Re: [PATCH v2] pinctrl: pinctrl-single: Fix pcs_parse_bits_in_pinctrl_entry to use __ffs than ffs

[Tony Lindgren <tony@xxxxxxxxxxx>]

* Keerthy <j-keerthy@xxxxxx> [160413 22:00]:
> pcs_parse_bits_in_pinctrl_entry uses ffs which gives bit indices
> ranging from 1 to MAX. This leads to a corner case where we try to request
> the pin number = MAX and fails.
> 
> bit_pos value is being calculted using ffs. pin_num_from_lsb uses
> bit_pos value. pins array is populated with:
> 
> pin + pin_num_from_lsb.
> 
> The above is 1 more than usual bit indices as bit_pos uses ffs to compute
> first set bit. Hence the last of the pins array is populated with the MAX
> value and not MAX - 1 which causes error when we call pin_request.
>
> mask_pos is rightly calculated as ((pcs->fmask) << (bit_pos - 1))
> Consequently val_pos and submask are correct.
> 
> Hence use __ffs which gives (ffs(x) - 1) as the first bit set.
> 
> fixes: 4e7e8017a8 ("pinctrl: pinctrl-single: enhance to configure multiple pins of different modules")
> Signed-off-by: Keerthy <j-keerthy@xxxxxx>
> ---
> 
> Changes in v2:
> 
>   * Changed pcs->fshift to use __ffs instead of ffs to be consistent.

Thanks for updating it, looks good to me and still works here:

Acked-by: Tony Lindgren <tony@xxxxxxxxxxx>


> Boot tesed on da850-evm and checked the pinctrl sysfs nodes.
> 
>  drivers/pinctrl/pinctrl-single.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pinctrl/pinctrl-single.c b/drivers/pinctrl/pinctrl-single.c
> index fb126d5..cf9bafa 100644
> --- a/drivers/pinctrl/pinctrl-single.c
> +++ b/drivers/pinctrl/pinctrl-single.c
> @@ -1280,9 +1280,9 @@ static int pcs_parse_bits_in_pinctrl_entry(struct pcs_device *pcs,
>  
>  		/* Parse pins in each row from LSB */
>  		while (mask) {
> -			bit_pos = ffs(mask);
> +			bit_pos = __ffs(mask);
>  			pin_num_from_lsb = bit_pos / pcs->bits_per_pin;
> -			mask_pos = ((pcs->fmask) << (bit_pos - 1));
> +			mask_pos = ((pcs->fmask) << bit_pos);
>  			val_pos = val & mask_pos;
>  			submask = mask & mask_pos;
>  
> @@ -1852,7 +1852,7 @@ static int pcs_probe(struct platform_device *pdev)
>  	ret = of_property_read_u32(np, "pinctrl-single,function-mask",
>  				   &pcs->fmask);
>  	if (!ret) {
> -		pcs->fshift = ffs(pcs->fmask) - 1;
> +		pcs->fshift = __ffs(pcs->fmask);
>  		pcs->fmax = pcs->fmask >> pcs->fshift;
>  	} else {
>  		/* If mask property doesn't exist, function mux is invalid. */
> -- 
> 1.9.1
> 
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