linux-kernel - Re: [PATCH 5/6 v2] mtd: rawnand: ams-delta: use GPIO lookup table

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Message-ID: <20180604115543.3be75717@bbrezillon>
Date:   Mon, 4 Jun 2018 11:55:43 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>
Cc:     Richard Weinberger <richard@....at>,
        H Hartley Sweeten <hsweeten@...ionengravers.com>,
        Tony Lindgren <tony@...mide.com>, linux-kernel@...r.kernel.org,
        Marek Vasut <marek.vasut@...il.com>,
        Krzysztof Halasa <khalasa@...p.pl>,
        Shreeya Patel <shreeya.patel23498@...il.com>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        linux-mtd@...ts.infradead.org
Subject: Re: [PATCH 5/6 v2] mtd: rawnand: ams-delta: use GPIO lookup table

On Wed, 30 May 2018 22:39:03 +0200
Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:

> On Wednesday, May 30, 2018 7:52:20 PM CEST Boris Brezillon wrote:
> > On Wed, 30 May 2018 19:43:09 +0200
> > 
> > Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:  
> > > On Wednesday, May 30, 2018 11:05:00 AM CEST Boris Brezillon wrote:  
> > > > Hi Janusz,  
> > > 
> > > Hi Boris,
> > >   
> > > > On Sat, 26 May 2018 00:20:45 +0200
> > > > 
> > > > Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:  
> > > > > ...
> > > > > Changes since v1:
> > > > > - fix handling of devm_gpiod_get_optional() return values - thanks to
> > > > > 
> > > > >   Andy Shevchenko.  
> > > > 
> > > > Can you put the changelog after the "---" separator so that it does not
> > > > appear in the final commit message?  
> > > 
> > > Yes, sure, sorry for that.
> > >   
> > > > > +err_gpiod:
> > > > > +	if (err == -ENODEV || err == -ENOENT)
> > > > > +		err = -EPROBE_DEFER;  
> > > > 
> > > > Hm, isn't it better to make gpiod_find() return ERR_PTR(-EPROBE_DEFER)
> > > > here [1]? At least, ENOENT should not be turned into EPROBE_DEFER,
> > > > because it's returned when there's no entry matching the requested gpio
> > > > in the lookup table, and deferring the probe won't solve this problem.  
> > > 
> > > ENOENT is also returned when no matching lookup table is found. That may
> > > happen if consumer dev_name stored in the table differs from dev_name
> > > assigned to the consumer by its bus, the platform bus in this case. For
> > > that reason I think the consumer dev_name should be initialized in the
> > > table after the device is registered, when its actual dev_name can be
> > > obtained. If that device registration happens after the driver is already
> > > registered, e.g., at late_initcall, the device is probed before its
> > > lookup table is ready. For that reason returning EPROBE_DEFER seems
> > > better to me even in the ENOENT case.  
> > Sorry, I don't get it. Aren't GPIO lookup tables supposed to be declared
> > in board files, especially if the GPIO is used by a platform device?
> > When would you have a lookup table registered later in the init/boot
> > process?  
> 
> When e.g. I'd like to register my GPIO consumer platform device at 
> late_initcall for some reason, and I'm not sure what exact dev_name my 
> consomer will be registered with by the platform bus.

You should know the name before the device is registered.

> In that case I think I 
> should assign dev_name to the lookup table after the consumer device is 
> registered and its exact dev_name can be obtained, then register the table,

I'm pretty sure it's not supposed to work like that. Resources attached
to a device should be defined before the device is registered, not
after, simply because when you call platform_device_register(), the
device might be directly bind to the driver before the
platform_device_register() calls return, and the driver will fail to
probe the device if it doesn't find the GPIO it needs.