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 16:29:32 -0700
From:   sathyanarayanan kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Hans de Goede <hdegoede@...hat.com>, Peter Rosin <peda@...ntia.se>,
        Andy Shevchenko <andy.shevchenko@...il.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 05/31/2017 11:27 AM, Hans de Goede wrote:
> 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)
I think maintaining unique mux control names across all mux devices will be
bit difficult to maintain. Unless its auto created as Hans mentioned using
device name + chip index  + control index.

or , we can have unique names for mux-chips and get mux-control handles 
based
on index numbers. This should at least reduce some of the search time.

mux_control_get("mux chip name",  index)
>
>
> 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
>
>
>

-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer