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Date:   Fri, 20 Nov 2020 05:29:50 +0500
From:   Bilal Wasim <bilalwasim676@...il.com>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>
Cc:     Jitao Shi <jitao.shi@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org, CK Hu <ck.hu@...iatek.com>
Subject: Re: [PATCH] drm/mediatek: dsi: Modify horizontal front/back porch
 byte formula

Hi CK, 

On Fri, 20 Nov 2020 07:23:35 +0800
Chun-Kuang Hu <chunkuang.hu@...nel.org> wrote:

> From: CK Hu <ck.hu@...iatek.com>
> 
> In the patch to be fixed, horizontal_backporch_byte become to large
> for some panel, so roll back that patch. For small hfp or hbp panel,
> using vm->hfront_porch + vm->hback_porch to calculate
> horizontal_backporch_byte would make it negtive, so
> use horizontal_backporch_byte itself to make it positive.
> 
> Fixes: 35bf948f1edb ("drm/mediatek: dsi: Fix scrolling of panel with
> small hfp or hbp")
> 
> Signed-off-by: CK Hu <ck.hu@...iatek.com>
> Signed-off-by: Chun-Kuang Hu <chunkuang.hu@...nel.org>
> ---
>  drivers/gpu/drm/mediatek/mtk_dsi.c | 61
> +++++++++++------------------- 1 file changed, 22 insertions(+), 39
> deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c
> b/drivers/gpu/drm/mediatek/mtk_dsi.c index 4a188a942c38..65fd99c528af
> 100644 --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -444,7 +444,10 @@ static void mtk_dsi_config_vdo_timing(struct
> mtk_dsi *dsi) u32 horizontal_sync_active_byte;
>  	u32 horizontal_backporch_byte;
>  	u32 horizontal_frontporch_byte;
> +	u32 horizontal_front_back_byte;
> +	u32 data_phy_cycles_byte;
>  	u32 dsi_tmp_buf_bpp, data_phy_cycles;
> +	u32 delta;
>  	struct mtk_phy_timing *timing = &dsi->phy_timing;
>  
>  	struct videomode *vm = &dsi->vm;
> @@ -466,50 +469,30 @@ static void mtk_dsi_config_vdo_timing(struct
> mtk_dsi *dsi) horizontal_sync_active_byte = (vm->hsync_len *
> dsi_tmp_buf_bpp - 10); 
>  	if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE)
> -		horizontal_backporch_byte = vm->hback_porch *
> dsi_tmp_buf_bpp;
> +		horizontal_backporch_byte = vm->hback_porch *
> dsi_tmp_buf_bpp - 10; else
>  		horizontal_backporch_byte = (vm->hback_porch +
> vm->hsync_len) *
> -					    dsi_tmp_buf_bpp;
> +					    dsi_tmp_buf_bpp - 10;
>  
>  	data_phy_cycles = timing->lpx + timing->da_hs_prepare +
> -			  timing->da_hs_zero + timing->da_hs_exit;
> -
> -	if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) {
> -		if ((vm->hfront_porch + vm->hback_porch) *
> dsi_tmp_buf_bpp >
> -		    data_phy_cycles * dsi->lanes + 18) {
> -			horizontal_frontporch_byte =
> -				vm->hfront_porch * dsi_tmp_buf_bpp -
> -				(data_phy_cycles * dsi->lanes + 18) *
> -				vm->hfront_porch /
> -				(vm->hfront_porch + vm->hback_porch);
> -
> -			horizontal_backporch_byte =
> -				horizontal_backporch_byte -
> -				(data_phy_cycles * dsi->lanes + 18) *
> -				vm->hback_porch /
> -				(vm->hfront_porch + vm->hback_porch);
> -		} else {
> -			DRM_WARN("HFP less than d-phy, FPS will
> under 60Hz\n");
> -			horizontal_frontporch_byte =
> vm->hfront_porch *
> -						     dsi_tmp_buf_bpp;
> -		}
> +			  timing->da_hs_zero + timing->da_hs_exit +
> 3; +
> +	delta = dsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST ? 18 :
> 12; +
> +	horizontal_frontporch_byte = vm->hfront_porch *
> dsi_tmp_buf_bpp;
> +	horizontal_front_back_byte = horizontal_frontporch_byte +
> horizontal_backporch_byte;
> +	data_phy_cycles_byte = data_phy_cycles * dsi->lanes + delta;
> +
> +	if (horizontal_front_back_byte > data_phy_cycles_byte) {
> +		horizontal_frontporch_byte -= data_phy_cycles_byte *
> +
> horizontal_frontporch_byte /
> +
> horizontal_front_back_byte; +
> +		horizontal_backporch_byte -= data_phy_cycles_byte *
> +
> horizontal_backporch_byte /
> +
> horizontal_front_back_byte; } else {
> -		if ((vm->hfront_porch + vm->hback_porch) *
> dsi_tmp_buf_bpp >
> -		    data_phy_cycles * dsi->lanes + 12) {
> -			horizontal_frontporch_byte =
> -				vm->hfront_porch * dsi_tmp_buf_bpp -
> -				(data_phy_cycles * dsi->lanes + 12) *
> -				vm->hfront_porch /
> -				(vm->hfront_porch + vm->hback_porch);
> -			horizontal_backporch_byte =
> horizontal_backporch_byte -
> -				(data_phy_cycles * dsi->lanes + 12) *
> -				vm->hback_porch /
> -				(vm->hfront_porch + vm->hback_porch);
> -		} else {
> -			DRM_WARN("HFP less than d-phy, FPS will
> under 60Hz\n");
> -			horizontal_frontporch_byte =
> vm->hfront_porch *
> -						     dsi_tmp_buf_bpp;
> -		}
> +		DRM_WARN("HFP + HBP less than d-phy, FPS will under
> 60Hz\n"); }
>  
>  	writel(horizontal_sync_active_byte, dsi->regs + DSI_HSA_WC);

Tested on Chromebook ELM.

Tested-by: Bilal Wasim <bilal.wasim@...tec.com>

Thanks,
Bilal

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