linux-kernel - Re: [PATCHv3] w1: omap-hdq: Simplify driver with PM runtime autosuspend

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Date:   Tue, 21 Apr 2020 11:20:17 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Andreas Kemnade <andreas@...nade.info>,
        Evgeniy Polyakov <zbr@...emap.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        Adam Ford <aford173@...il.com>,
        "Andrew F . Davis" <afd@...com>, Vignesh R <vigneshr@...com>
Subject: Re: [PATCHv3] w1: omap-hdq: Simplify driver with PM runtime
 autosuspend

* H. Nikolaus Schaller <hns@...delico.com> [200421 18:14]:
> > Am 21.04.2020 um 20:02 schrieb Tony Lindgren <tony@...mide.com>:
> > This is 37xx though, maybe you have 35xx and there's some errata
> > that we're not handling?
> 
> No, it is dm3730 on three different units I have tried.
> 
> > I'm only seeing "2.7. HDQTM/1-Wire® Communication Constraints"
> > for external pull-up resitor in 34xx errata at [0].
> > 
> > I wonder if wrong external pull could cause flakyeness after
> > enabling the hdq module?
> 
> I have checked and we have 10 kOhm pullup to 1.8 V and a 470 Ohm
> series resistor.

OK

> > If nothing else helps, you could try to block idle for hdq
> > module, but I have a feeling that's a workaround for something
> > else.
> 
> Well, what helps is reverting the patch and using the old driver
> (which did work for several years). So I would not assume that
> there is a hardware influence. It seems to be something the new
> driver is doing differently.

Well earlier hdq1w.c did not idle, now it does. If you just want
to keep it enabled like earlier, you can just add something like:

&hdqw1w {
	ti,no-idle;
};

> I need more time to understand and trace this issue on what it
> depends... It may depend on the sequence some other modules are
> loaded and what the user-space (udevd) is doing in the meantime.

Yes would be good to understand what goes wrong here before we
apply the ti,no-idle as that will block SoC deeper idle states.

Regards,

Tony