linux-kernel - Re: [PATCH v1 5/5] pinctrl: microchip-sgpio: wait until output is actually set

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Date:   Sat, 26 Feb 2022 21:54:22 +0100
From:   Michael Walle <michael@...le.cc>
To:     Colin Foster <colin.foster@...advantage.com>
Cc:     Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        UNGLinuxDriver@...rochip.com, linux-arm-kernel@...ts.infradead.org,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 5/5] pinctrl: microchip-sgpio: wait until output is
 actually set

Hi Colin,

Am 2022-02-25 17:54, schrieb Colin Foster:
> On Fri, Feb 25, 2022 at 12:29:50PM +0100, Michael Walle wrote:
>> 
>> Could you also have a look at the other supported sgpio block,
>> the ocelot and the luton? I don't have any register description
>> of these.
> 
> The current supported Ocelot chips are the VSC7514 (link below) and the
> VSC7513. Chapter 6 of this PDF links a second PDF, and you should be
> able to find the Serial GPIO definitions in DEVCPU_GCB:SIO_CTRL on page
> 79 of that PDF.
> https://ww1.microchip.com/downloads/en/DeviceDoc/VMDS-10491.pdf

Thanks! I've just send a new version with support for these.

> I'm working on support for the VSC7511/7512, so I can run a "does it
> work" test, but I likely won't have a setup to test the corner
> conditions this patch set is addressing with any confidence.

You can time the register polling using ktime_get(), ktime_sub()
and ktime_to_ns(). It should be in the magnitude of the burst gap.
Which will give you at least some confidence. I did the testing
with an oscilloscope and toggling gpios (but also did measure
the timing with ktime_get()).

-michael