linux-kernel - Re: [PATCH 1/1] drm/bridge: anx78xx: fix integer type used for storing dp link rate

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Date:   Fri, 17 Jan 2020 11:03:03 +0100
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Tobias Schramm <t.schramm@...jaro.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] drm/bridge: anx78xx: fix integer type used for
 storing dp link rate

On 09.01.2020 09:48, Tobias Schramm wrote:
> commit ff1e8fb68ea0 ("drm/bridge: analogix-anx78xx: Avoid drm_dp_link helpers")
> changed the link training logic to remove use of drm_dp_link helpers. However
> the new logic stores the maximum link rate in a u8, overflowing it.
> This commit changes the logic to store the max link rate in a unsigned int
> instead.
>
> Signed-off-by: Tobias Schramm <t.schramm@...jaro.org>
> ---
>  drivers/gpu/drm/bridge/analogix-anx78xx.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/analogix-anx78xx.c b/drivers/gpu/drm/bridge/analogix-anx78xx.c
> index 274989f96a91..0f38b8c40dff 100644
> --- a/drivers/gpu/drm/bridge/analogix-anx78xx.c
> +++ b/drivers/gpu/drm/bridge/analogix-anx78xx.c
> @@ -748,6 +748,7 @@ static int anx78xx_init_pdata(struct anx78xx *anx78xx)
>  static int anx78xx_dp_link_training(struct anx78xx *anx78xx)
>  {
>  	u8 dp_bw, dpcd[2];
> +	unsigned int max_link_rate;
>  	int err;
>  
>  	err = regmap_write(anx78xx->map[I2C_IDX_RX_P0], SP_HDMI_MUTE_CTRL_REG,
> @@ -866,8 +867,8 @@ static int anx78xx_dp_link_training(struct anx78xx *anx78xx)
>  	if (err)
>  		return err;
>  
> -	dpcd[0] = drm_dp_max_link_rate(anx78xx->dpcd);
> -	dpcd[0] = drm_dp_link_rate_to_bw_code(dpcd[0]);
> +	max_link_rate = drm_dp_max_link_rate(anx78xx->dpcd);
> +	dpcd[0] = drm_dp_link_rate_to_bw_code(max_link_rate);


The code converts bw_code to rate, then reverse, maybe it should be
simplified:

dpcd[0] = anx78xx->dpcd[DP_MAX_LINK_RATE];


Regards

Andrzej


>  	err = regmap_write(anx78xx->map[I2C_IDX_TX_P0],
>  			   SP_DP_MAIN_LINK_BW_SET_REG, dpcd[0]);
>  	if (err)