linux-kernel - Re: [PATCH v12 6/8] drm/mediatek: enable dither function

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Date:   Fri, 29 Jan 2021 09:33:02 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
CC:     Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <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>,
        Yongqiang Niu <yongqiang.niu@...iatek.com>
Subject: Re: [PATCH v12 6/8] drm/mediatek: enable dither function

Hi, Hsin-Yi:

On Thu, 2021-01-28 at 19:23 +0800, Hsin-Yi Wang wrote:
> From: Yongqiang Niu <yongqiang.niu@...iatek.com>
> 
> for 5 or 6 bpc panel, we need enable dither function
> to improve the display quality
> 
> Signed-off-by: Yongqiang Niu <yongqiang.niu@...iatek.com>
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> ---
>  drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> index ac2cb25620357..6c8f246380a74 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> @@ -53,6 +53,7 @@
>  #define DITHER_EN				BIT(0)
>  #define DISP_DITHER_CFG				0x0020
>  #define DITHER_RELAY_MODE			BIT(0)
> +#define DITHER_ENGINE_EN			BIT(1)
>  #define DISP_DITHER_SIZE			0x0030
>  
>  #define LUT_10BIT_MASK				0x03ff
> @@ -314,9 +315,19 @@ static void mtk_dither_config(struct device *dev, unsigned int w,
>  			      unsigned int bpc, struct cmdq_pkt *cmdq_pkt)
>  {
>  	struct mtk_ddp_comp_dev *priv = dev_get_drvdata(dev);
> +	bool enable = (bpc == 5 || bpc == 6);

I strongly believe that dither function in dither is identical to the
one in gamma and od, and in mtk_dither_set_common(), 'bpc >=
MTK_MIN_BPC' is valid, so I believe we need not to limit bpc to 5 or 6.
But we should consider the case that bpc is invalid in
mtk_dither_set_common(). Invalid case in gamma and od use different way
to process. For gamma, dither is default relay mode, so invalid bpc
would do nothing in mtk_dither_set_common() and result in relay mode.
For od, it set to relay mode first, them invalid bpc would do nothing in
mtk_dither_set_common() and result in relay mode. I would like dither,
gamma and od to process invalid bpc in the same way. One solution is to
set relay mode in mtk_dither_set_common() for invalid bpc.

Regards,
CK

>  
> -	mtk_ddp_write(cmdq_pkt, h << 16 | w, &priv->cmdq_reg, priv->regs, DISP_DITHER_SIZE);
> -	mtk_ddp_write(cmdq_pkt, DITHER_RELAY_MODE, &priv->cmdq_reg, priv->regs, DISP_DITHER_CFG);
> +	if (enable) {
> +		mtk_dither_set_common(priv->regs, &priv->cmdq_reg, bpc,
> +				      DISP_DITHER_CFG, DITHER_ENGINE_EN,
> +				      cmdq_pkt);
> +	} else {
> +		mtk_ddp_write(cmdq_pkt, DITHER_RELAY_MODE, &priv->cmdq_reg,
> +			      priv->regs, DISP_DITHER_CFG);
> +	}
> +
> +	mtk_ddp_write(cmdq_pkt, h << 16 | w, &priv->cmdq_reg, priv->regs,
> +		      DISP_DITHER_SIZE);
>  }
>  
>  static void mtk_dither_start(struct device *dev)