linux-kernel - Re: [PATCH] pps-gpio: use IRQ edge config when not capturing both edges

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJ+vNU2NAjquPKKxx3xJtZqWiE=CZi5qCSEDu6dua1M0g9Ldjg@mail.gmail.com>
Date:   Tue, 12 Sep 2017 08:54:40 -0700
From:   Tim Harvey <tharvey@...eworks.com>
To:     Rodolfo Giometti <giometti@...eenne.com>
Cc:     "discussions@...uxpps.org" <discussions@...uxpps.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Koen Vandeputte <koen.vandeputte@...ntric.com>
Subject: Re: [PATCH] pps-gpio: use IRQ edge config when not capturing both edges

On Sun, Sep 10, 2017 at 3:43 AM, Rodolfo Giometti <giometti@...eenne.com> wrote:
> On 08/09/2017 21:53, Tim Harvey wrote:
>>
>> PPS signals with very short pulse-widths can be missed if their state
>> changes by the time the interrupt handler reads the GPIO pin state.
>>
>> To avoid this in the case where we are only looking for one edge we can
>> use the edge configuration for the pin state but fall back to reading the
>> pin if both edges are being watched.
>
>
> I disagree. The "rising_edge" status should be get from the hardware and not
> derived by an empirical computation. Or, at least, it should be specifically
> activated by setting something like this:
>
>         pps {
>                 pinctrl-names = "default";
>                 pinctrl-0 = <&pinctrl_pps>;
>
>                 gpios = <&gpio1 26 GPIO_ACTIVE_HIGH>;
>                 Yes-I-want-get-signal-status-in-an-epirical-way;
>
>                 compatible = "pps-gpio";
>                 status = "okay";
>         };
>
> This setting should also print a warning in order to be clear for the user
> that he/she should know what he/she is doing.
>
> Then the code should check also the compatibility with property
> "assert-falling-edge"...
>

Hi Rodolfo,

Do you agree with using the irq edge in general if/when it is
available to resolve the case where small pulse-widths can be caught?

I assumed because pps-gpio is the one configuring the irq based on
info->capture_clear and info->assert_falling_edge that that it made
sense to use that logic again when handling the interrupt but there is
likely a call I can make to determine the irq (edge) type based on the
irq.

Tim