linux-kernel - Re: [PATCH v2] drm/hisilicon: Code refactoring for hibmc_drv

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Message-ID: <21d9f165-3fe9-d0cb-35ce-c91889e7e0dd@suse.de>
Date:   Thu, 18 Jun 2020 15:52:29 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Tian Tao <tiantao6@...ilicon.com>, puck.chen@...ilicon.com,
        airlied@...ux.ie, daniel@...ll.ch, kraxel@...hat.com,
        alexander.deucher@....com, tglx@...utronix.de,
        dri-devel@...ts.freedesktop.org, xinliang.liu@...aro.org,
        linux-kernel@...r.kernel.org
Cc:     linuxarm@...wei.com
Subject: Re: [PATCH v2] drm/hisilicon: Code refactoring for hibmc_drv_vdac

Hi,

sorry for letting these patches sit around for so long. I'd say that if
you waited for a week or two without further responses, it's ok to ping
people.

Am 11.04.20 um 08:25 schrieb Tian Tao:
> code refactoring for hibmc_drv_vdac.c, no actual function changes.
> 
> v2:
> remove the debug message.
> 
> Signed-off-by: Tian Tao <tiantao6@...ilicon.com>
> Reviewed-by: Joe Perches <joe@...ches.com>
> ---
>  drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_vdac.c | 50 +++++++-----------------
>  1 file changed, 14 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_vdac.c b/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_vdac.c
> index 678ac2e..077b7996 100644
> --- a/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_vdac.c
> +++ b/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_vdac.c
> @@ -52,32 +52,6 @@ static const struct drm_connector_funcs hibmc_connector_funcs = {
>  	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
>  };
>  
> -static struct drm_connector *
> -hibmc_connector_init(struct hibmc_drm_private *priv)
> -{
> -	struct drm_device *dev = priv->dev;
> -	struct drm_connector *connector;
> -	int ret;
> -
> -	connector = devm_kzalloc(dev->dev, sizeof(*connector), GFP_KERNEL);
> -	if (!connector) {
> -		DRM_ERROR("failed to alloc memory when init connector\n");
> -		return ERR_PTR(-ENOMEM);
> -	}
> -
> -	ret = drm_connector_init(dev, connector,
> -				 &hibmc_connector_funcs,
> -				 DRM_MODE_CONNECTOR_VGA);
> -	if (ret) {
> -		DRM_ERROR("failed to init connector: %d\n", ret);
> -		return ERR_PTR(ret);
> -	}
> -	drm_connector_helper_add(connector,
> -				 &hibmc_connector_helper_funcs);
> -
> -	return connector;
> -}
> -
>  static void hibmc_encoder_mode_set(struct drm_encoder *encoder,
>  				   struct drm_display_mode *mode,
>  				   struct drm_display_mode *adj_mode)
> @@ -109,18 +83,9 @@ int hibmc_vdac_init(struct hibmc_drm_private *priv)
>  	struct drm_connector *connector;
>  	int ret;
>  
> -	connector = hibmc_connector_init(priv);
> -	if (IS_ERR(connector)) {
> -		DRM_ERROR("failed to create connector: %ld\n",
> -			  PTR_ERR(connector));
> -		return PTR_ERR(connector);
> -	}
> -
>  	encoder = devm_kzalloc(dev->dev, sizeof(*encoder), GFP_KERNEL);
> -	if (!encoder) {
> -		DRM_ERROR("failed to alloc memory when init encoder\n");
> +	if (!encoder)
>  		return -ENOMEM;
> -	}
>  
>  	encoder->possible_crtcs = 0x1;
>  	ret = drm_encoder_init(dev, encoder, &hibmc_encoder_funcs,
> @@ -131,6 +96,19 @@ int hibmc_vdac_init(struct hibmc_drm_private *priv)
>  	}
>  
>  	drm_encoder_helper_add(encoder, &hibmc_encoder_helper_funcs);
> +
> +	connector = devm_kzalloc(dev->dev, sizeof(*connector), GFP_KERNEL);

Overall, the patch seems correct, expect for this line. DRM data
structures should now be allocated with drmm_kzalloc() in drm_managed.h.
It was added recently.

With devm_kzalloc(), the memory will be released when the HW device goes
away. If userspace still holds a reference, the driver can segfault.
Using drmm_kzalloc() delays the release until the memory is really unused.

However, hibmc's modesetting pipeline appears to be always the same. I
think you should consider embedding connector and encoder (and crtc) in
struct hibmc_drm_private. Would make the code simpler and more robust.

Best regards
Thomas



> +	if (!connector)
> +		return -ENOMEM;
> +
> +	ret = drm_connector_init(dev, connector, &hibmc_connector_funcs,
> +				 DRM_MODE_CONNECTOR_VGA);
> +	if (ret) {
> +		DRM_ERROR("failed to init connector: %d\n", ret);
> +		return ret;
> +	}
> +	drm_connector_helper_add(connector, &hibmc_connector_helper_funcs);
> +
>  	drm_connector_attach_encoder(connector, encoder);
>  
>  	return 0;
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer



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