linux-kernel - Re: [v10,2/3] drm/mediatek: implement the DSI HS packets aligned

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Date:   Wed, 19 Jan 2022 09:35:01 +0100
From:   Andrzej Hajda <andrzej.hajda@...el.com>
To:     Rex-BC Chen <rex-bc.chen@...iatek.com>, <chunkuang.hu@...nel.org>,
        <matthias.bgg@...il.com>, <narmstrong@...libre.com>,
        <robert.foss@...aro.org>, <daniel@...ll.ch>, <airlied@...ux.ie>,
        <p.zabel@...gutronix.de>
CC:     <xji@...logixsemi.com>, <jitao.shi@...iatek.com>,
        <xinlei.lee@...iatek.com>,
        <angelogioacchino.delregno@...labora.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [v10,2/3] drm/mediatek: implement the DSI HS packets aligned


On 19.01.2022 03:25, Rex-BC Chen wrote:
> Some DSI RX devices (for example, anx7625) require last alignment of
> packets on all lanes after each row of data is sent.
> Otherwise, there will be some issues of shift or scroll for screen.
>
> Take horizontal_sync_active_byte for a example,
> we roundup the HSA packet data to lane number, and the subtraction of 2
> is the packet data value added by the roundup operation, making the
> long packets are integer multiples of lane number.
> This value (2) varies with the lane number, and that is the reason we
> do this operation when the lane number is 4.
>
> In the previous operation of function "mtk_dsi_config_vdo_timing",
> the length of HSA and HFP data packets has been adjusted to an
> integration multiple of lane number.
> Since the number of RGB data packets cannot be guaranteed to be an
> integer multiple of lane number, we modify the data packet length of
> HBP so that the number of HBP + RGB is equal to the lane number.
> So after sending a line of data (HSA + HBP + RGB + HFP), the data
> lanes are aligned.
>
> Signed-off-by: Jitao Shi <jitao.shi@...iatek.com>
> Signed-off-by: Rex-BC Chen <rex-bc.chen@...iatek.com>
> Signed-off-by: Xinlei Lee <xinlei.lee@...iatek.com>

Reviewed-by: Andrzej Hajda <andrzej.hajda@...el.com>

Regards

Andrzej

> ---
>   drivers/gpu/drm/mediatek/mtk_dsi.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index 5d90d2eb0019..e91b3fff4342 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -500,6 +500,18 @@ static void mtk_dsi_config_vdo_timing(struct mtk_dsi *dsi)
>   		DRM_WARN("HFP + HBP less than d-phy, FPS will under 60Hz\n");
>   	}
>   
> +	if ((dsi->mode_flags & MIPI_DSI_HS_PKT_END_ALIGNED) &&
> +	    (dsi->lanes == 4)) {
> +		horizontal_sync_active_byte =
> +			roundup(horizontal_sync_active_byte, dsi->lanes) - 2;
> +		horizontal_frontporch_byte =
> +			roundup(horizontal_frontporch_byte, dsi->lanes) - 2;
> +		horizontal_backporch_byte =
> +			roundup(horizontal_backporch_byte, dsi->lanes) - 2;
> +		horizontal_backporch_byte -=
> +			(vm->hactive * dsi_tmp_buf_bpp + 2) % dsi->lanes;
> +	}
> +
>   	writel(horizontal_sync_active_byte, dsi->regs + DSI_HSA_WC);
>   	writel(horizontal_backporch_byte, dsi->regs + DSI_HBP_WC);
>   	writel(horizontal_frontporch_byte, dsi->regs + DSI_HFP_WC);