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Message-ID: <1619db59285c707c60e3738c4fc287ebb7a6487a.camel@nxp.com>
Date: Thu, 01 Apr 2021 16:36:37 +0800
From: Liu Ying <victor.liu@....com>
To: Kishon Vijay Abraham I <kishon@...com>,
linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
dri-devel@...ts.freedesktop.org,
linux-arm-kernel@...ts.infradead.org
Cc: vkoul@...nel.org, robh+dt@...nel.org, a.hajda@...sung.com,
narmstrong@...libre.com, Laurent.pinchart@...asonboard.com,
jonas@...boo.se, jernej.skrabec@...l.net, airlied@...ux.ie,
daniel@...ll.ch, shawnguo@...nel.org, s.hauer@...gutronix.de,
kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
agx@...xcpu.org, robert.chiras@....com, martin.kepplinger@...i.sm,
robert.foss@...aro.org
Subject: Re: [PATCH v5 2/5] phy: Add LVDS configuration options
Hi Kishon,
First of all, thanks for your review.
On Wed, 2021-03-31 at 19:02 +0530, Kishon Vijay Abraham I wrote:
> Hi,
>
> On 25/03/21 2:30 pm, Liu Ying wrote:
> > This patch allows LVDS PHYs to be configured through
> > the generic functions and through a custom structure
> > added to the generic union.
> >
> > The parameters added here are based on common LVDS PHY
> > implementation practices. The set of parameters
> > should cover all potential users.
> >
> > Cc: Kishon Vijay Abraham I <kishon@...com>
> > Cc: Vinod Koul <vkoul@...nel.org>
> > Cc: NXP Linux Team <linux-imx@....com>
> > Signed-off-by: Liu Ying <victor.liu@....com>
> > ---
> > v4->v5:
> > * Align kernel-doc style to include/linux/phy/phy.h. (Vinod)
> > * Trivial tweaks.
> > * Drop Robert's R-b tag.
> >
> > v3->v4:
> > * Add Robert's R-b tag.
> >
> > v2->v3:
> > * No change.
> >
> > v1->v2:
> > * No change.
> >
> > include/linux/phy/phy-lvds.h | 32 ++++++++++++++++++++++++++++++++
> > include/linux/phy/phy.h | 4 ++++
> > 2 files changed, 36 insertions(+)
> > create mode 100644 include/linux/phy/phy-lvds.h
> >
> > diff --git a/include/linux/phy/phy-lvds.h b/include/linux/phy/phy-lvds.h
> > new file mode 100644
> > index 00000000..7a2f474
> > --- /dev/null
> > +++ b/include/linux/phy/phy-lvds.h
> > @@ -0,0 +1,32 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright 2020 NXP
> > + */
> > +
> > +#ifndef __PHY_LVDS_H_
> > +#define __PHY_LVDS_H_
> > +
> > +/**
> > + * struct phy_configure_opts_lvds - LVDS configuration set
> > + * @bits_per_lane_and_dclk_cycle: Number of bits per data lane and
> > + * differential clock cycle.
>
> phy_set_bus_width() instead?
This member aims to configure the number of bits transmitted during a
period of time(a clock cycle). It doesn't sound like a concept of 'bus
width'?
> > + * @differential_clk_rate: Clock rate, in Hertz, of the LVDS
> > + * differential clock.
>
> Please use clk API's to get rate.
I like your idea. But, this rate is likely runtime-configurable, e.g.,
a LVDS to HDMI chip is connected. It seems that there is no appropriate
driver to set the rate by calling clk_set_rate() then?
> > + * @lanes: Number of active, consecutive,
> > + * data lanes, starting from lane 0,
> > + * used for the transmissions.
> > + * @is_slave: Boolean, true if the phy is a slave
> > + * which works together with a master
> > + * phy to support dual link transmission,
> > + * otherwise a regular phy or a master phy.
>
> For parameters that are known at design time, it doesn't have to be
> passed from consumer driver. So all these parameters do they really have
> to be passed at runtime?
Yes for all, perhaps. Details below:
1) bits_per_lane_and_dclk_cycle
i.MX8qxp LVDS phy can only do 7, while i.MX8qm LVDS phy(a different IP)
can do either 7 or 10(configurable by setting a phy register).
2) differential_clk_rate
It's likely runtime-configurable, as I mentioned above.
3) lanes
The higher color depth is, the more lanes are used:
RGB666 - 3 lanes
RGB888 - 4 lanes
RGB101010 - 5 lanes
That means a phy with 5 lanes(like i.MX8qm LVDS phy) support up to the
3 types of RGB pixels.
Though the i.MX LVDS phys don't have any register to configure the
lanes to be used, it would be good to define it for phy_validate() or
other potential phys?
4) is_slave
Any i.MX8qxp LVDS phy instance can act as a regular phy or a master phy
or a slave phy. Changing mode at runtime is probably unneeded. But,
it's difficult for the phy driver to get the mode from device tree(see
drm_of_lvds_get_port_pixels_type()), I think. Export an i.MX8qxp LVDS
phy specific function to set this instead?
Regards,
Liu Ying
>
> Thanks
> Kishon
> > + *
> > + * This structure is used to represent the configuration state of a LVDS phy.
> > + */
> > +struct phy_configure_opts_lvds {
> > + unsigned int bits_per_lane_and_dclk_cycle;
> > + unsigned long differential_clk_rate;
> > + unsigned int lanes;
> > + bool is_slave;
> > +};
> > +
> > +#endif /* __PHY_LVDS_H_ */
> > diff --git a/include/linux/phy/phy.h b/include/linux/phy/phy.h
> > index e435bdb..d450b44 100644
> > --- a/include/linux/phy/phy.h
> > +++ b/include/linux/phy/phy.h
> > @@ -17,6 +17,7 @@
> > #include <linux/regulator/consumer.h>
> >
> > #include <linux/phy/phy-dp.h>
> > +#include <linux/phy/phy-lvds.h>
> > #include <linux/phy/phy-mipi-dphy.h>
> >
> > struct phy;
> > @@ -51,10 +52,13 @@ enum phy_mode {
> > * the MIPI_DPHY phy mode.
> > * @dp: Configuration set applicable for phys supporting
> > * the DisplayPort protocol.
> > + * @lvds: Configuration set applicable for phys supporting
> > + * the LVDS phy mode.
> > */
> > union phy_configure_opts {
> > struct phy_configure_opts_mipi_dphy mipi_dphy;
> > struct phy_configure_opts_dp dp;
> > + struct phy_configure_opts_lvds lvds;
> > };
> >
> > /**
> >
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