linux-kernel - Re: [PATCH v1 1/1] mux: mux-intel-usb: Add Intel USB Multiplexer driver

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Date:   Wed, 31 May 2017 20:27:28 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Peter Rosin <peda@...ntia.se>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "Krogerus, Heikki" <heikki.krogerus@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sathyanarayanan Kuppuswamy Natarajan <sathyaosid@...il.com>
Subject: Re: [PATCH v1 1/1] mux: mux-intel-usb: Add Intel USB Multiplexer
 driver

Hi,

On 31-05-17 17:30, Peter Rosin wrote:
> On 2017-05-31 16:18, Hans de Goede wrote:
>> Hi,
>>
>> On 31-05-17 15:05, Peter Rosin wrote:
>>> On 2017-05-31 14:21, Hans de Goede wrote:
>>>> actually this is the first time I hear about a mux framework
>>>> at all. Is there a git tree with the patches for this somewhere ?
>>>
>>> https://gitlab.com/peda-linux/mux.git in the "mux" branch.
>>>
>>> Series posted here:
>>> https://lkml.org/lkml/2017/5/14/160
>>
>> Thank you.
>>
>> I see that mux_control_get() currently relies on devicetree describing
>> the mux, that is not going to work on non devicetree platforms like
>> x86 where the relation typically is not described ad all (*) ?
> 
> Yes, I'm aware of this.

Ok, good.

> I wanted to keep things simple. Also, see
> my reply on the other branch of this discussion.
> 
> https://lkml.org/lkml/2017/5/31/58
> 
>> Typically there would be a global list of mux_controls maintained
>> by mux_[de]register and then mux_control_get() would walk this list
>> until it finds a matching name. The names to register would then be
>> passed in by platform data/code when registering and likewise the
>> consumer would be passed a unique name to pass into mux_control_get()
>> through platform data / code, would that work for you ?
>>
>> Note one option would be to set the names to use when registering
>> a mux chip through device_properties, this is what the power-supply
>> subsys is currently doing more or less.
> 
> I had this lose plan to match by the struct device name, but if that
> is not working the above seems fine too...

There are 2 problems with using dev_name() :

1) dev_name() will be coupled to the mux_chip and one mux_chip may
have multiple controllers (you could add a number postfix to work
around this)

2) The caller of mux_control_get() wants a fixed name, where as
dev_name is not always fixed, e.g. with mux-chips which communicate
via i2c it is something like 7-0064 where 7 is the i2c bus-number
which depends on probe ordering and thus may not even be the same
every boot.

Regards,

Hans