linux-kernel - Re: [PATCH v2 01/18] media: allegro: nal-hevc: Refactor nal_hevc_sub_layer_hrd

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Date: Wed, 8 May 2024 10:53:27 +0200
From: Michael Tretter <m.tretter@...gutronix.de>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Pengutronix Kernel Team <kernel@...gutronix.de>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Michal Simek <michal.simek@....com>,
	Andy Walls <awalls@...metrocast.net>,
	Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
	Vikash Garodia <quic_vgarodia@...cinc.com>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
	Hans Verkuil <hverkuil-cisco@...all.nl>
Subject: Re: [PATCH v2 01/18] media: allegro: nal-hevc: Refactor
 nal_hevc_sub_layer_hrd_parameters

On Tue, 07 May 2024 16:27:06 +0000, Ricardo Ribalda wrote:
> Replace all the single elements arrays with the element itself.
> 
> Pahole shows the same padding and alignment for x86 and arm in both
> situations.
> 
> This fixes this cocci warning:
> drivers/media/platform/allegro-dvt/nal-hevc.h:102:14-22: WARNING use flexible-array member instead (https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays)

Thanks for the patch.

> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/platform/allegro-dvt/allegro-core.c |  6 +++---
>  drivers/media/platform/allegro-dvt/nal-hevc.c     | 11 +++--------
>  drivers/media/platform/allegro-dvt/nal-hevc.h     |  6 +++---
>  3 files changed, 9 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/media/platform/allegro-dvt/allegro-core.c b/drivers/media/platform/allegro-dvt/allegro-core.c
> index da61f9beb6b4..369bd88cc0ae 100644
> --- a/drivers/media/platform/allegro-dvt/allegro-core.c
> +++ b/drivers/media/platform/allegro-dvt/allegro-core.c
> @@ -1852,14 +1852,14 @@ static ssize_t allegro_hevc_write_sps(struct allegro_channel *channel,
>  	hrd->dpb_output_delay_length_minus1 = 30;
>  
>  	hrd->bit_rate_scale = ffs(channel->bitrate_peak) - 6;
> -	hrd->vcl_hrd[0].bit_rate_value_minus1[0] =
> +	hrd->vcl_hrd[0].bit_rate_value_minus1 =
>  		(channel->bitrate_peak >> (6 + hrd->bit_rate_scale)) - 1;
>  
>  	cpb_size = v4l2_ctrl_g_ctrl(channel->mpeg_video_cpb_size) * 1000;
>  	hrd->cpb_size_scale = ffs(cpb_size) - 4;
> -	hrd->vcl_hrd[0].cpb_size_value_minus1[0] = (cpb_size >> (4 + hrd->cpb_size_scale)) - 1;
> +	hrd->vcl_hrd[0].cpb_size_value_minus1 = (cpb_size >> (4 + hrd->cpb_size_scale)) - 1;
>  
> -	hrd->vcl_hrd[0].cbr_flag[0] = !v4l2_ctrl_g_ctrl(channel->mpeg_video_frame_rc_enable);
> +	hrd->vcl_hrd[0].cbr_flag = !v4l2_ctrl_g_ctrl(channel->mpeg_video_frame_rc_enable);
>  
>  	size = nal_hevc_write_sps(&dev->plat_dev->dev, dest, n, sps);
>  
> diff --git a/drivers/media/platform/allegro-dvt/nal-hevc.c b/drivers/media/platform/allegro-dvt/nal-hevc.c
> index 9cdf2756e0a3..575089522df5 100644
> --- a/drivers/media/platform/allegro-dvt/nal-hevc.c
> +++ b/drivers/media/platform/allegro-dvt/nal-hevc.c
> @@ -210,14 +210,9 @@ static void nal_hevc_rbsp_vps(struct rbsp *rbsp, struct nal_hevc_vps *vps)
>  static void nal_hevc_rbsp_sub_layer_hrd_parameters(struct rbsp *rbsp,
>  						   struct nal_hevc_sub_layer_hrd_parameters *hrd)
>  {
> -	unsigned int i;
> -	unsigned int cpb_cnt = 1;
> -
> -	for (i = 0; i < cpb_cnt; i++) {
> -		rbsp_uev(rbsp, &hrd->bit_rate_value_minus1[i]);
> -		rbsp_uev(rbsp, &hrd->cpb_size_value_minus1[i]);
> -		rbsp_bit(rbsp, &hrd->cbr_flag[i]);
> -	}
> +	rbsp_uev(rbsp, &hrd->bit_rate_value_minus1);
> +	rbsp_uev(rbsp, &hrd->cpb_size_value_minus1);
> +	rbsp_bit(rbsp, &hrd->cbr_flag);
>  }
>  
>  static void nal_hevc_rbsp_hrd_parameters(struct rbsp *rbsp,
> diff --git a/drivers/media/platform/allegro-dvt/nal-hevc.h b/drivers/media/platform/allegro-dvt/nal-hevc.h
> index eb46f12aae80..afa7a9d7d654 100644
> --- a/drivers/media/platform/allegro-dvt/nal-hevc.h
> +++ b/drivers/media/platform/allegro-dvt/nal-hevc.h
> @@ -97,9 +97,9 @@ struct nal_hevc_vps {
>  };
>  
>  struct nal_hevc_sub_layer_hrd_parameters {
> -	unsigned int bit_rate_value_minus1[1];
> -	unsigned int cpb_size_value_minus1[1];
> -	unsigned int cbr_flag[1];
> +	unsigned int bit_rate_value_minus1;
> +	unsigned int cpb_size_value_minus1;
> +	unsigned int cbr_flag;

The struct is modeled after the specification in ITU-T H.265, which
defines the fields as arrays. It's a limitation of the current
implementation that only a single element is supported.

Maybe replacing the hard coded values with a constant would be more
appropriate to document this limitation.

Michael

>  };
>  
>  struct nal_hevc_hrd_parameters {
> 
> -- 
> 2.45.0.rc1.225.g2a3ae87e7f-goog
> 
>