linux-kernel - Re: [PATCH] drm/mediatek: mtk-dpi: Set out_fmt from config if not the last bridge

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Date:   Fri, 16 Jul 2021 13:46:52 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
CC:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Jitao Shi <jitao.shi@...iatek.com>,
        David Airlie <airlied@...ux.ie>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        Rex-BC Chen <rex-bc.chen@...iatek.com>,
        <linux-mediatek@...ts.infradead.org>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] drm/mediatek: mtk-dpi: Set out_fmt from config if not
 the last bridge

Hi, Hsin-yi:

On Mon, 2021-07-12 at 17:46 +0800, Hsin-Yi Wang wrote:
> atomic_get_output_bus_fmts() is only called when the bridge is the last
> element in the bridge chain.
> 
> If mtk-dpi is not the last bridge, the format of output_bus_cfg is
> MEDIA_BUS_FMT_FIXED, and mtk_dpi_dual_edge() will fail to write correct
> value to regs.

Reviewed-by: CK Hu <ck.hu@...iatek.com>

> 
> Fixes: ec8747c52434 ("drm/mediatek: dpi: Add bus format negotiation")
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> ---
>  drivers/gpu/drm/mediatek/mtk_dpi.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dpi.c b/drivers/gpu/drm/mediatek/mtk_dpi.c
> index bced555648b01..25c565f9179cc 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dpi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dpi.c
> @@ -610,6 +610,10 @@ static int mtk_dpi_bridge_atomic_check(struct drm_bridge *bridge,
>  
>  	out_bus_format = bridge_state->output_bus_cfg.format;
>  
> +	if (out_bus_format == MEDIA_BUS_FMT_FIXED)
> +		if (dpi->conf->num_output_fmts)
> +			out_bus_format = dpi->conf->output_fmts[0];
> +
>  	dev_dbg(dpi->dev, "input format 0x%04x, output format 0x%04x\n",
>  		bridge_state->input_bus_cfg.format,
>  		bridge_state->output_bus_cfg.format);