linux-kernel - Re: [PATCH 4/6] bus: add driver for the Technologic Systems NBUS

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Date:   Fri, 3 Feb 2017 14:51:15 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Sebastien Bourdelin <sebastien.bourdelin@...oirfairelinux.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-watchdog@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        kernel <kernel@...oirfairelinux.com>,
        Mark Featherston <mark@...eddedarm.com>, kris@...eddedarm.com,
        Simon Horman <horms+renesas@...ge.net.au>,
        Thierry Reding <treding@...dia.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Sascha Hauer <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck <wim@...ana.be>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        damien.riegel@...oirfairelinux.com,
        Lucile Quirion <lucile.quirion@...oirfairelinux.com>,
        Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
        "Suzuki K. Poulose" <suzuki.poulose@....com>,
        Will Deacon <will.deacon@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH 4/6] bus: add driver for the Technologic Systems NBUS

On Wed, Feb 1, 2017 at 8:56 PM, Sebastien Bourdelin
<sebastien.bourdelin@...oirfairelinux.com> wrote:
> On 12/30/2016 02:58 AM, Linus Walleij wrote:

>>> +static struct ts_nbus *ts_nbus;
>>
>> Nopes. No singletons please.
>>
>> Use the state container pattern:
>> Documentation/driver-model/design-patterns.txt
>
> I understand the idea but have problem to find a good way to implement it.
>
> Other drivers using the NBUS which are child nodes in the device tree
> will use the ts_nbus_write() and ts_nbus_read() functions, it means these
> drivers should have a pointer to the allocated ts_nbus and pass it to
> the write() and read() functions as an argument if i'm not using a
> singleton here.
> But i'm lacking knowledge on how to properly share this pointer when
> initializing the NBUS driver with the child nodes.

Your child nodes I guess will be instatiated as devices as well.

These devices will have the NBUS driver as .parent in their
struct device I guess. Else the design of this bus is tilted.

If the NBUS driver use dev_set_drvdata(dev, state_container_cookie)
the children can use dev_get_drvdata(dev->parent); to get a pointer to
the same cookie.

The subdrivers don't even need to know the members of the state
container as long as you're just passing a pointer to it. It's
enough if you forward-declare it as a "pointer to some struct":

struct foo;

{
   struct foo *fooptr = dev_get_drvdata(dev->parent);
   write(fooptr, 0x10);

etc

Yours,
Linus Walleij