finding out the attached device current requirement

finding out the attached device current requirement

[Pavan Kondeti]

Hi

I am adding ACA (Accessory Charger Adapter) detection support for MSM
OTG driver. Battery charging spec introduced ACA to facilitate charging
when acting as a host. The host does not have to supply power on VBUS
when ACA is connected. Host device can also draw some amount of current.
The amount of current is determined by subtracting the attached
peripheral current requirement from the charger rating current. I am
looking for a way to find out the attached peripheral's current
requirement. We already DEVICE_ADD and DEVICE_REMOVE notifications. But
we can not assume that device will be configured by the time DEVICE_ADD
notification is sent. And also there is a possibility that configuration
change request from use. Is it a good idea to add DEVICE_CONFIG_CHANGE
notification to solve this problem?

Thanks,
Pavan

-- 
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: finding out the attached device current requirement

[Felipe Balbi]

On Thu, Mar 03, 2011 at 02:22:34PM +0530, Pavan Kondeti wrote:
> Hi
> 
> I am adding ACA (Accessory Charger Adapter) detection support for MSM
> OTG driver. Battery charging spec introduced ACA to facilitate charging
> when acting as a host. The host does not have to supply power on VBUS
> when ACA is connected. Host device can also draw some amount of current.
> The amount of current is determined by subtracting the attached
> peripheral current requirement from the charger rating current. I am
> looking for a way to find out the attached peripheral's current
> requirement. We already DEVICE_ADD and DEVICE_REMOVE notifications. But

bMaxPower from the device descriptor ??

-- 
balbi

Re: finding out the attached device current requirement

[Pavan Kondeti]

On 3/3/2011 3:15 PM, Felipe Balbi wrote:
> On Thu, Mar 03, 2011 at 02:22:34PM +0530, Pavan Kondeti wrote:
>> Hi
>>
>> I am adding ACA (Accessory Charger Adapter) detection support for MSM
>> OTG driver. Battery charging spec introduced ACA to facilitate charging
>> when acting as a host. The host does not have to supply power on VBUS
>> when ACA is connected. Host device can also draw some amount of current.
>> The amount of current is determined by subtracting the attached
>> peripheral current requirement from the charger rating current. I am
>> looking for a way to find out the attached peripheral's current
>> requirement. We already DEVICE_ADD and DEVICE_REMOVE notifications. But
> 
> bMaxPower from the device descriptor ??
> 
You are referring to bMaxPower in Configuration descriptor right? When a
multi configuration device is connected, configuration can be changed by
user at any time. The same can also be possible with a user claimed
port. So I am looking for a notification from USB core when a
SET_CONFIGURATION request is sent to a device connected on the root hub.
I will reduce my power (ACA rating current - bMaxpower of the config
being selected) upon this notification.

Thanks,
Pavan

-- 
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.