linux-kernel - Re: [PATCH v3] drm/mediatek: adjust rdma fifo threshold calculate formula

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Message-ID: <CAAOTY_-15k_Fq4svKfaKukuYxc4DRfqP1kRudR9wgSrkc-+ZoQ@mail.gmail.com>
Date:   Mon, 12 Jul 2021 22:47:18 +0800
From:   Chun-Kuang Hu <chunkuang.hu@...nel.org>
To:     Yongqiang Niu <yongqiang.niu@...iatek.com>
Cc:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Fabien Parent <fparent@...libre.com>,
        Dennis YC Hsieh <dennis-yc.hsieh@...iatek.com>,
        DTML <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Project_Global_Chrome_Upstream_Group@...iatek.com,
        Hsin-Yi Wang <hsinyi@...omium.org>
Subject: Re: [PATCH v3] drm/mediatek: adjust rdma fifo threshold calculate formula

Hi, Yongqiang:

Yongqiang Niu <yongqiang.niu@...iatek.com> 於 2021年7月11日 週日 下午2:54寫道：
>
> the orginal formula will caused rdma fifo threshold config overflow
> and no one could come out a solution for all SoC,
> set threshold to 70% of max fifo size to make sure it will
> not overflow, and 70% is a empirical value

Applied to mediatek-drm-next [1], thanks.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git/log/?h=mediatek-drm-next

Regards,
Chun-Kuang.

>
> Signed-off-by: Yongqiang Niu <yongqiang.niu@...iatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_rdma.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> index f123fc0..f1f6a2e 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> @@ -164,10 +164,10 @@ void mtk_rdma_config(struct device *dev, unsigned int width,
>         /*
>          * Enable FIFO underflow since DSI and DPI can't be blocked.
>          * Keep the FIFO pseudo size reset default of 8 KiB. Set the
> -        * output threshold to 6 microseconds with 7/6 overhead to
> -        * account for blanking, and with a pixel depth of 4 bytes:
> +        * output threshold to 70% of max fifo size to make sure the
> +        * threhold will not overflow
>          */
> -       threshold = width * height * vrefresh * 4 * 7 / 1000000;
> +       threshold = rdma_fifo_size * 7 / 10;
>         reg = RDMA_FIFO_UNDERFLOW_EN |
>               RDMA_FIFO_PSEUDO_SIZE(rdma_fifo_size) |
>               RDMA_OUTPUT_VALID_FIFO_THRESHOLD(threshold);
> --
> 1.8.1.1.dirty
>