linux-kernel - Re: [PATCH v11 05/11] drm/mediatek: mtk_hdmi

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Message-ID: <CAAOTY_8y6C5=jSjzBVVJ2vJq1L+Nf9U0tZvxzVX-e-3g91xEeQ@mail.gmail.com>
Date: Thu, 23 Oct 2025 15:59:17 +0000
From: Chun-Kuang Hu <chunkuang.hu@...nel.org>
To: Louis-Alexis Eyraud <louisalexis.eyraud@...labora.com>
Cc: Chun-Kuang Hu <chunkuang.hu@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, CK Hu <ck.hu@...iatek.com>, 
	kernel@...labora.com, dri-devel@...ts.freedesktop.org, 
	linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v11 05/11] drm/mediatek: mtk_hdmi_common: Make CEC support optional

Hi, Louis:

Louis-Alexis Eyraud <louisalexis.eyraud@...labora.com> 於 2025年10月23日
週四 上午10:32寫道：
>
> From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>
> In preparation for adding a new driver for HDMIv2, for which CEC
> is not strictly required, change the of_get_compatible_child()
> failure error to -ENOTSUPP to be able to differentiate between
> error conditions in mtk_hdmi_dt_parse_pdata().
>
> In that case, if -ENOTSUPP is returned, this driver will print
> an informative message saying that CEC support is unavailable,
> as the devicetree node for that was not found, but after that,
> function mtk_hdmi_dt_parse_pdata() will not return error to
> the caller.
>
> This will not change functionality of the mtk_hdmi (v1) driver
> as that is still checking whether CEC is present and, if not,
> will fail probing with an error saying that CEC is required
> by HDMIv1.
>
> Reviewed-by: CK Hu <ck.hu@...iatek.com>
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@...labora.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_hdmi_common.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi_common.c b/drivers/gpu/drm/mediatek/mtk_hdmi_common.c
> index f28e63716d7c2e2c6bdf5b28d24789bc926d2beb..989479fdfe40952762a1b63797bf602b520dcac5 100644
> --- a/drivers/gpu/drm/mediatek/mtk_hdmi_common.c
> +++ b/drivers/gpu/drm/mediatek/mtk_hdmi_common.c
> @@ -253,12 +253,11 @@ static int mtk_hdmi_get_cec_dev(struct mtk_hdmi *hdmi, struct device *dev, struc
>         /* The CEC module handles HDMI hotplug detection */
>         cec_np = of_get_compatible_child(np->parent, "mediatek,mt8173-cec");
>         if (!cec_np)
> -               return dev_err_probe(dev, -EINVAL, "Failed to find CEC node\n");
> +               return dev_err_probe(dev, -ENOTSUPP, "Failed to find CEC node\n");

The checkpatch show the warning:

WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP
#40: FILE: drivers/gpu/drm/mediatek/mtk_hdmi_common.c:256:
+        return dev_err_probe(dev, -ENOTSUPP, "Failed to find CEC node\n");

I find many driver use ENOTSUPP, so I'm not sure which one is better.
I really don't understand the description about these two error code [1].
If you choose ENOTSUPP, please give me some explain.

[1] https://man7.org/linux/man-pages/man3/errno.3.html

Regards,
Chun-Kuang.

>
>         cec_pdev = of_find_device_by_node(cec_np);
>         if (!cec_pdev) {
> -               dev_err(hdmi->dev, "Waiting for CEC device %pOF\n",
> -                       cec_np);
> +               dev_err(hdmi->dev, "Waiting for CEC device %pOF\n", cec_np);
>                 of_node_put(cec_np);
>                 return -EPROBE_DEFER;
>         }
> @@ -319,7 +318,9 @@ static int mtk_hdmi_dt_parse_pdata(struct mtk_hdmi *hdmi, struct platform_device
>                 return dev_err_probe(dev, -EINVAL, "Failed to get ddc i2c adapter by node\n");
>
>         ret = mtk_hdmi_get_cec_dev(hdmi, dev, np);
> -       if (ret)
> +       if (ret == -ENOTSUPP)
> +               dev_info(dev, "CEC support unavailable: node not found\n");
> +       else if (ret)
>                 return ret;
>
>         return 0;
>
> --
> 2.51.0
>