linux-kernel - Re: [PATCH v3 04/10] usb: dwc3: use quirks to know if a particualr platform doesn't have PHY

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Message-ID: <52A56DA1.1010808@ti.com>
Date:	Mon, 9 Dec 2013 12:43:37 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
CC:	<balbi@...com>, <bcousson@...libre.com>,
	<devicetree@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-usb@...r.kernel.org>, <rob.herring@...xeda.com>,
	<pawel.moll@....com>, <mark.rutland@....com>,
	<swarren@...dotorg.org>, <ijc+devicetree@...lion.org.uk>,
	<rob@...dley.net>, <tony@...mide.com>, <linux@....linux.org.uk>,
	<gregkh@...uxfoundation.org>, <grant.likely@...aro.org>,
	<s.nawrocki@...sung.com>, <galak@...eaurora.org>
Subject: Re: [PATCH v3 04/10] usb: dwc3: use quirks to know if a particualr
 platform doesn't have PHY

Hi,

On Thursday 05 December 2013 01:28 PM, Heikki Krogerus wrote:
> Hi,
>
> On Thu, Dec 05, 2013 at 12:04:46PM +0530, Kishon Vijay Abraham I wrote:
>> On Wednesday 04 December 2013 08:10 PM, Heikki Krogerus wrote:
>>> On Mon, Nov 25, 2013 at 03:31:24PM +0530, Kishon Vijay Abraham I wrote:
>>>> There can be systems which does not have an external phy, so get
>>>> phy only if no quirks are added that indicates the PHY is not present.
>>>> Introduced two quirk flags to indicate the *absence* of usb2 phy and
>>>> usb3 phy. Also remove checking if return value is -ENXIO since it's now
>>>> changed to always enable usb_phy layer.
>>>
>>> Can you guys explain why is something like this needed? Like with
>>> clocks and gpios, the device drivers shouldn't need to care any more
>>> if the platform has the phys or not. -ENODEV tells you your platform
>>
>> Shouldn't we report if a particular platform needs a PHY and not able to get
>> it. How will a user know if a particular controller is not working because it's
>> not able to get and initialize the PHYs? Don't you think in such cases it's
>> better to fail (and return from probe) because the controller will not work
>> anyway without the PHY?
>
> My point is that you do not need to separately tell this to the driver
> like you do with the quirks (if you did, then you would need to fix
> your framework and not hack the drivers).
>
> Like I said, ENODEV tells you that there is no phy on this platform
> for you, allowing you to safely continue. If your phy driver is not
> loaded, the framework already returns EPROBE_DEFER, right. Any other

right. but that doesn't consider broken dt data. With quirks we'll able 
to tell if a controller in a particular platform has PHY or not without 
depending on the dt data.
> error when getting the phy you can consider critical. They are the
> errors telling you that you do need a phy on this platform, but
> something actually went wrong when getting it.
Not on all scenarios though :-s

Thanks
Kishon
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