linux-kernel - Re: [PATCH v3 12/15] drm/bridge: Add ITE IT6263 LVDS to HDMI converter

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Message-ID: <20241022-wondrous-fractal-lion-aedcd9@houat>
Date: Tue, 22 Oct 2024 09:53:44 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Liu Ying <victor.liu@....com>
Cc: dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, imx@...ts.linux.dev, 
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Subject: Re: [PATCH v3 12/15] drm/bridge: Add ITE IT6263 LVDS to HDMI
 converter

On Tue, Oct 22, 2024 at 03:36:47PM +0800, Liu Ying wrote:
> Hi Maxime,
> 
> On 10/21/2024, Maxime Ripard wrote:
> > On Mon, Oct 21, 2024 at 02:44:43PM +0800, Liu Ying wrote:
> >> +static int it6263_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)
> >> +{
> >> +	struct drm_display_mode *mode = &crtc_state->adjusted_mode;
> >> +	int ret;
> >> +
> >> +	ret = drm_atomic_helper_connector_hdmi_check(conn_state->connector,
> >> +						     conn_state->state);
> >> +	if (ret)
> >> +		return ret;
> >> +
> >> +	return mode->clock > MAX_PIXEL_CLOCK_KHZ ? -EINVAL : 0;
> > 
> > drm_atomic_helper_connector_hdmi_check will already make that check, so
> > it's redundant.
> 
> MAX_PIXEL_CLOCK_KHZ is 150MHz. With 150MHz pixel clock rate, we'll get
> 150MHz HDMI character rate for 8bpc and 187.5MHz HDMI character rate
> for 10bpc, both are lower than MAX_HDMI_TMDS_CHAR_RATE_HZ = 225MHz.

I guess? I have no idea how that's relevant though. Where are those
constraints coming from, and why aren't you checking for them in
tmds_char_rate_valid?

> So, it looks like pixel clock rate is the bottleneck.

The bottleneck to what?

> Remove drm_atomic_helper_connector_hdmi_check() or keep this as-is?

No, like I said, remove the final check for mode->clock.

Maxime

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