Re: [PATCH v8 1/5] staging: vc04_services: vchiq_arm: Add new bus type and device type

Umang Jain
2023-07-03T16:15:31Z

Hi Greg,

(resending because it got bounced off a few lists due a line a copied
with HTML tag..)

On 7/3/23 3:28 PM, Greg KH wrote:
> On Tue, Jun 27, 2023 at 10:16:24PM +0200, 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 getting
>> registered as platform drivers. This is not correct and a blatant
>> abuse of platform device/driver.
>>
>> Add a new bus type, vchiq_bus_type and device type (struct vchiq_device)
>> which will be used to migrate child devices that the vchiq interfaces
>> creates/registers from the platform device/driver.
>>
>> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
>> ---
>> drivers/staging/vc04_services/Makefile | 1 +
>> .../interface/vchiq_arm/vchiq_device.c | 78 +++++++++++++++++++
>> .../interface/vchiq_arm/vchiq_device.h | 43 ++++++++++
>> 3 files changed, 122 insertions(+)
>> create mode 100644 drivers/staging/vc04_services/interface/vchiq_arm/vchiq_device.c
>> create mode 100644 drivers/staging/vc04_services/interface/vchiq_arm/vchiq_device.h
>>
>> diff --git a/drivers/staging/vc04_services/Makefile b/drivers/staging/vc04_services/Makefile
>> index 44794bdf6173..2d071e55e175 100644
>> --- a/drivers/staging/vc04_services/Makefile
>> +++ b/drivers/staging/vc04_services/Makefile
>> @@ -5,6 +5,7 @@ vchiq-objs := \
>> interface/vchiq_arm/vchiq_core.o \
>> interface/vchiq_arm/vchiq_arm.o \
>> interface/vchiq_arm/vchiq_debugfs.o \
>> + interface/vchiq_arm/vchiq_device.o \
>> interface/vchiq_arm/vchiq_connected.o \
>>
>> ifdef CONFIG_VCHIQ_CDEV
>> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_device.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_device.c
>> new file mode 100644
>> index 000000000000..dff312e9735c
>> --- /dev/null
>> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_device.c
>> @@ -0,0 +1,78 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * vchiq_device.c - VCHIQ generic device and bus-type
>> + *
>> + * Copyright (c) 2023 Ideas On Board Oy
>> + */
>> +
>> +#include <linux/device/bus.h>
>> +#include <linux/slab.h>
>> +#include <linux/string.h>
>> +
>> +#include "vchiq_device.h"
>> +
>> +static int vchiq_bus_type_match(struct device *dev, struct device_driver *drv);
>> +
>> +struct bus_type vchiq_bus_type = {
>> + .name = "vchiq-bus",
>> + .match = vchiq_bus_type_match,
>> +};
>> +
>> +static int vchiq_bus_type_match(struct device *dev, struct device_driver *drv)
>> +{
>> + if (dev->bus == &vchiq_bus_type &&
>> + strcmp(dev_name(dev), drv->name) == 0)
>> + return 1;
>> + return 0;
>> +}
>> +
>> +static void vchiq_device_release(struct device *dev)
>> +{
>> + struct vchiq_device *device;
>> +
>> + device = container_of(dev, struct vchiq_device, dev);
>> + kfree(device);
>> +}
>> +
>> +int vchiq_device_register(struct device *parent, const char *name)
>> +{
>> + struct vchiq_device *device = NULL;
> No need to set this to NULL.
>
>> + int ret;
>> +
>> + device = kzalloc(sizeof(*device), GFP_KERNEL);
>> + if (!device)
>> + return -ENOMEM;
>> +
>> + device->dev.init_name = name;
>> + device->dev.parent = parent;
>> + device->dev.bus = &vchiq_bus_type;
>> + device->dev.release = vchiq_device_release;
>> +
>> + ret = device_register(&device->dev);
>> + if (ret) {
>> + put_device(&device->dev);
>> + return -EINVAL;
> Why not return the error given to you?
>
>> + }
>> +
>> + return 0;
> You create a new device, shouldn't you return it? How is it going to be
> looked up again?

So I haven't come across usage of the device other than unregistered
right now. If you look at the platform_device static instances of
bcm2835_camera, bcm2835-audio, they are also just used for unregistering
the devices only.

So for unregistering devices on vchiq_bus - I am using the

bus_for_each_dev(&vchiq_bus_type, NULL, NULL, vchiq_device_unregister);

in patch 3/5.

So basically I can return the instances right now, but there would be no
user of those instances.
>
>> +}
>> +
>> +int vchiq_device_unregister(struct device *dev, void *data)
> You should be passing in a sruct vchiq_device *device here, right?
>
> And why the void pointer you do nothing with?

ack
>
>
>> +{
>> + device_unregister(dev);
>> + return 0;
>> +}
> No need to export this?

In the previous reviews you mentioned not to export it. The
vchiq_bus_type is internal to the vchiq_driver to register it's child
devices. I don't think any other module will be using this bus directly?
Maybe I'm mistaken?
>
> thanks,
>
> greg k-h