linux-kernel - Re: [PATCH 2/3] drm/panel: Add support for the Leadtek LTK08QV25BYL panel

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Message-ID: <20251104094937.042afc40@bootlin.com>
Date: Tue, 4 Nov 2025 09:49:37 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Neil Armstrong <neil.armstrong@...aro.org>
Cc: Jessica Zhang <jessica.zhang@....qualcomm.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 2/3] drm/panel: Add support for the Leadtek LTK08QV25BYL
 panel

Hi Neil,

On Wed, 29 Oct 2025 21:45:24 +0100
Neil Armstrong <neil.armstrong@...aro.org> wrote:

...

> > +
> > +static const struct drm_display_mode ltk028qv25byl_mode = {
> > +	.hdisplay       = 240,
> > +	.hsync_start    = 240 + 120,
> > +	.hsync_end      = 240 + 120 + 4,
> > +	.htotal         = 240 + 120 + 4 + 120,
> > +	.vdisplay       = 320,
> > +	.vsync_start    = 320 + 8,
> > +	.vsync_end      = 320 + 8 + 2,
> > +	.vtotal         = 320 + 8 + 2 + 6,
> > +	.clock          = 10000000 / 1000,  
> 
> Usually we calculate the clock from the mode parameters, won't it work here ?
> 

The panel has an internal oscillator an the data transfer need to be sync with
this oscillator.

10M pixel per sec is the value set by the vendor.
I tried to use a value based on other mode parameters such as
  (240 + 120 + 4 + 120) * (320 + 8 + 2 + 6) * 60 / 1000

and it didn't work. I also tried ' ... * 90 / 1000) and ' ... * 100 / 1000)
without better results.

I can add a comment if you want in the next iteration to spot the value:
--- 8< ---
	.clock          = 10000000 / 1000,  /* 10 Mbps, internal panel oscillator */
--- 8< ---

Let me know.


...

> > +	ctx->iovcc = devm_regulator_get(dev, "iovcc");
> > +	if (IS_ERR(ctx->iovcc))
> > +		return dev_err_probe(dev, PTR_ERR(ctx->iovcc),
> > +				     "Failed to get iovcc regulator\n");  
> 
> Can you switch to devm_regulator_bulk_get_const() ?

Yes, I will do that in the next iteration.

Best regards,
Hervé