linux-kernel - Re: [PATCH 1/2] gpio: gpio-74x164: add support for CDx4HC4094

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Message-ID: <CACRpkdbTypeq0M8VNb491GaZdBLyE9_TFpCDn5omnTe8D+BU7w@mail.gmail.com>
Date:   Tue, 26 Jul 2022 09:23:08 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Marcus Folkesson <marcus.folkesson@...il.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maxime Ripard <mripard@...nel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] gpio: gpio-74x164: add support for CDx4HC4094

On Tue, Jul 26, 2022 at 8:55 AM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Tue, Jul 26, 2022 at 12:22 AM Linus Walleij <linus.walleij@...aro.org> wrote:

> > Well it will work, because all values come out, however *during*
> > the transfer, not *after* the transfer as intended with the
> > STR signal.
>
> No. I think you missed one little but crucial detail. The strobe is
> edge, not level, while you consider CS as a level signal (only).

Aha! Then it works :)

> See Figure 7 and Table 9 in the datasheet you linked to. When STR is
> low, the data is not changed. Maybe it's not clear in this datasheet,
> I found somewhere
> in a more clear table.
>
> > At least how I see it ...?
>
> If what you are saying is true, the hardware is totally broken and I
> wouldn't use it. I.o.w. if the strobe passes all data when it's at low
> level and latches at low-to-high, it's broken by definition in my
> point of view.

I have seen strobes that are level-active in my life, but if you
say this one isn't then all is fine!

Yours,
Linus Walleij