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Message-ID: <26e85324-ac50-807d-d6ee-1fe04396d69e@ideasonboard.com>
Date:   Fri, 20 Jan 2023 16:26:00 +0530
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Subject: Re: [PATCH v5 6/6] staging: vc04_services: vchiq: Register devices
 with a custom bus_type
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     linux-staging@lists.linux.dev,
        linux-rpi-kernel@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Stefan Wahren <stefan.wahren@i2se.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Adrien Thierry <athierry@redhat.com>,
        Dan Carpenter <error27@gmail.com>,
        Dave Stevenson <dave.stevenson@raspberrypi.com>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>,
        Paul Elder <paul.elder@ideasonboard.com>
References: <20230119115503.268693-1-umang.jain@ideasonboard.com>
 <20230119115503.268693-7-umang.jain@ideasonboard.com>
 <Y8nz1inld2Hwdc5i@pendragon.ideasonboard.com>
Content-Language: en-US
From:   Umang Jain <umang.jain@ideasonboard.com>
In-Reply-To: <Y8nz1inld2Hwdc5i@pendragon.ideasonboard.com>
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Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi Laurent,

On 1/20/23 7:22 AM, Laurent Pinchart wrote:
> Hi Umang,
>
> Thank you for the patch.
>
> On Thu, Jan 19, 2023 at 05:25:03PM +0530, Umang Jain wrote:
>> The devices that the vchiq interface registers(bcm2835-audio,
> Missing space before '('.
>
>> 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
> Drop one of the two "also".
>
>> 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.
> Greg, I don't know if you've followed the conversation in earlier mail
> threads, so I'll try to summarize it here.
>
> There are two layers involved: the VCHIQ layer, which has two clients
> (audio and MMAL), and the MMAL layer, which has multiple clients
> (camera, codec, ISP). The reason for this is that audio and mmal are
> separate hardware, while camera, codec and ISP share some hardware
> blocks.
>
> The VCHIQ layer provides a mailbox API to its clients to communicate
> with the firmware, and the MMAL layer provides another API implemented
> on top of the VCHIQ layer. Neither APIs offer a way to discover devices
> dynamically (that's not a feature implemented by the firmware). We've
> decided that implementing two buses would be overkill, so Umang went for
> a single vchiq_bus_type. The only value it provides is to stop abusing
> platform_device. That's pretty much it.
>
> Given the above explanation, do you still think the additional
> complexity introduced by the vchiq bus type is worth it (it more or less
> duplicates a small subset of the platform bus type implementation), and
> are you fine with a single bus type, even if it doesn't exactly match
> the firmware layers ?
>
>> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
>> ---
>>   .../vc04_services/bcm2835-audio/bcm2835.c     |  19 ++-
>>   .../bcm2835-camera/bcm2835-camera.c           |  17 ++-
>>   .../interface/vchiq_arm/vchiq_arm.c           | 121 +++++++++++++++---
>>   .../interface/vchiq_arm/vchiq_arm.h           |   1 +
>>   4 files changed, 117 insertions(+), 41 deletions(-)
>>
>> diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835.c
>> index 00bc898b0189..9f3af84f5d5d 100644
>> --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835.c
>> +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835.c
>> @@ -1,12 +1,11 @@
>>   // SPDX-License-Identifier: GPL-2.0
>>   /* Copyright 2011 Broadcom Corporation.  All rights reserved. */
>>   
>> -#include <linux/platform_device.h>
>> -
>>   #include <linux/init.h>
>>   #include <linux/slab.h>
>>   #include <linux/module.h>
>>   
>> +#include "../interface/vchiq_arm/vchiq_arm.h"
>>   #include "bcm2835.h"
>>   
>>   static bool enable_hdmi;
