linux-kernel - Re: [PATCH v15 2/8] phy: Add HDMI configuration options

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Date: Fri, 5 Apr 2024 18:09:48 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Vinod Koul <vkoul@...nel.org>
Cc: Maxime Ripard <mripard@...nel.org>, 
	Alexander Stein <alexander.stein@...tq-group.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Kishon Vijay Abraham I <kishon@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, Sandor Yu <Sandor.yu@....com>, dri-devel@...ts.freedesktop.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org, 
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, linux@...tq-group.com
Subject: Re: [PATCH v15 2/8] phy: Add HDMI configuration options

On Fri, Apr 05, 2024 at 07:54:46PM +0530, Vinod Koul wrote:
> On 06-03-24, 15:48, Maxime Ripard wrote:
> > Hi Alexander,
> > 
> > On Wed, Mar 06, 2024 at 11:16:19AM +0100, Alexander Stein wrote:
> > > From: Sandor Yu <Sandor.yu@....com>
> > > 
> > > Allow HDMI PHYs to be configured through the generic
> > > functions through a custom structure added to the generic union.
> > > 
> > > The parameters added here are based on HDMI PHY
> > > implementation practices.  The current set of parameters
> > > should cover the potential users.
> > > 
> > > Signed-off-by: Sandor Yu <Sandor.yu@....com>
> > > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > > Acked-by: Vinod Koul <vkoul@...nel.org>
> > > ---
> > >  include/linux/phy/phy-hdmi.h | 24 ++++++++++++++++++++++++
> > >  include/linux/phy/phy.h      |  7 ++++++-
> > >  2 files changed, 30 insertions(+), 1 deletion(-)
> > >  create mode 100644 include/linux/phy/phy-hdmi.h
> > > 
> > > diff --git a/include/linux/phy/phy-hdmi.h b/include/linux/phy/phy-hdmi.h
> > > new file mode 100644
> > > index 0000000000000..b7de88e9090f0
> > > --- /dev/null
> > > +++ b/include/linux/phy/phy-hdmi.h
> > > @@ -0,0 +1,24 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > +/*
> > > + * Copyright 2022 NXP
> > > + */
> > > +
> > > +#ifndef __PHY_HDMI_H_
> > > +#define __PHY_HDMI_H_
> > > +
> > > +#include <linux/hdmi.h>
> > > +/**
> > > + * struct phy_configure_opts_hdmi - HDMI configuration set
> > > + * @pixel_clk_rate: Pixel clock of video modes in KHz.
> > > + * @bpc: Maximum bits per color channel.
> > > + * @color_space: Colorspace in enum hdmi_colorspace.
> > > + *
> > > + * This structure is used to represent the configuration state of a HDMI phy.
> > > + */
> > > +struct phy_configure_opts_hdmi {
> > > +	unsigned int pixel_clk_rate;
> > > +	unsigned int bpc;
> > > +	enum hdmi_colorspace color_space;
> > > +};
> > 
> > Does the PHY actually care about the pixel clock rate, color space and
> > formats, or does it only care about the character rate?
> 
> Nope it should not

After taking a look at the Cadence PHY driver, I share the feeling that
hdptx_hdmi_feedback_factor() should be reworked into drm_display helper
and then the struct phy_configure_opts_hdmi can be limited to having a
single unsigned long char_freq or bit_rate field.

I'm not sure whether we need anything corresponding to the TMDS Bit
Clock Ratio control. As far as I understand, it can be deduced from the
Bit Rate.

-- 
With best wishes
Dmitry