linux-kernel - Re: [PATCH v2 4/4] media: aspeed: Fix timing polarity incorrect

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Message-ID: <418fc1b2-ddbe-24e3-82cc-aa8ce74f4507@xs4all.nl>
Date:   Fri, 21 Jan 2022 08:30:17 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Jammy Huang <jammy_huang@...eedtech.com>, eajames@...ux.ibm.com,
        mchehab@...nel.org, joel@....id.au, andrew@...id.au,
        linux-media@...r.kernel.org, openbmc@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] media: aspeed: Fix timing polarity incorrect

On 12/22/21 09:21, Jammy Huang wrote:
> This is a workaround for sync polarity unstable.
> Sync value get by VR09C counts from sync's rising edge, which means
> sync's polarity is negative if sync value is bigger than total/2.

Do you have an example of such a format, or is this mostly theoretical?

Either provide the example or make a note that it is theoretical.

Regards,

	Hans

> 
> Signed-off-by: Jammy Huang <jammy_huang@...eedtech.com>
> ---
>  v2:
>   - Use 'total/2' rather than 'total<<1'
>   - Update comment
> ---
>  drivers/media/platform/aspeed-video.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/media/platform/aspeed-video.c b/drivers/media/platform/aspeed-video.c
> index 7c50567f5ab0..c3e3343d91e1 100644
> --- a/drivers/media/platform/aspeed-video.c
> +++ b/drivers/media/platform/aspeed-video.c
> @@ -989,6 +989,16 @@ static void aspeed_video_get_resolution(struct aspeed_video *video)
>  
>  		video->frame_bottom = FIELD_GET(VE_SRC_TB_EDGE_DET_BOT, src_tb_edge);
>  		video->frame_top = FIELD_GET(VE_SRC_TB_EDGE_DET_TOP, src_tb_edge);
> +
> +		/*
> +		 * This is a workaround for polarity detection when the sync
> +		 * value is larger than half.
> +		 */
> +		if (vsync > (vtotal / 2))
> +			det->polarities &= ~V4L2_DV_VSYNC_POS_POL;
> +		else
> +			det->polarities |= V4L2_DV_VSYNC_POS_POL;
> +
>  		if (det->polarities & V4L2_DV_VSYNC_POS_POL) {
>  			det->vbackporch = video->frame_top - vsync;
>  			det->vfrontporch = vtotal - video->frame_bottom;
> @@ -1003,6 +1013,16 @@ static void aspeed_video_get_resolution(struct aspeed_video *video)
>  
>  		video->frame_right = FIELD_GET(VE_SRC_LR_EDGE_DET_RT, src_lr_edge);
>  		video->frame_left = FIELD_GET(VE_SRC_LR_EDGE_DET_LEFT, src_lr_edge);
> +
> +		/*
> +		 * This is a workaround for polarity detection when the sync
> +		 * value is larger than half.
> +		 */
> +		if (hsync > (htotal / 2))
> +			det->polarities &= ~V4L2_DV_HSYNC_POS_POL;
> +		else
> +			det->polarities |= V4L2_DV_HSYNC_POS_POL;
> +
>  		if (det->polarities & V4L2_DV_HSYNC_POS_POL) {
>  			det->hbackporch = video->frame_left - hsync;
>  			det->hfrontporch = htotal - video->frame_right;