>> @@ -268,9 +267,8 @@ static int snd_add_child_devices(struct device *device, u32 numchans)
>>   	return 0;
>>   }
>>   
>> -static int snd_bcm2835_alsa_probe(struct platform_device *pdev)
>> +static int snd_bcm2835_alsa_probe(struct device *dev)
>>   {
>> -	struct device *dev = &pdev->dev;
>>   	int err;
>>   
>>   	if (num_channels <= 0 || num_channels > MAX_SUBSTREAMS) {
>> @@ -292,30 +290,29 @@ static int snd_bcm2835_alsa_probe(struct platform_device *pdev)
>>   
>>   #ifdef CONFIG_PM
>>   
>> -static int snd_bcm2835_alsa_suspend(struct platform_device *pdev,
>> +static int snd_bcm2835_alsa_suspend(struct device *pdev,
>>   				    pm_message_t state)
>>   {
>>   	return 0;
>>   }
>>   
>> -static int snd_bcm2835_alsa_resume(struct platform_device *pdev)
>> +static int snd_bcm2835_alsa_resume(struct device *pdev)
>>   {
>>   	return 0;
>>   }
>>   
>>   #endif
>>   
>> -static struct platform_driver bcm2835_alsa_driver = {
>> +static struct device_driver bcm2835_alsa_driver = {
>>   	.probe = snd_bcm2835_alsa_probe,
>>   #ifdef CONFIG_PM
>>   	.suspend = snd_bcm2835_alsa_suspend,
>>   	.resume = snd_bcm2835_alsa_resume,
>>   #endif
>> -	.driver = {
>> -		.name = "bcm2835_audio",
>> -	},
>> +	.name = "bcm2835_audio",
>> +	.bus = &vchiq_bus_type,
>>   };
>> -module_platform_driver(bcm2835_alsa_driver);
>> +module_driver(bcm2835_alsa_driver, driver_register, driver_unregister);
> Shouldn't you create a struct vchiq_device that wraps struct device, a
> struct vchiq_driver that wraps struct device_driver, and a
> module_vchiq_driver() macro ? It shouldn't be up to individual drivers
> to deal with the plumbing.
>
>>   
>>   MODULE_AUTHOR("Dom Cobley");
>>   MODULE_DESCRIPTION("Alsa driver for BCM2835 chip");
>> diff --git a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
>> index 4f81765912ea..199a49f9ec1e 100644
>> --- a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
>> +++ b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
>> @@ -24,8 +24,8 @@
>>   #include <media/v4l2-event.h>
>>   #include <media/v4l2-common.h>
>>   #include <linux/delay.h>
>> -#include <linux/platform_device.h>
>>   
>> +#include "../interface/vchiq_arm/vchiq_arm.h"
>>   #include "../vchiq-mmal/mmal-common.h"
>>   #include "../vchiq-mmal/mmal-encodings.h"
>>   #include "../vchiq-mmal/mmal-vchiq.h"
>> @@ -1841,7 +1841,7 @@ static struct v4l2_format default_v4l2_format = {
>>   	.fmt.pix.sizeimage = 1024 * 768,
>>   };
>>   
>> -static int bcm2835_mmal_probe(struct platform_device *pdev)
>> +static int bcm2835_mmal_probe(struct device *device)
>>   {
>>   	int ret;
>>   	struct bcm2835_mmal_dev *dev;
>> @@ -1896,7 +1896,7 @@ static int bcm2835_mmal_probe(struct platform_device *pdev)
>>   						       &camera_instance);
>>   		ret = v4l2_device_register(NULL, &dev->v4l2_dev);
>>   		if (ret) {
>> -			dev_err(&pdev->dev, "%s: could not register V4L2 device: %d\n",
>> +			dev_err(device, "%s: could not register V4L2 device: %d\n",
>>   				__func__, ret);
>>   			goto free_dev;
>>   		}
>> @@ -1976,7 +1976,7 @@ static int bcm2835_mmal_probe(struct platform_device *pdev)
>>   	return ret;
>>   }
>>   
>> -static int bcm2835_mmal_remove(struct platform_device *pdev)
>> +static int bcm2835_mmal_remove(struct device *device)
>>   {
>>   	int camera;
>>   	struct vchiq_mmal_instance *instance = gdev[0]->instance;
>> @@ -1990,15 +1990,14 @@ static int bcm2835_mmal_remove(struct platform_device *pdev)
>>   	return 0;
>>   }
>>   
>> -static struct platform_driver bcm2835_camera_driver = {
>> +static struct device_driver bcm2835_camera_driver = {
>> +	.name		= "bcm2835-camera",
>>   	.probe		= bcm2835_mmal_probe,
>>   	.remove		= bcm2835_mmal_remove,
>> -	.driver		= {
>> -		.name	= "bcm2835-camera",
>> -	},
>> +	.bus		= &vchiq_bus_type,
>>   };
>>   
>> -module_platform_driver(bcm2835_camera_driver)
>> +module_driver(bcm2835_camera_driver, driver_register, driver_unregister)
