Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220721093422.2173982-1-marcus.folkesson@gmail.com>
 <CAHp75VddBhc9peHXfNfTyTNni246kC8CyLqCrMFadn67LGDarQ@mail.gmail.com>
 <CACRpkdaczrU1tM5Yt7P-Q2h+ge8STOi6HvvYeTM-g+JwS8_gZw@mail.gmail.com>
 <CAHp75VfaExrFYto7LWa5Vnbm6JbiAqtutKmk0HzfeHmmi3PwOg@mail.gmail.com>
 <CACRpkdYHgD-fmt_2PWJrmyGY=AOP0Z+4jTkH=n3wJ+a0aApqcg@mail.gmail.com> <CAHp75Vf_aDSocdB7R6zKFwEOBRwq0w2m6GdCM-5ujKoz4bGiqQ@mail.gmail.com>
In-Reply-To: <CAHp75Vf_aDSocdB7R6zKFwEOBRwq0w2m6GdCM-5ujKoz4bGiqQ@mail.gmail.com>
From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Tue, 26 Jul 2022 09:23:08 +0200
Message-ID: <CACRpkdbTypeq0M8VNb491GaZdBLyE9_TFpCDn5omnTe8D+BU7w@mail.gmail.com>
Subject: Re: [PATCH 1/2] gpio: gpio-74x164: add support for CDx4HC4094
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Marcus Folkesson <marcus.folkesson@gmail.com>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Maxime Ripard <mripard@kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        devicetree <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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