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

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Date:   Wed, 22 Dec 2021 01:22:36 +0000
From:   Joel Stanley <joel@....id.au>
To:     Jammy Huang <jammy_huang@...eedtech.com>
Cc:     Eddie James <eajames@...ux.ibm.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Andrew Jeffery <andrew@...id.au>, linux-media@...r.kernel.org,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] media: aspeed: Fix timing polarity incorrect

On Fri, 17 Dec 2021 at 09:54, Jammy Huang <jammy_huang@...eedtech.com> wrote:
>
> This is a workaround for 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.
>
> Signed-off-by: Jammy Huang <jammy_huang@...eedtech.com>
> ---
>  drivers/media/platform/aspeed-video.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/drivers/media/platform/aspeed-video.c b/drivers/media/platform/aspeed-video.c
> index 5ad3a20c5bac..f628f69bb7dd 100644
> --- a/drivers/media/platform/aspeed-video.c
> +++ b/drivers/media/platform/aspeed-video.c
> @@ -989,6 +989,15 @@ static void aspeed_video_get_resolution(struct aspeed_video *video)
>                 video->frame_top = FIELD_GET(VE_SRC_TB_EDGE_DET_TOP,
>                                              src_tb_edge);
>                 det->vsync = FIELD_GET(VE_SYNC_STATUS_VSYNC, sync);
> +               /*
> +                * Workaround for polarity detection
> +                * Use sync(VR098) counts from sync's rising edge till falling
> +                * edge to tell sync polarity.
> +                */
> +               if (det->vsync > (FIELD_GET(VE_MODE_DETECT_V_LINES, mds) >> 1))

Are you right shifting as this is the value / 2? I think it's clearer
to write / 2 instead of >> 1.

Mention in the comment that this is a workaround for when the sync
value is larger than half.

> +                       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 - det->vsync;
>                         det->vfrontporch =
> @@ -1010,6 +1019,15 @@ static void aspeed_video_get_resolution(struct aspeed_video *video)
>                 video->frame_left = FIELD_GET(VE_SRC_LR_EDGE_DET_LEFT,
>                                               src_lr_edge);
>                 det->hsync = FIELD_GET(VE_SYNC_STATUS_HSYNC, sync);
> +               /*
> +                * Workaround for polarity detection
> +                * Use sync(VR098) counts from sync's rising edge till falling
> +                * edge to tell sync polarity.
> +                */
> +               if (det->hsync > (htotal >> 1))
> +                       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 - det->hsync;
>                         det->hfrontporch = htotal - video->frame_right;
> --
> 2.25.1
>