Re: [PATCH 0/1] Request to review progress decoupling vchiq platform code

Stefan Wahren
2021-06-14T22:06:48Z

Hi,

Am 14.06.21 um 21:32 schrieb Ojaswin Mujoo:
> Greetings,
>
> I'm working on addressing item 10 of the following TODO list:
>
> drivers/staging/vc04-services/interface/TODO
>
> For reference, the task is:
>
> 10) Reorganize file structure: Move char driver to it's own file and join
> both platform files
>
> The cdev is defined alongside with the platform code in vchiq_arm.c. It
> would be nice to completely decouple it from the actual core code. For
> instance to be able to use bcm2835-audio without having /dev/vchiq created.
> One could argue it's better for security reasons or general cleanliness. It
> could even be interesting to create two different kernel modules, something
> the likes of vchiq-core.ko and vchiq-dev.ko. This would also ease the
> upstreaming process.
>
>
> This patch is the first step towards decoupling the platform and the cdev code.
> It moves all the cdev related code from vchiq_arm.c to vchiq_dev.c. However, for
> now, I have aimed to keep the functionality untouched, hence the platform code
> still calls the cdev initialisation function, and isn't truly decoupled yet.
>
> The summary of the changes is as follows:
>
>
> * Definition of functions and variables shared by cdev and platform
> code are moved to vchiq_arm.h while declaration stays in vchiq_arm.c
>
> * Declaration and definition of functions and variables only used by
> cdev code are moved to vchiq_dev.c file.
>
> * Defined vchiq_deregister_chrdev() and vchiq_register_chrdev(..) in
> vchiq_dev.c which handle cdev creation and deletion. They are called by the
> platfrom code during probe().
looks like this should be 3 separate patches. So you have the pure move
at the end.
>
>
> I mainly wanted to put this patch out to see if I have the right idea of the
> task at hand and to ensure I'm heading into the right direction. I would love to
> hear your thoughts and suggestions on this. Once I have some feedback on this, I
> can accordingly work towards a newer version to completely decouple the code.
>
> Lastly, I had some questions related to the the task:
>
> 1. So regarding the following line in the TODO:
>
> "For instance to be able to use bcm2835-audio without having /dev/vchiq
> created."
>
> I was wondering about the possible ways to achieve this. Specifically, I was
> thinking of the following 2 ways:
>
> 1.1 Making a KConfig entry for Cdev creation, like CONFIG_VCHIQ_CDEV, and
> then do something like:
>
> vchiq_probe(..)
> {
> /* platform init code */
>
> #if defined(CONFIG_VCHIQ_CDEV)
>
> /* Call cdev register function */
>
> #endif
> }
A common pattern is to keep the calls, but have "empty" definitions of
the those functions in the header file in case CONFIG_VCHIQ_CDEV is not
defined.
>
> 1.2 The second approach is creating an entirely separate module for the cdev,
> as suggested in the TODO.
>
> So I'm just wondering what the right approach should be?
>
> 2. Second, I currently tested by installing my patches to a pi3 B+ and running
> `cat /dev/vchiq` to compare the output with the original kernel. Also, to
> see if the platform code works without the cdev code, I commented out the
> call to vchiq_register_cdev() and made sure the platform device (and
> children) was registered but the char device was not present. However, I'm
> not sure if these tests are comprehensive enough. What would be the right way
> to test my changes?

Sounds okay, but a functional test is still necessary (tool is provided
by Raspberry Pi OS):

vchiq_test -f 10
vchiq_test -p 10

Regards
Stefan