linux-kernel - RE: [PATCH v9 5/6] usb:cdns3 Add Cadence USB3 DRD Driver

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Date:   Wed, 10 Jul 2019 08:25:08 +0000
From:   Pawel Laszczak <pawell@...ence.com>
To:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "heikki.krogerus@...ux.intel.com" <heikki.krogerus@...ux.intel.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "rogerq@...com" <rogerq@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jbergsagel@...com" <jbergsagel@...com>,
        "nsekhar@...com" <nsekhar@...com>, "nm@...com" <nm@...com>,
        Suresh Punnoose <sureshp@...ence.com>,
        "peter.chen@....com" <peter.chen@....com>,
        Jayshri Dajiram Pawar <jpawar@...ence.com>,
        Rahul Kumar <kurahul@...ence.com>
Subject: RE: [PATCH v9 5/6] usb:cdns3 Add Cadence USB3 DRD Driver

Hi Felipe

>>> +
>>> +static int cdns3_idle_init(struct cdns3 *cdns)
>>> +{
>>> +	struct cdns3_role_driver *rdrv;
>>> +
>>> +	rdrv = devm_kzalloc(cdns->dev, sizeof(*rdrv), GFP_KERNEL);
>>> +	if (!rdrv)
>>> +		return -ENOMEM;
>>> +
>>> +	rdrv->start = cdns3_idle_role_start;
>>> +	rdrv->stop = cdns3_idle_role_stop;
>>> +	rdrv->state = CDNS3_ROLE_STATE_INACTIVE;
>>> +	rdrv->suspend = NULL;
>>> +	rdrv->resume = NULL;
>>> +	rdrv->name = "idle";
>>
>>why don't you use the mux framework for this? This looks a bit fishy
>>too. Why do you have your own driver registration structure for your
>>driver only?
>>
>
>I assume you mean interface defined in include/linux/usb/role.h.
>It's quite new framework and probably was added after I've start implementing cdns3 driver.
>At first glance it's look that I could use it.

I've started integrating driver with role switch framework.  

Even if I use role switch interface , I still need this internal driver registration. 
It's convenient to use fallowing structure. 

struct cdns3_role_driver {
	int (*start)(struct cdns3 *cdns);
	void (*stop)(struct cdns3 *cdns);
	int (*suspend)(struct cdns3 *cdns, bool do_wakeup);
	int (*resume)(struct cdns3 *cdns, bool hibernated);
	const char *name;
#define CDNS3_ROLE_STATE_INACTIVE	0
#define CDNS3_ROLE_STATE_ACTIVE		1
	int state;
};

Driver can supports: only Host, only Device or DRD - depending on configuration.

If current configuration support only Host then driver assigns:
	rdrv_host->start	= __cdns3_host_init;
	rdrv_host->stop	= cdns3_host_exit;

	cdns->roles[CDNS3_ROLE_HOST]  = 	rdrv_host
	cdns->roles[CDNS3_ROLE_GADGET	= NULL;
if support only Device then:
	rdrv_dev->start	= __cdns3_ gadget _init;
	rdrv_dev->stop	= cdns3_ gadget _exit;
	cdns->roles[CDNS3_ROLE_HOST]	= NULL;
for DRD:
	cdns->roles[CDNS3_ROLE_HOST = rdrv_host;
	cdns->roles[CDNS3_ROLE_GADGET] = rdrv_dev;

So for DRD we will have both filled, but for only Device or Host we 
will have filled single element of array. 

With such array we can easily start/stop role by 
	if (!cdns->roles[role])
		not supported by configuration.
	else
		cdns->roles[role]->start / cdns->roles[role]->stop

I don't need any extra: switch instruction or #ifdef statement. 

The name cdns3_role_driver can be misleading. 
Driver doesn't register the driver but rather the interface to Device/Host. 

Maybe I should change this name to  cdns3_role_interface or cdns3_role_action ?

Now I have my private enum:
enum cdns3_roles {
	CDNS3_ROLE_IDLE = 0,
	CDNS3_ROLE_HOST,
	CDNS3_ROLE_GADGET,
	CDNS3_ROLE_END,
};

I think I could replace it with usb_role. I need one extra state for IDLE but
Instead of CDNS3_ROLE_IDLE I can use USB_ROLE_NONE.

It should little simplify the driver and improve readability. 

Do you have any comments or suggestion ?

Cheers, 
Pawel

>
>>> +
>>> +	cdns->roles[CDNS3_ROLE_IDLE] = rdrv;
>>> +
>>> +	return 0;
>>> +}
>>> +