linux-kernel - Re: [PATCH 2/6] phy: improved lookup method

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Date:	Mon, 29 Sep 2014 11:58:15 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Felipe Balbi <balbi@...com>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 2/6] phy: improved lookup method



On Thursday 25 September 2014 12:30 PM, Heikki Krogerus wrote:
>>>>>>>>> Assume you have 2 phys in your system..
>>>>>>>>> static struct phy_lookup usb_lookup = {
>>>>>>>>> 	.phy_name	= "phy-usb.0",
>>>>>>>>> 	.dev_id		= "usb.0",
>>>>>>>>> 	.con_id		= "usb",
>>>>>>>>> };
>>>>>>>>>
>>>>>>>>> static struct phy_lookup sata_lookup = {
>>>>>>>>> 	.phy_name	= "sata-usb.1",
>>>>>>>>> 	.dev_id		= "sata.0",
>>>>>>>>> 	.con_id		= "sata",
>>>>>>>>> };
>>>>>>>>>
>>>>>>>>> First you do modprobe phy-usb, the probe of USB PHY driver gets invoked and it
>>>>>>>>> creates the PHY. The phy-core will find a free id (now it will be 0) and then
>>>>>>>>> name the phy as phy-usb.0.
>>>>>>>>> Then with modprobe phy-sata, the phy-core will create phy-sata.1.
>>>>>>>>>
>>>>>>>>> This is an ideal case where the .phy_name in phy_lookup matches.
>>>>>>>>>
>>>>>>>>> Consider if the order is flipped and the user does modprobe phy-sata first. The
>>>>>>>>> phy_names won't match anymore (the sata phy device name would be "sata-usb.0").
>>>>>>>
>>>>>>> Actually, I don't think there would be this problem if we used the
>>>>>>> name of the actual device which is the parent of phy devices, right?
>>>>>>
>>>>>> hmm.. but if the parent is a multi-phy phy provider (like pipe3 PHY driver), we
>>>>>> might end up with the same problem.
>>>>>
>>>>> I'm not completely sure what you mean? If you are talking about
>>>>> platforms with multiple instances of a single phy, I don't see how
>>>>> there could ever be a scenario where we did not know the order in
>>>>> which they were enumerated. Can you give an example again?
>>>>
>>>> If a single IP implements multiple PHYs (phy-miphy365x.c in linux-phy next),
>>>> the parent for all the phy devices would be the same.
> 
> Hold on...
> 
> Let's take a step back here. Where could we actually have a scenario
> where the phy device, the dev_id (consumer) and the con_id would all
> be the same? There can't be such a case.
> 
> It's not like you could ever have a driver requesting multiple phys
> with the same con_id. You would just get the same phy handle even if
> you used dt.
> 
>         phy1 = phy_get(dev, "phy");
>         ...
>         phy2 = phy_get(dev, "phy");
> 
> And if the drivers requesting those phys are different, your consumers
> are different.

sounds right to me.

Cheers
Kishon
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