linux-kernel - Re: [RFC PATCHv2] usb: USB Type-C Connector Class

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Message-ID: <5745A4A2.9060502@roeck-us.net>
Date:	Wed, 25 May 2016 06:12:02 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Oliver Neukum <oneukum@...e.com>,
	Rajaram R <rajaram.officemail@...il.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class

On 05/25/2016 04:30 AM, Heikki Krogerus wrote:
> Hi,
>
> On Tue, May 24, 2016 at 06:42:09AM -0700, Guenter Roeck wrote:
>>> +struct typec_capability {
>>> +	enum typec_data_role	role;
>>> +	unsigned int		usb_pd:1;
>>> +	struct typec_altmode	*alt_modes;
>>> +	unsigned int		audio_accessory:1;
>>> +	unsigned int		debug_accessory:1;
>>> +
>>> +	int			(*fix_role)(struct typec_port *,
>>> +					    enum typec_data_role);
>>> +
>>> +	int			(*dr_swap)(struct typec_port *);
>>> +	int			(*pr_swap)(struct typec_port *);
>>> +	int			(*vconn_swap)(struct typec_port *);
>>> +
>>
>> The function parameter in those calls is all but useless to the caller.
>> It needs to store the typec_port returned from typec_register(), create a
>> list of ports, and then search through this list each time one of the
>> functions is called. This is quite expensive for no good reason.
>>
>> Previously, with typec_port exported, the called code could use the stored
>> caps pointer to map to its internal data structures. This is no longer
>> possible.
>
> True, the API now is in practice broken.
>
>> I think it would be useful to provide a better means for the called function
>> to identify its context. Maybe provide a pointer to the private data in
>> the registration function and use it as parameter in the callback functions ?
>
> Sounds reasonable.
>

I'll send a follow-up patch hopefully later today which fixes all the problems
I have found so far.

Guenter