>>   
>>   MODULE_DESCRIPTION("Broadcom 2835 MMAL video capture");
>>   MODULE_AUTHOR("Vincent Sanders");
>> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
>> index 22de23f3af02..86c8e5df7cf6 100644
>> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
>> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
>> @@ -12,6 +12,8 @@
>>   #include <linux/cdev.h>
>>   #include <linux/fs.h>
>>   #include <linux/device.h>
>> +#include <linux/device/bus.h>
>> +#include <linux/string.h>
>>   #include <linux/mm.h>
>>   #include <linux/highmem.h>
>>   #include <linux/pagemap.h>
>> @@ -65,9 +67,6 @@ int vchiq_susp_log_level = VCHIQ_LOG_ERROR;
>>   DEFINE_SPINLOCK(msg_queue_spinlock);
>>   struct vchiq_state g_state;
>>   
>> -static struct platform_device *bcm2835_camera;
>> -static struct platform_device *bcm2835_audio;
>> -
>>   struct vchiq_drvdata {
>>   	const unsigned int cache_line_size;
>>   	struct rpi_firmware *fw;
>> @@ -132,6 +131,51 @@ struct vchiq_pagelist_info {
>>   	unsigned int scatterlist_mapped;
>>   };
>>   
>> +struct vchiq_device {
>> +	const char *name;
>> +	struct device dev;
>> +};
> Ah there we go :-) Move this structure to a header file that drivers can
> include. I'd name it vchiq_device.h. The code below should go to
> vchiq_device.c.
>
> I would also move the dev field first.
>
>> +
>> +static ssize_t vchiq_dev_show(struct device *dev,
>> +			      struct device_attribute *attr, char *buf)
>> +{
>> +	struct vchiq_device *device = container_of(dev, struct vchiq_device, dev);
>> +
>> +	return sprintf(buf, "%s", device->name);
>> +}
>> +
>> +static DEVICE_ATTR_RO(vchiq_dev);
>> +
>> +static struct attribute *vchiq_dev_attrs[] = {
>> +	&dev_attr_vchiq_dev.attr,
>> +	NULL
>> +};
>> +
>> +ATTRIBUTE_GROUPS(vchiq_dev);
>> +
>> +static const struct device_type vchiq_device_type = {
>> +	.groups         = vchiq_dev_groups
>> +};
>> +
>> +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;
>> +}
>> +
>> +struct bus_type vchiq_bus_type = {
>> +	.name   = "vchiq-bus",
>> +	.match  = vchiq_bus_type_match,
>> +};
>> +EXPORT_SYMBOL(vchiq_bus_type);
> EXPORT_SYMBOL_GPL ?
>
>> +
>> +static const char *const vchiq_devices[] = {
>> +	"bcm2835_audio",
>> +	"bcm2835-camera",
>> +};
> This however should stay in this file.
>
>> +
>>   static void __iomem *g_regs;
>>   /* This value is the size of the L2 cache lines as understood by the
>>    * VPU firmware, which determines the required alignment of the
>> @@ -1763,26 +1807,52 @@ static const struct of_device_id vchiq_of_match[] = {
>>   };
>>   MODULE_DEVICE_TABLE(of, vchiq_of_match);
>>   
>> -static struct platform_device *
>> +static void
>> +vchiq_release_device(struct device *dev)
>> +{
>> +	struct vchiq_device *device;
>> +
>> +	device = container_of(dev, struct vchiq_device, dev);
>> +	kfree(device);
>> +}
>> +
>> +static int
>>   vchiq_register_child(struct platform_device *pdev, const char *name)
> Pass a struct device * for the first argument, you don't need a platform
> device. I'd also name the function vchiq_register_device, and rename the
> pdev parameter to parent.
>
>>   {
>> -	struct platform_device_info pdevinfo;
>> -	struct platform_device *child;
>> +	struct vchiq_device *device = NULL;
>> +	int ret;
>>   
>> -	memset(&pdevinfo, 0, sizeof(pdevinfo));
>> +	device = kzalloc(sizeof(*device), GFP_KERNEL);
>> +	if (!device)
>> +		return -ENOMEM;
>>   
>> -	pdevinfo.parent = &pdev->dev;
>> -	pdevinfo.name = name;
>> -	pdevinfo.id = PLATFORM_DEVID_NONE;
>> -	pdevinfo.dma_mask = DMA_BIT_MASK(32);
>> +	device->name = name;
>> +	device->dev.init_name = name;
>> +	device->dev.parent = &pdev->dev;
>> +	device->dev.bus = &vchiq_bus_type;
>> +	device->dev.type = &vchiq_device_type;
>> +	device->dev.release = vchiq_release_device;
>> +
>> +	ret = dma_set_mask_and_coherent(&device->dev, DMA_BIT_MASK(32));
> Do vchiq devices perform DMA ?

