linux-kernel - Re: [PATCH v2] pinctrl: pinctrl-single: Fix pcs_parse_bits_in_pinctrl_entry to use _

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Date:	Sat, 23 Apr 2016 11:45:34 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Keerthy <j-keerthy@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tero Kristo <t-kristo@...com>, Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH v2] pinctrl: pinctrl-single: Fix pcs_parse_bits_in_pinctrl_entry
 to use __ffs than ffs

On Fri, Apr 15, 2016 at 5:22 PM, Tony Lindgren <tony@...mide.com> wrote:
> * Linus Walleij <linus.walleij@...aro.org> [160415 02:29]:
>> On Thu, Apr 14, 2016 at 6:59 AM, Keerthy <j-keerthy@...com> wrote:
>>
>> > 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@...com>
>> > ---
>> >
>> > Changes in v2:
>> >
>> >   * Changed pcs->fshift to use __ffs instead of ffs to be consistent.
>> >
>> > Boot tesed on da850-evm and checked the pinctrl sysfs nodes.
>>
>> Patch applied for fixes with Tony's ACK.
>>
>> Should it also be tagged for stable?
>
> Probably a good idea, I can see somebody pulling hair out because
> of this in various product trees.

Ooops sorry I totally missed to add that :(

Please ask Greg to take it as a selected stable patch.

Yours,
Linus Walleij