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Date:   Tue, 16 Apr 2019 16:00:47 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     <yongqiang.niu@...iatek.com>
CC:     <p.zabel@...gutronix.de>, <robh+dt@...nel.org>,
        <matthias.bgg@...il.com>, <airlied@...ux.ie>,
        <mark.rutland@....com>, <dri-devel@...ts.freedesktop.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <Bibby.Hsieh@...iatek.com>,
        <yt.shen@...iatek.com>
Subject: Re: [PATCH v2 18/25] drm/mediatek: add RDMA fifo size error handle

Hi, Yongqiang:

On Wed, 2019-03-27 at 14:19 +0800, yongqiang.niu@...iatek.com wrote:
> From: Yongqiang Niu <yongqiang.niu@...iatek.com>
> 
> This patch add RDMA fifo size error handle
> rdma fifo size will not always bigger than the calculated threshold
> if that case happened, we need set fifo size as the threshold
> 
> Signed-off-by: Yongqiang Niu <yongqiang.niu@...iatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_rdma.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> index b0a5cff..ead38ba 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> @@ -137,11 +137,14 @@ static void mtk_rdma_config(struct mtk_ddp_comp *comp, unsigned int width,
>  {
>  	unsigned int threshold;
>  	unsigned int reg;
> +	unsigned int rdma_fifo_size;
>  	struct mtk_disp_rdma *rdma = comp_to_rdma(comp);
>  
>  	rdma_update_bits(comp, DISP_REG_RDMA_SIZE_CON_0, 0xfff, width);
>  	rdma_update_bits(comp, DISP_REG_RDMA_SIZE_CON_1, 0xfffff, height);
>  
> +	rdma_fifo_size = RDMA_FIFO_SIZE(rdma);
> +
>  	/*
>  	 * Enable FIFO underflow since DSI and DPI can't be blocked.
>  	 * Keep the FIFO pseudo size reset default of 8 KiB. Set the
> @@ -149,8 +152,12 @@ static void mtk_rdma_config(struct mtk_ddp_comp *comp, unsigned int width,
>  	 * account for blanking, and with a pixel depth of 4 bytes:
>  	 */
>  	threshold = width * height * vrefresh * 4 * 7 / 1000000;
> +
> +	if (threshold > rdma_fifo_size)
> +		threshold = rdma_fifo_size;

I think this is a work around not a correct solution. Why MT8173 has no
this problem but MT8183 has? Is the formula of threshold different in
MT8173 and MT8183?

Regards,
CK

> +
>  	reg = RDMA_FIFO_UNDERFLOW_EN |
> -	      RDMA_FIFO_PSEUDO_SIZE(RDMA_FIFO_SIZE(rdma)) |
> +	      RDMA_FIFO_PSEUDO_SIZE(rdma_fifo_size) |
>  	      RDMA_OUTPUT_VALID_FIFO_THRESHOLD(threshold);
>  	writel(reg, comp->regs + DISP_REG_RDMA_FIFO_CON);
>  }


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