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

From: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
To: Vinod Koul <vkoul@kernel.org>
Cc: Maxime Ripard <mripard@kernel.org>,
	 Alexander Stein <alexander.stein@ew.tq-group.com>,
	Andrzej Hajda <andrzej.hajda@intel.com>,
	 Neil Armstrong <neil.armstrong@linaro.org>,
	Robert Foss <rfoss@kernel.org>,
	 Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	 Jernej Skrabec <jernej.skrabec@gmail.com>,
	David Airlie <airlied@gmail.com>,
	 Daniel Vetter <daniel@ffwll.ch>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	 Thomas Zimmermann <tzimmermann@suse.de>,
	Rob Herring <robh@kernel.org>,
	 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	 Kishon Vijay Abraham I <kishon@kernel.org>,
	Shawn Guo <shawnguo@kernel.org>,
	 Sascha Hauer <s.hauer@pengutronix.de>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	 Fabio Estevam <festevam@gmail.com>,
	Sandor Yu <Sandor.yu@nxp.com>,
	dri-devel@lists.freedesktop.org,  devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-phy@lists.infradead.org,
	 imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	linux@ew.tq-group.com
Subject: Re: [PATCH v15 2/8] phy: Add HDMI configuration options
Date: Fri, 5 Apr 2024 18:09:48 +0300	[thread overview]
Message-ID: <7uculhmuov3z6o4xgv54ubdmju52y4jw7qkjbnslnyqbqgf5ku@sxrkuw4uwavx> (raw)
In-Reply-To: <ZhAJridEyhUeFVr0@matsya>

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@nxp.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@nxp.com>
> > > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> > > Acked-by: Vinod Koul <vkoul@kernel.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

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