linux-kernel - Re: [PATCH v2 1/3] drm/loongson: Add a helper for creating child devices

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Date: Sun, 26 May 2024 23:47:29 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	Markus Elfring <Markus.Elfring@....de>
Subject: Re: [PATCH v2 1/3] drm/loongson: Add a helper for creating child
 devices

On Mon, May 27, 2024 at 03:58:24AM +0800, Sui Jingfeng wrote:
> In some display subsystems, the functionality of a PCIe device may too
> complex to be managed by a single driver. A split of the functionality
> into child devices can helpful to achieve better modularity.
> 
> Another benefit is that we could migrate the dependency on exterinal
> modules to a submodule level with the helper created. For example, it's
> not uncommon that some exterinal module will return -EPROBE_DEFER to our
> driver during probe time. KMS driver has to tear down everything when it
> receives -EPROBE_DEFER, the problem is that it's completely not necessary
> and rising cyclic dependency problems if not process correctly.
> 
> Add the loongson_create_platform_device() function, which allows the KMS
> driver to create sub-devices for it. The manually created decice acts as
> agents for the principal part, migrate the potential issue to submodule.
> 
> Signed-off-by: Sui Jingfeng <sui.jingfeng@...ux.dev>
> ---
>  drivers/gpu/drm/loongson/loongson_device.c | 42 ++++++++++++++++++++++
>  drivers/gpu/drm/loongson/lsdc_drv.h        |  6 ++++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/drivers/gpu/drm/loongson/loongson_device.c b/drivers/gpu/drm/loongson/loongson_device.c
> index 9986c8a2a255..b268549d643e 100644
> --- a/drivers/gpu/drm/loongson/loongson_device.c
> +++ b/drivers/gpu/drm/loongson/loongson_device.c
> @@ -4,6 +4,7 @@
>   */
>  
>  #include <linux/pci.h>
> +#include <linux/platform_device.h>
>  
>  #include "lsdc_drv.h"
>  
> @@ -100,3 +101,44 @@ lsdc_device_probe(struct pci_dev *pdev, enum loongson_chip_id chip_id)
>  {
>  	return __chip_id_desc_table[chip_id];
>  }
> +
> +int loongson_create_platform_device(struct device *parent,
> +				    const char *name, int id,
> +				    struct resource *pres,
> +				    void *data,
> +				    struct platform_device **ppdev)
> +{
> +	struct platform_device *pdev;
> +	int ret;
> +
> +	pdev = platform_device_alloc(name, id);
> +	if (!pdev)
> +		return -ENOMEM;
> +
> +	pdev->dev.parent = parent;
> +
> +	if (pres) {
> +		ret = platform_device_add_resources(pdev, pres, 1);
> +		if (ret) {
> +			platform_device_put(pdev);
> +			return ret;
> +		}
> +	}
> +
> +	if (data) {
> +		void *pdata = kmalloc(sizeof(void *), GFP_KERNEL);
> +
> +		*(void **)pdata = data;
> +		pdev->dev.platform_data = pdata;
> +	}
> +
> +	ret = platform_device_add(pdev);
> +	if (ret) {
> +		platform_device_put(pdev);
> +		return ret;
> +	}

Please use platform_device_register_resndata().

> +
> +	*ppdev = pdev;
> +
> +	return 0;
> +}
> diff --git a/drivers/gpu/drm/loongson/lsdc_drv.h b/drivers/gpu/drm/loongson/lsdc_drv.h
> index fbf2d760ef27..a2c6b496a69f 100644
> --- a/drivers/gpu/drm/loongson/lsdc_drv.h
> +++ b/drivers/gpu/drm/loongson/lsdc_drv.h
> @@ -47,6 +47,12 @@ enum loongson_chip_id {
>  const struct lsdc_desc *
>  lsdc_device_probe(struct pci_dev *pdev, enum loongson_chip_id chip);
>  
> +int loongson_create_platform_device(struct device *parent,
> +				    const char *name, int id,
> +				    struct resource *pres,
> +				    void *data,
> +				    struct platform_device **ppdev);
> +
>  struct lsdc_kms_funcs;
>  
>  /* DC specific */
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry