linux-kernel - Re: [PATCH v2 15/15] drm/mediatek: Introduce HDMI/DDC v2 for MT8195/MT8188

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Message-ID: <fm5rbujzu5og25x3nnxnhabrf4mppyy4nakxrskqtug774llnm@j47ce2zz6xsx>
Date: Tue, 17 Dec 2024 14:34:11 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: CK Hu (胡俊光) <ck.hu@...iatek.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>, "robh@...nel.org" <robh@...nel.org>, 
	"jie.qiu@...iatek.com" <jie.qiu@...iatek.com>, "kernel@...labora.com" <kernel@...labora.com>, 
	"simona@...ll.ch" <simona@...ll.ch>, "mripard@...nel.org" <mripard@...nel.org>, 
	"tzimmermann@...e.de" <tzimmermann@...e.de>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"conor+dt@...nel.org" <conor+dt@...nel.org>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, 
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>, 
	"maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>, "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>, 
	Jitao Shi (石记涛) <jitao.shi@...iatek.com>, "airlied@...il.com" <airlied@...il.com>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "matthias.bgg@...il.com" <matthias.bgg@...il.com>, 
	"junzhi.zhao@...iatek.com" <junzhi.zhao@...iatek.com>
Subject: Re: [PATCH v2 15/15] drm/mediatek: Introduce HDMI/DDC v2 for
 MT8195/MT8188

On Tue, Dec 17, 2024 at 06:40:11AM +0000, CK Hu (胡俊光) wrote:
> On Mon, 2024-12-16 at 12:04 +0100, AngeloGioacchino Del Regno wrote:
> > External email : Please do not click links or open attachments until you have verified the sender or the content.
> > 
> > 
> > Il 16/12/24 09:57, 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.
> > > > 
> > > > 
> > > > Add support for the newer HDMI-TX (Encoder) v2 and DDC v2 IPs
> > > > found in MediaTek's MT8195, MT8188 SoC and their variants, and
> > > > including support for display modes up to 4k60 and for HDMI
> > > > Audio, as per the HDMI 2.0 spec.
> > > > 
> > > > HDCP and CEC functionalities are also supported by this hardware,
> > > > but are not included in this commit and that also poses a slight
> > > > difference between the V2 and V1 controllers in how they handle
> > > > Hotplug Detection (HPD).
> > > > 
> > > > While the v1 controller was using the CEC controller to check
> > > > HDMI cable connection and disconnection, in this driver the v2
> > > > one does not.
> > > > 
> > > > This is due to the fact that on parts with v2 designs, like the
> > > > MT8195 SoC, there is one CEC controller shared between the HDMI
> > > > Transmitter (HDMI-TX) and Receiver (HDMI-RX): before eventually
> > > > adding support to use the CEC HW to wake up the HDMI controllers
> > > > it is necessary to have support for one TX, one RX *and* for both
> > > > at the same time.
> > > > 
> > > > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> > > > ---
> > > 
> > > [snip]
> > > 
> > > > +static int mtk_hdmi_v2_bridge_atomic_check(struct drm_bridge *bridge,
> > > > +                                          struct drm_bridge_state *bridge_state,
> > > > +                                          struct drm_crtc_state *crtc_state,
> > > > +                                          struct drm_connector_state *conn_state)
> > > > +{
> > > 
> > > I would like v1 and v2 has the same behavior.
> > > Why v2 has atomic check but v1 has no?
> > > If this is better to have, add atomic check to v1, and this function would be common function.
> > > 
> > 
> > That's because v2 uses the new helpers, while v1 does not.
> > The v1 must be converted to the new helpers in order to use atomic_check() like v2.
> 
> I just find the description here, and I don't know why new helper need atomic_check().
> Would you provide more information how new helper need atomic_check()?

The HDMI helpers requires the driver to use
drm_atomic_helper_connector_hdmi_check() in order to maintain
HDMI-specific connector and CRTC state. Thus drivers using HDMI
Connector framework have to provide .atomic_check() callback which calls
the mentioned function.

> For example, the call stack to atomic_check(). (You could use dump_stack() to show it)

-- 
With best wishes
Dmitry