fb ("iio: sanity check available_scan_masks array"),
> verbose and misleading warnings are printed for devices like the MAX11601:
> 
> max1363 1-0064: available_scan_mask 8 subset of 0. Never used
> max1363 1-0064: available_scan_mask 9 subset of 0. Never used
> max1363 1-0064: available_scan_mask 10 subset of 0. Never used
> max1363 1-0064: available_scan_mask 11 subset of 0. Never used
> max1363 1-0064: available_scan_mask 12 subset of 0. Never used
> max1363 1-0064: available_scan_mask 13 subset of 0. Never used
> ...
> [warnings continue] 
> 
> Adding some debug prints show that the mask1 and mask2 indexes
> are incorrectly computed, leading to wrong array access.

Just for reference, as per the max1363 thread, the
bug isn't what is changed here, but rather another driver side problem.

> 
> These incorrect accesses causes the wrong subset output:
> 
> iio-core: ******** mask1[0] is 0x1
> iio-core: ******** mask2[1] is 0x4
> iio-core: ******** mask2[2] is 0x3
> iio-core: ******** mask2[3] is 0xf
> iio-core: ******** mask2[4] is 0x1000
> iio-core: ******** mask2[5] is 0x40000
> iio-core: ******** mask2[6] is 0x3000
> iio-core: ******** mask2[7] is 0x0
> iio-core: ******** mask2[8] is 0xffff0000000e2720
> max1363 1-0064: available_scan_mask 8 subset of 0. Never used
> iio-core: ******** mask2[9] is 0xffff0000000e2660
> max1363 1-0064: available_scan_mask 9 subset of 0. Never used
> iio-core: ******** mask2[10] is 0xffff0000000e25a0
> max1363 1-0064: available_scan_mask 10 subset of 0. Never used
> iio-core: ******** mask2[11] is 0xffff0000000e24e0
> max1363 1-0064: available_scan_mask 11 subset of 0. Never used
> iio-core: ******** mask2[12] is 0xffff0000000e2420
> max1363 1-0064: available_scan_mask 12 subset of 0. Never used
> iio-core: ******** mask2[13] is 0xffff0000000e2360
> max1363 1-0064: available_scan_mask 13 subset of 0. Never used
> 
> Fix the available_scan_masks sanity check logic so that it
> only prints the warning when an element of available_scan_mask
> is in fact a subset of a previous one.
> 
> With this fix, the warning output becomes both correct and more
> informative:
> 
> max1363 1-0064: Mask 7 (0xc) is a subset of mask 6 (0xf) and will be ignored.
> 
> Cc: stable@vger.kernel.org
> Fixes: 2718f15403fb ("iio: sanity check available_scan_masks array")
> Signed-off-by: Fabio Estevam <festevam@denx.de>
> ---
> Changes since v1:
> - Make it a standalone patch. max1363 fix will be sent later.
> - Keep using bitmap_subset().
> - Add more information about the error in the commit log.
> 
>  drivers/iio/industrialio-core.c | 18 +++++-------------
>  1 file changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 6a6568d4a2cb..dabfcb50e5fe 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -1947,21 +1947,13 @@ static void iio_sanity_check_avail_scan_masks(struct iio_dev *indio_dev)
>  	 * available masks in the order of preference (presumably the least
>  	 * costy to access masks first).
>  	 */
> -	for (i = 0; i < num_masks - 1; i++) {
> -		const unsigned long *mask1;
> -		int j;
>  
> -		mask1 = av_masks + i * longs_per_mask;
> -		for (j = i + 1; j < num_masks; j++) {
> -			const unsigned long *mask2;
> -
> -			mask2 = av_masks + j * longs_per_mask;
> -			if (bitmap_subset(mask2, mask1, masklength))
> +	for (i = 1; i < num_masks; i++)
> +		for (int j = 0; j < i; j++)
> +			if (bitmap_subset(&av_masks[i], &av_masks[j], BITS_PER_LONG))
>  				dev_warn(indio_dev->dev.parent,
> -					 "available_scan_mask %d subset of %d. Never used\n",
> -					 j, i);
> -		}
> -	}
> +					 "Mask %d (0x%lx) is a subset of mask %d (0x%lx) and will be ignored.\n",
> +					 i, av_masks[i], j, av_masks[j]);
>  }
>  
>  /**