linux-kernel - Re: [PATCH v2 1/2] extcon: Add extcon_set_cable_line_state() to inform the additional state of external connectors

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Message-ID: <1432803731.2348.28.camel@mm-sol.com>
Date:	Thu, 28 May 2015 12:02:11 +0300
From:	"Ivan T. Ivanov" <iivanov@...sol.com>
To:	cw00.choi@...sung.com
Cc:	Roger Quadros <rogerq@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Robert Baldyga <r.baldyga@...sung.com>,
	Peter Chen <peter.chen@...escale.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Felipe Balbi <balbi@...com>,
	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>
Subject: Re: [PATCH v2 1/2] extcon: Add extcon_set_cable_line_state() to
 inform the additional state of external connectors


Hi Chanwoo, 

On Thu, 2015-05-28 at 00:06 +0900, Chanwoo Choi wrote:
> On Wed, May 27, 2015 at 11:38 PM, Roger Quadros <rogerq@...com> wrote:
> > Chanwoo,
> > 
> > On 27/05/15 15:15, Chanwoo Choi wrote:
> > > This patch adds the extcon_set_cable_line_state() function to inform
> > > the additional state of each external connector and 'enum
> > > extcon_line_state'
> > > enumeration which include the specific states of each external connector.
> > > 
> > > The each external connector might need the different line state. So,
> > > current
> > > 'extcon_line_state' enumeration contains the specific state for USB as
> > > following:
> > > 
> > > - Following the state mean the state of both ID and VBUS line for USB:
> > > enum extcon_line_state {
> > >         EXTCON_USB_ID_LOW       = BIT(1),       /* ID line is low. */
> > >         EXTCON_USB_ID_HIGH      = BIT(2),       /* ID line is high. */
> > 
> > 
> > ID_LOW and ID_HIGH cannot happen simultaneously so they can use the same bit
> > position.
> > if the bit is set means it is high, if it is cleared means it is low.
> 
> These are the notifier event. So, extcon_line_state have to include
> each event for both low or high state of ID.
> because the extcon consumer driver using the
> extcon_register_notifier() need the each event to distinguish the type
> of event.
> 
> > >         EXTCON_USB_VBUS_LOW     = BIT(3),       /* VBUS line is low. */
> > >         EXTCON_USB_VBUS_HIGH    = BIT(4),       /* VBUS line is high. */
> > 
> > 
> > same here.
> 
> ditto.
> 
> > enum doesn't look like the right type for extcon_line_state as it is more of
> > a bitmask.
> 
> Why? I prefer to use the enum if there are no problem.

I do agree with Roger.
 
> > > 
> > > +enum extcon_line_state {
> > > +       /* Following two definition are used for whether external
> > > connectors
> > > +        * is attached or detached. */
> > > +       EXTCON_DETACHED         = 0x0,
> > > +       EXTCON_ATTACHED         = 0x1,
> > > +
> > > +       /* Following states are only used for EXTCON_USB. */
> > > +       EXTCON_USB_ID_LOW       = BIT(1),       /* ID line is low. */
> > > +       EXTCON_USB_ID_HIGH      = BIT(2),       /* ID line is high. */
> > > +       EXTCON_USB_VBUS_LOW     = BIT(3),       /* VBUS line is low. */
> > > +       EXTCON_USB_VBUS_HIGH    = BIT(4),       /* VBUS line is high. */
> > > +};
> > 
> > 
> > Why do you use enum? How about the following bit definitions for line state.
> > 
> > #define EXTCON_ATTACHED_DETACHED_BIT    BIT(0)
> > #define EXTCON_USB_ID_BIT               BIT(1)
> > #define EXTCON_USB_VBUS_BIT             BIT(2)
> > ...
> > 
> > code must check if appropriate bit is set or cleared to get the high/low
> > state.
> 
> I answer about it on upper.
> 

Funny. We can use the one bit for DETACHED/ATTACHED, but we
can not use the one bit for LOW/HIGH?

Regards,
Ivan
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