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Date:   Thu, 12 Mar 2020 12:44:32 +0100
From:   Alexandre Belloni <alexandre.belloni@bootlin.com>
To:     Wolfram Sang <wsa@the-dreams.de>
Cc:     Luca Ceresoli <luca@lucaceresoli.net>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>,
        Linux I2C <linux-i2c@vger.kernel.org>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
        linux-i3c@lists.infradead.org,
        Kieran Bingham <kieran@ksquared.org.uk>,
        Niklas =?iso-8859-1?Q?S=F6derlund?= 
        <niklas.soderlund@ragnatech.se>, Jacopo Mondi <jacopo@jmondi.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Vladimir Zapolskiy <vz@mleia.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>
Subject: Re: [RFC PATCH 3/7] i2c: allow DT nodes without 'compatible'
Message-ID: <20200312114432.GA3384@piout.net>
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On 12/03/2020 12:19:51+0100, Wolfram Sang wrote:
> > Clearly this does not fit the case reported by Alexandre: a device
> > having a driver which is known to be badly buggy, so we don't want to
> > instantiate it. But again, this should not affect DT as it is not
> > describing the HW, but only an implementation detail. Probably disabling
> > or blacklisting the driver would be a better option there?
> 
> "Fixing the driver" is the first thing coming to my mind ;) But yeah,
> blacklisting would be another good solution. With only the information
> above, DT is not the right place to fix a broken driver.
> 

To be clear, the driver is working properly but the HW isn't. It is a
PMIC and we need to avoid linux talking to it so the PMIC doesn't end up
killing the bus.

We end up with a node properly described in the device tree but with
status = "disabled". The relevance to the discussion was that you know
what is there and you want to avoid using its address.

See the pmic node on i2c1 in arch/arm/boot/dts/at91-sama5d3_xplained.dts
for what I'm referring to.

> > My apologies to Wolfram, I appreciate a lot the effort you are doing,
> > but before reviewing this patch I have never realized what I tried to
> > explain above.
> 
> All good, Luca! Talking over code usually brings in viewpoints which
> have been missed so far. This is expected. Actually, I am very happy to
> have this discussion!
> 
> All the best,
> 
>    Wolfram
> 


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com