linux-kernel - Re: [PATCH v2 13/15] drm/mediatek: mtk_hdmi_common: Assign DDC adapter pointer to bridge

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Message-ID: <b5a77637-64b0-4ed3-9619-e76d094505af@collabora.com>
Date: Mon, 9 Dec 2024 10:49:28 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: CK Hu (胡俊光) <ck.hu@...iatek.com>,
 "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>
Cc: "robh@...nel.org" <robh@...nel.org>,
 "jie.qiu@...iatek.com" <jie.qiu@...iatek.com>,
 "tzimmermann@...e.de" <tzimmermann@...e.de>,
 "simona@...ll.ch" <simona@...ll.ch>, "mripard@...nel.org"
 <mripard@...nel.org>, Jitao Shi (石记涛)
 <jitao.shi@...iatek.com>,
 "linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
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Subject: Re: [PATCH v2 13/15] drm/mediatek: mtk_hdmi_common: Assign DDC
 adapter pointer to bridge

Il 09/12/24 09:17, CK Hu (胡俊光) ha scritto:
> Hi, Angelo:
> 
> On Thu, 2024-12-05 at 12:45 +0100, AngeloGioacchino Del Regno wrote:
>> External email : Please do not click links or open attachments until you have verified the sender or the content.
>>
>>
>> In preparation for adding the new HDMI TX v2 IP driver, assign the
>> pointer to the DDC adapter to struct drm_bridge during probe.
>>
>> This commit brings no functional changes.
>>
>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>>   drivers/gpu/drm/mediatek/mtk_hdmi_common.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi_common.c b/drivers/gpu/drm/mediatek/mtk_hdmi_common.c
>> index 1b23ab6969ec..4f708b04f5e8 100644
>> --- a/drivers/gpu/drm/mediatek/mtk_hdmi_common.c
>> +++ b/drivers/gpu/drm/mediatek/mtk_hdmi_common.c
>> @@ -410,6 +410,7 @@ struct mtk_hdmi *mtk_hdmi_common_probe(struct platform_device *pdev)
>>          hdmi->bridge.ops = DRM_BRIDGE_OP_DETECT | DRM_BRIDGE_OP_EDID | DRM_BRIDGE_OP_HPD;
>>          hdmi->bridge.type = DRM_MODE_CONNECTOR_HDMIA;
>>          hdmi->bridge.of_node = pdev->dev.of_node;
>> +       hdmi->bridge.ddc = hdmi->ddc_adpt;
> 
> I don't know why only v2 driver need to assign this?
> Could you point out the code where access this value?
> 

v2 uses hdmi helpers, which make use of bridge->ddc.
mtk_hdmi_v2_bridge_edid_read() calls drm_edid_read().

drm_edid.c -> drm_edid_read()
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/drm_edid.c?h=next-20241209#n2704

...while v1 feeds the (internal) ddc pointer to drm_edid_read_ddc() instead.

Cheers,
Angelo

> Regards,
> CK
> 
>>
>>          ret = devm_drm_bridge_add(dev, &hdmi->bridge);
>>          if (ret)
>> --
>> 2.47.0
>>
>