linux-kernel - Re: [PATCH 2/2] staging: vchiq: Add details to $CONFIG_VCHIQ_CDEV help text

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Message-ID: <fa20cb94-ed73-ea6e-d128-cfb930399af6@i2se.com>
Date:   Wed, 28 Jul 2021 22:39:38 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Ojaswin Mujoo <ojaswin98@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     nsaenz@...nel.org, dan.carpenter@...cle.com, phil@...pberrypi.com,
        linux-arm-kernel@...ts.infradead.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] staging: vchiq: Add details to $CONFIG_VCHIQ_CDEV
 help text

Am 28.07.21 um 22:00 schrieb Ojaswin Mujoo:
> On Wed, Jul 28, 2021 at 08:46:51PM +0200, Greg KH wrote:
>> On Thu, Jul 29, 2021 at 12:07:17AM +0530, Ojaswin Mujoo wrote:
>>> Add some details to the Kconfig definition of $CONFIG_VCHIQ_CDEV to help
>>> make the motive behind it a bit more clear.
>>>
>>> Signed-off-by: Ojaswin Mujoo <ojaswin98@...il.com>
>>> ---
>>>  drivers/staging/vc04_services/Kconfig | 8 ++++++--
>>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/staging/vc04_services/Kconfig b/drivers/staging/vc04_services/Kconfig
>>> index 2b70c37cdd09..cb02d8a4cb74 100644
>>> --- a/drivers/staging/vc04_services/Kconfig
>>> +++ b/drivers/staging/vc04_services/Kconfig
>>> @@ -25,8 +25,12 @@ config VCHIQ_CDEV
>>>  	bool "VCHIQ Character Driver"
>>>  	default y
>>>  	help
>>> -		Enable the creation of VCHIQ character driver to help
>>> -		communicate with the Videocore platform.
>>> +		Enable the creation of VCHIQ character driver to help communicate
>>> +		with the VideoCore platform. The cdev exposes ioctls used by
>>> +		userspace libraries and testing tools to interact with VideoCore.
>>> +		This can be set to 'N' if the VideoCore communication is not needed
>>> +		by userspace but only by other kernel modules (like bcm2835-audio).
>>> +		If not sure, set this to 'Y'.
>> I still do not understand if I need this driver or not, and I have this
>> hardware!  What functionality does this driver accomplish?  What is
>> VideoCore?
> Hey Greg,
>
> I believe I can add this under the CONFIG_BCM2835_VCHIQ config option,
> as that enables the core driver that implements the functions to
> communicate with VideoCore platform? 

Sorry, today i'm too tired to give a good explanation. VideoCore is the
VPU inside the BCM283x SoC. It runs a firmware and VCHIQ provides a way
to communicate with this firmware / VPU. The VCHIQ driver is required to
get access to the audio jack and camera interface (see depending drivers).

Unfortunately i don't have an application list by the hand which uses
the CDEV interface for VCHIQ, please use this link [1] as a starting point.

[1] - https://github.com/raspberrypi/userland

>
> This config option merely adds a cdev which exposes the the core
> driver's functionality to userspace. 
>
> Regards,
> Ojaswin
>> thanks,
>>
>> greg k-h
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
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