Re: [PATCH] drm/bridge: Avoid uninitialized variable warning

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue, 28 Jun 2022 09:59:51 +0300
Dan Carpenter <dan.carpenter@oracle.com> wrote:

> This works, but technically it uses "num_in_bus_fmts" before it has been
> initialized so it leads to static checker warnings and probably KMEMsan
> warnings at run time.  Reverse the checks so it checks for failure first
> and then check for unsupported formats next.
> 
> Fixes: f32df58acc68 ("drm/bridge: Add the necessary bits to support bus format negotiation")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>  drivers/gpu/drm/drm_bridge.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index e275b4ca344b..00cbde654472 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -897,10 +897,10 @@ static int select_bus_fmt_recursive(struct drm_bridge *first_bridge,
>  							conn_state,
>  							out_bus_fmt,
>  							&num_in_bus_fmts);
> -	if (!num_in_bus_fmts)
> -		return -ENOTSUPP;
> -	else if (!in_bus_fmts)
> +	if (!in_bus_fmts)
>  		return -ENOMEM;
> +	else if (!num_in_bus_fmts)
> +		return -ENOTSUPP;

Well, it changes the error we return when num_in_bus_fmts = 0
&& in_bus_fmts == NULL which is not an ENOMEM situation, so I'd rather
initialize num_{in,out}_bus_fmts to 0 here.

>  
>  	if (first_bridge == cur_bridge) {
>  		cur_state->input_bus_cfg.format = in_bus_fmts[0];
> @@ -993,10 +993,10 @@ drm_atomic_bridge_chain_select_bus_fmts(struct drm_bridge *bridge,
>  							crtc_state,
>  							conn_state,
>  							&num_out_bus_fmts);
> -		if (!num_out_bus_fmts)
> -			return -ENOTSUPP;
> -		else if (!out_bus_fmts)
> +		if (!out_bus_fmts)
>  			return -ENOMEM;
> +		else if (!num_out_bus_fmts)
> +			return -ENOTSUPP;
>  	} else {
>  		num_out_bus_fmts = 1;
>  		out_bus_fmts = kmalloc(sizeof(*out_bus_fmts), GFP_KERNEL);