As far as I can tell, the devices right now (in the mainline) don't use 
DMA allocation. So it's not relevant right now.

But looking at RPi's BSP - the vc-sm-cma driver does the DMA. So 
probably we want to dma_set_mask_and_coherent() for that only?

>
>> +	if (ret < 0) {
>> +		vchiq_release_device(&device->dev);
>> +		return ret;
>> +	}
>>   
>> -	child = platform_device_register_full(&pdevinfo);
>> -	if (IS_ERR(child)) {
>> -		dev_warn(&pdev->dev, "%s not registered\n", name);
>> -		child = NULL;
>> +	ret = device_register(&device->dev);
>> +	if (ret) {
>> +		put_device(&device->dev);
>> +		return -EINVAL;
>>   	}
>>   
>> -	return child;
>> +	return 0;
>> +}
>> +
>> +static int
>> +vchiq_unregister_child(struct device *dev, void *data)
>> +{
>> +	device_unregister(dev);
>> +	return 0;
>>   }
>>   
>>   static int vchiq_probe(struct platform_device *pdev)
>> @@ -1790,7 +1860,7 @@ static int vchiq_probe(struct platform_device *pdev)
>>   	struct device_node *fw_node;
>>   	const struct of_device_id *of_id;
>>   	struct vchiq_drvdata *drvdata;
>> -	int err;
>> +	int i, err;
> i can be an unsigned int.
>
>>   
>>   	of_id = of_match_node(vchiq_of_match, pdev->dev.of_node);
>>   	drvdata = (struct vchiq_drvdata *)of_id->data;
>> @@ -1832,8 +1902,12 @@ static int vchiq_probe(struct platform_device *pdev)
>>   		goto error_exit;
>>   	}
>>   
>> -	bcm2835_camera = vchiq_register_child(pdev, "bcm2835-camera");
>> -	bcm2835_audio = vchiq_register_child(pdev, "bcm2835_audio");
>> +	for (i = 0; i < ARRAY_SIZE(vchiq_devices); i++) {
>> +		err = vchiq_register_child(pdev, vchiq_devices[i]);
>> +		if (!err)
>> +			dev_err(&pdev->dev, "Failed to register %s vchiq device\n",
>> +				vchiq_devices[i]);
>> +	}
>>   
>>   	return 0;
>>   
>> @@ -1845,8 +1919,8 @@ static int vchiq_probe(struct platform_device *pdev)
>>   
>>   static int vchiq_remove(struct platform_device *pdev)
>>   {
>> -	platform_device_unregister(bcm2835_audio);
>> -	platform_device_unregister(bcm2835_camera);
>> +	bus_for_each_dev(&vchiq_bus_type, NULL, NULL, vchiq_unregister_child);
>> +
>>   	vchiq_debugfs_deinit();
>>   	vchiq_deregister_chrdev();
>>   
>> @@ -1866,6 +1940,10 @@ static int __init vchiq_driver_init(void)
>>   {
>>   	int ret;
>>   
>> +	ret = bus_register(&vchiq_bus_type);
>> +	if (ret)
>> +		pr_err("Failed to register %s\n", vchiq_bus_type.name);
> This should be a fatal error, you should return an error value.
>
>> +
>>   	ret = platform_driver_register(&vchiq_driver);
>>   	if (ret)
>>   		pr_err("Failed to register vchiq driver\n");
>> @@ -1876,6 +1954,7 @@ module_init(vchiq_driver_init);
>>   
>>   static void __exit vchiq_driver_exit(void)
>>   {
>> +	bus_unregister(&vchiq_bus_type);
>>   	platform_driver_unregister(&vchiq_driver);
>>   }
>>   module_exit(vchiq_driver_exit);
>> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
>> index 2fb31f9b527f..98c3af32774a 100644
>> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
>> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
>> @@ -81,6 +81,7 @@ extern int vchiq_susp_log_level;
>>   
>>   extern spinlock_t msg_queue_spinlock;
>>   extern struct vchiq_state g_state;
>> +extern struct bus_type vchiq_bus_type;
>>   
>>   extern struct vchiq_state *
>>   vchiq_get_state(void);