[v3 PATCH] drm/mediatek: dsi: fix scrolling of panel with small hfp or hbp

[Bilal Wasim]

Hi Jitao, 

On Thu, 17 Sep 2020 11:30:09 +0800
Jitao Shi <jitao.shi at mediatek.com> wrote:

> Replace horizontal_backporch_byte with vm->hback_porch * bpp to aovid
> flowing judgement negative number.
> 
> if ((vm->hfront_porch * dsi_tmp_buf_bpp + horizontal_backporch_byte) >
> 	data_phy_cycles * dsi->lanes + delta)
> 
> Signed-off-by: Jitao Shi <jitao.shi at mediatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_dsi.c | 54
> ++++++++++++++------------------------ 1 file changed, 19
> insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c
> b/drivers/gpu/drm/mediatek/mtk_dsi.c index 16fd99dcdacf..ddddf69ebeaf
> 100644 --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -445,6 +445,7 @@ static void mtk_dsi_config_vdo_timing(struct
> mtk_dsi *dsi) u32 horizontal_backporch_byte;
>  	u32 horizontal_frontporch_byte;
>  	u32 dsi_tmp_buf_bpp, data_phy_cycles;
> +	u32 delta;
>  	struct mtk_phy_timing *timing = &dsi->phy_timing;
>  
>  	struct videomode *vm = &dsi->vm;
> @@ -475,42 +476,25 @@ static void mtk_dsi_config_vdo_timing(struct
> mtk_dsi *dsi) data_phy_cycles = timing->lpx + timing->da_hs_prepare +
>  			  timing->da_hs_zero + timing->da_hs_exit +
> 3; 
> -	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;
> -		}
> +	delta = (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) ? 18 :
> 12; +
> +	if ((vm->hfront_porch * dsi_tmp_buf_bpp +
> horizontal_backporch_byte) >
> +	    data_phy_cycles * dsi->lanes + delta) {
> +		horizontal_frontporch_byte =
> +			vm->hfront_porch * dsi_tmp_buf_bpp -
> +			(data_phy_cycles * dsi->lanes + delta) *
> +			vm->hfront_porch /
> +			(vm->hfront_porch + vm->hback_porch);
> +
> +		horizontal_backporch_byte =
> +			horizontal_backporch_byte -
> +			(data_phy_cycles * dsi->lanes + delta) *
> +			vm->hback_porch /
> +			(vm->hfront_porch + vm->hback_porch);
>  	} 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");
> +		horizontal_frontporch_byte = vm->hfront_porch *
> +					     dsi_tmp_buf_bpp;
>  	}
>  
>  	writel(horizontal_sync_active_byte, dsi->regs + DSI_HSA_WC);

Can you explain how this patch is relevant to
https://patchwork.kernel.org/patch/11718191/? It was sent out on
17/Sept while the v2 was merged before that. 

As the v2 patch (https://patchwork.kernel.org/patch/11718191/) breaks
HDMI (eDP) on my Chromebook Elm (starting from 5.9-rc6), I'm guessing
that that was a bad patch, and should be reverted? Instead, this v3
should be applied? Is this correct? 

If so, can you kindly send a new patch which reverts v2 and applies
this one, as application of this patch on rc7 fails.

Thanks,
Bilal