linux-kernel - Re: [PATCH] staging: vc04_services: vchiq_arm: Create platform

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Date:   Wed, 21 Dec 2022 13:14:59 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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>
Subject: Re: [PATCH] staging: vc04_services: vchiq_arm: Create
 platform_device per device

Hi Umang,

Thank you for the patch.

On Tue, Dec 20, 2022 at 02:14:04PM +0530, Umang Jain wrote:
> Create a proper per device platorm_device structure for all the child
> devices that needs to be registered by vchiq platform driver. Replace
> the vchiq_register_child() with platform_add_devices() to register the
> child devices.

This explains what the patch does, but not why.

> This is part of an effort to address TODO item "Get rid of all non
> essential global structures and create a proper per device structure"

And this explains part of the reason only. Could you please expand the
commit message with the reasoning behind this change ? It's not clear
from the change below why this is needed and good.

> Signed-off-by: Umang Jain <umang.jain@...asonboard.com>
> ---
>  .../interface/vchiq_arm/vchiq_arm.c           | 59 ++++++++++---------
>  1 file changed, 31 insertions(+), 28 deletions(-)
> 
> 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..fa42ea3791a7 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> @@ -65,8 +65,29 @@ 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;
> +static u64 vchiq_device_dmamask = DMA_BIT_MASK(32);

The fact that this isn't const and is used by two different
platform_device instances is worrying. Either it can be made const, or
it's wrong.

> +
> +static struct platform_device bcm2835_camera = {
> +	.name		= "bcm2835-camera",
> +	.id		= PLATFORM_DEVID_NONE,
> +	.dev		= {
> +		.dma_mask	= &vchiq_device_dmamask,
> +	}
> +};
> +
> +static struct platform_device bcm2835_audio = {
> +	.name		= "bcm2835_audio",
> +	.id		= PLATFORM_DEVID_NONE,
> +	.dev		= {
> +		.dma_mask	= &vchiq_device_dmamask,
> +	}
> +

Extra blank line.

> +};
> +
> +static struct platform_device *vchiq_devices[] __initdata = {

Make it const.

> +	&bcm2835_camera,
> +	&bcm2835_audio,
> +};
>  
>  struct vchiq_drvdata {
>  	const unsigned int cache_line_size;
> @@ -1763,28 +1784,6 @@ static const struct of_device_id vchiq_of_match[] = {
>  };
>  MODULE_DEVICE_TABLE(of, vchiq_of_match);
>  
> -static struct platform_device *
> -vchiq_register_child(struct platform_device *pdev, const char *name)
> -{
> -	struct platform_device_info pdevinfo;
> -	struct platform_device *child;
> -
> -	memset(&pdevinfo, 0, sizeof(pdevinfo));
> -
> -	pdevinfo.parent = &pdev->dev;
> -	pdevinfo.name = name;
> -	pdevinfo.id = PLATFORM_DEVID_NONE;
> -	pdevinfo.dma_mask = DMA_BIT_MASK(32);
> -
> -	child = platform_device_register_full(&pdevinfo);
> -	if (IS_ERR(child)) {
> -		dev_warn(&pdev->dev, "%s not registered\n", name);
> -		child = NULL;
> -	}
> -
> -	return child;
> -}
> -
>  static int vchiq_probe(struct platform_device *pdev)
>  {
>  	struct device_node *fw_node;
> @@ -1832,8 +1831,11 @@ 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");
> +	err = platform_add_devices(vchiq_devices, ARRAY_SIZE(vchiq_devices));
> +	if (err) {
> +		dev_warn(&pdev->dev, "Failed to add vchiq child devices");
> +		goto error_exit;
> +	}

If you unbind and rebind this driver, the platform_device instances
defined as global variables will be reused, and I'm pretty sure that
will cause issues, for instance with the kobj->state_initialized check
in kobject_init() (called from device_initialize(), itself called from
platform_device_register(), from platform_add_devices()). I'm not sure
static instances of platform_device are a very good idea in general.

>  
>  	return 0;
>  
> @@ -1845,8 +1847,9 @@ 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);
> +	for (unsigned int i = 0; i < ARRAY_SIZE(vchiq_devices); i++)
> +		platform_device_unregister(vchiq_devices[i]);
> +
>  	vchiq_debugfs_deinit();
>  	vchiq_deregister_chrdev();
>  

-- 
Regards,

Laurent Pinchart