linux-kernel - Re: [PATCH v3] staging: vc04_services: vchiq: Register devices with a custom bus

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Date:   Tue, 17 Jan 2023 19:21:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Umang Jain <umang.jain@...asonboard.com>
Cc:     linux-staging@...ts.linux.dev,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Stefan Wahren <stefan.wahren@...e.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Adrien Thierry <athierry@...hat.com>,
        Dan Carpenter <error27@...il.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Phil Elwell <phil@...pberrypi.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v3] staging: vc04_services: vchiq: Register devices with
 a custom bus_type

On Wed, Jan 11, 2023 at 02:30:29PM +0530, Umang Jain wrote:
> The devices that the vchiq interface registers(bcm2835-audio,
> bcm2835-camera) are implemented and exposed by the VC04 firmware.
> The device tree describes the VC04 itself with the resources
> required to communicate with it through a mailbox interface. However,
> the vchiq interface registers these devices as platform devices. This
> also means the specific drivers for these devices are also getting
> registered as platform drivers. This is not correct and a blatant
> abuse of platform device/driver.
> 
> Replace the platform device/driver model with a standard device driver
> model. A custom bus_type, vchiq_bus_type, is created in the vchiq
> interface which matches the devices to their specific device drivers
> thereby, establishing driver binding. A struct vchiq_device wraps the
> struct device for each device being registered on the bus by the vchiq
> interface.
> 
> Each device registered will expose a 'name' read-only device attribute
> in sysfs (/sys/bus/vchiq-bus/devices). New devices and drivers can be
> added by registering on vchiq_bus_type and adding a corresponding
> device name entry in the static list of devices, vchiq_devices. There
> is currently no way to enumerate the VCHIQ devices that are available
> from the firmware.
> 
> Signed-off-by: Umang Jain <umang.jain@...asonboard.com>
> ---
> Changes in v3:
> - Rework entirely to replace platform devices/driver model
> 
> -v2:
> https://lore.kernel.org/all/20221222191500.515795-1-umang.jain@ideasonboard.com/
> 
> -v1:
> https://lore.kernel.org/all/20221220084404.19280-1-umang.jain@ideasonboard.com/
> 
> - Developed on top of:
> [PATCH v3 0/7] staging: vc04_services: Remove custom return values
> 
> ---
>  .../vc04_services/bcm2835-audio/Makefile      |   5 +-
>  .../vc04_services/bcm2835-audio/bcm2835.c     |  19 ++-
>  .../vc04_services/bcm2835-camera/Makefile     |   2 +
>  .../bcm2835-camera/bcm2835-camera.c           |  17 ++-
>  .../interface/vchiq_arm/vchiq_arm.c           | 121 +++++++++++++++---
>  .../interface/vchiq_arm/vchiq_arm.h           |   1 +
>  6 files changed, 123 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/staging/vc04_services/bcm2835-audio/Makefile b/drivers/staging/vc04_services/bcm2835-audio/Makefile
> index d59fe4dde615..4801467be58a 100644
> --- a/drivers/staging/vc04_services/bcm2835-audio/Makefile
> +++ b/drivers/staging/vc04_services/bcm2835-audio/Makefile
> @@ -2,4 +2,7 @@
>  obj-$(CONFIG_SND_BCM2835)	+= snd-bcm2835.o
>  snd-bcm2835-objs		:= bcm2835.o bcm2835-ctl.o bcm2835-pcm.o bcm2835-vchiq.o
>  
> -ccflags-y += -I $(srctree)/$(src)/../include -D__VCCOREVER__=0x04000000
> +ccflags-y += \
> +	-I $(srctree)/$(src)/../include \
> +	-I $(srctree)/$(src)/../interface/vchiq_arm \

Please never add new -I entries, as that can break the build when you
only want to build a subdirectory.  Just use the "../" in the .c files
instead.

While you are not responsible for the original one here, please never
add a new one.

And, you can work to get rid of the current addition as well, that
should be done sooner rather than later anyway.

thanks,

greg k-h