linux-kernel - Re: [PATCH] drm: Grab reference of connector before return connector from sun4i_tcon_get

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Message-ID: <87cznkdo6p.fsf@intel.com>
Date:   Mon, 01 Nov 2021 15:02:06 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     He Ying <heying24@...wei.com>, mripard@...nel.org, wens@...e.org,
        airlied@...ux.ie, daniel@...ll.ch, jernej.skrabec@...il.com
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH] drm: Grab reference of connector before return connector from sun4i_tcon_get_connector

On Mon, 01 Nov 2021, He Ying <heying24@...wei.com> wrote:
> From the comments of drm_for_each_connector_iter(), we know
> that "connector is only valid within the list body, if you
> want to use connector after calling drm_connector_list_iter_end()
> then you need to grab your own reference first using
> drm_connector_get()". So fix the wrong use of connector
> according to the comments and then call drm_connector_put()
> after using connector finishes.
>
> Signed-off-by: He Ying <heying24@...wei.com>

Please use "drm/sun4i:" subject prefix for sun4i patches.

BR,
Jani.


> ---
>  drivers/gpu/drm/sun4i/sun4i_tcon.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> index 9f06dec0fc61..24fa6784ee5f 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> @@ -47,12 +47,12 @@ static struct drm_connector *sun4i_tcon_get_connector(const struct drm_encoder *
>  	drm_connector_list_iter_begin(encoder->dev, &iter);
>  	drm_for_each_connector_iter(connector, &iter)
>  		if (connector->encoder == encoder) {
> -			drm_connector_list_iter_end(&iter);
> -			return connector;
> +			drm_connector_get(connector);
> +			break;
>  		}
>  	drm_connector_list_iter_end(&iter);
>  
> -	return NULL;
> +	return connector;
>  }
>  
>  static int sun4i_tcon_get_pixel_depth(const struct drm_encoder *encoder)
> @@ -65,6 +65,7 @@ static int sun4i_tcon_get_pixel_depth(const struct drm_encoder *encoder)
>  		return -EINVAL;
>  
>  	info = &connector->display_info;
> +	drm_connector_put(connector);
>  	if (info->num_bus_formats != 1)
>  		return -EINVAL;
>  
> @@ -361,6 +362,7 @@ static void sun4i_tcon0_mode_set_cpu(struct sun4i_tcon *tcon,
>  	/* TODO support normal CPU interface modes */
>  	struct sun6i_dsi *dsi = encoder_to_sun6i_dsi(encoder);
>  	struct mipi_dsi_device *device = dsi->device;
> +	struct drm_connector *connector;
>  	u8 bpp = mipi_dsi_pixel_format_to_bpp(device->format);
>  	u8 lanes = device->lanes;
>  	u32 block_space, start_delay;
> @@ -372,7 +374,9 @@ static void sun4i_tcon0_mode_set_cpu(struct sun4i_tcon *tcon,
>  	sun4i_tcon0_mode_set_common(tcon, mode);
>  
>  	/* Set dithering if needed */
> -	sun4i_tcon0_mode_set_dithering(tcon, sun4i_tcon_get_connector(encoder));
> +	connector = sun4i_tcon_get_connector(encoder);
> +	sun4i_tcon0_mode_set_dithering(tcon, connector);
> +	drm_connector_put(connector);
>  
>  	regmap_update_bits(tcon->regs, SUN4I_TCON0_CTL_REG,
>  			   SUN4I_TCON0_CTL_IF_MASK,
> @@ -430,6 +434,7 @@ static void sun4i_tcon0_mode_set_lvds(struct sun4i_tcon *tcon,
>  				      const struct drm_display_mode *mode)
>  {
>  	unsigned int bp;
> +	struct drm_connector *connector;
>  	u8 clk_delay;
>  	u32 reg, val = 0;
>  
> @@ -440,7 +445,9 @@ static void sun4i_tcon0_mode_set_lvds(struct sun4i_tcon *tcon,
>  	sun4i_tcon0_mode_set_common(tcon, mode);
>  
>  	/* Set dithering if needed */
> -	sun4i_tcon0_mode_set_dithering(tcon, sun4i_tcon_get_connector(encoder));
> +	connector = sun4i_tcon_get_connector(encoder);
> +	sun4i_tcon0_mode_set_dithering(tcon, connector);
> +	drm_connector_put(connector);
>  
>  	/* Adjust clock delay */
>  	clk_delay = sun4i_tcon_get_clk_delay(mode, 0);
> @@ -518,6 +525,7 @@ static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
>  
>  	/* Set dithering if needed */
>  	sun4i_tcon0_mode_set_dithering(tcon, connector);
> +	drm_connector_put(connector);
>  
>  	/* Adjust clock delay */
>  	clk_delay = sun4i_tcon_get_clk_delay(mode, 0);

-- 
Jani Nikula, Intel Open Source Graphics Center