Re: [RFC PATCH 2/2] drm: xlnx: driver for Xilinx DSI TX Subsystem

[Hyun Kwon]

Hi Laurent,

On Sat, 2020-05-23 at 20:08:13 -0700, Laurent Pinchart wrote:
> Hi GVRao,
> 
> Thank you for the patch.
> 
> On Mon, May 04, 2020 at 11:43:48AM -0700, Hyun Kwon wrote:
> > On Mon, 2020-04-20 at 14:20:56 -0700, Venkateshwar Rao Gannavarapu wrote:
> > > The Xilinx MIPI DSI Tx Subsystem soft IP is used to display video
> > > data from AXI-4 stream interface.
> > > 
> > > It supports upto 4 lanes, optional register interface for the DPHY,
> > 
> > I don't see the register interface for dphy support.
> 
> I think the D-PHY should be supported through a PHY driver, as it seems
> to be shared between different subsystems.
> 

Right, if the logic is shared across subsystems. I can't tell if that's
the case as the IP comes as a single block. Maybe GVRao can confirm.

> > > multiple RGB color formats, command mode and video mode.
> > > This is a MIPI-DSI host driver and provides DSI bus for panels.
> > > This driver also helps to communicate with its panel using panel
> > > framework.
> > > 
> > > Signed-off-by: Venkateshwar Rao Gannavarapu <venkateshwar.rao.gannavarapu@xxxxxxxxxx>
> > > ---
> > >  drivers/gpu/drm/xlnx/Kconfig    |  11 +
> > >  drivers/gpu/drm/xlnx/Makefile   |   2 +
> > >  drivers/gpu/drm/xlnx/xlnx_dsi.c | 755 ++++++++++++++++++++++++++++++++++++++++
> 
> Daniel Vetter has recently expressed his opiion that bridge drivers
> should go to drivers/gpu/drm/bridge/. It would then be
> drivers/gpu/drm/bridge/xlnx/. I don't have a strong opinion myself.
> 
> > >  3 files changed, 768 insertions(+)
> > >  create mode 100644 drivers/gpu/drm/xlnx/xlnx_dsi.c
> > > 
> > > diff --git a/drivers/gpu/drm/xlnx/Kconfig b/drivers/gpu/drm/xlnx/Kconfig
> > > index aa6cd88..73873cf 100644
> > > --- a/drivers/gpu/drm/xlnx/Kconfig
> > > +++ b/drivers/gpu/drm/xlnx/Kconfig
> > > @@ -11,3 +11,14 @@ config DRM_ZYNQMP_DPSUB
> > >  	  This is a DRM/KMS driver for ZynqMP DisplayPort controller. Choose
> > >  	  this option if you have a Xilinx ZynqMP SoC with DisplayPort
> > >  	  subsystem.
> > > +
> > > +config DRM_XLNX_DSI
> > > +        tristate "Xilinx DRM DSI Subsystem Driver"
> > > +        select DRM_MIPI_DSI
> > > +        select DRM_PANEL
> > > +        select DRM_PANEL_SIMPLE
> > > +        help
> > > +	  This enables support for Xilinx MIPI-DSI.
> > 
> > This sentence is not needed with below. Could you please rephrase the whole?
> > 
> > > +	  This is a DRM/KMS driver for Xilinx programmable DSI controller.
> > > +	  Choose this option if you have a Xilinx MIPI DSI-TX controller
> > > +	  subsytem.
> > 
> > These seem incorrectly indented.
> > 
> > > diff --git a/drivers/gpu/drm/xlnx/Makefile b/drivers/gpu/drm/xlnx/Makefile
> > > index 2b844c6..b7ee6ef 100644
> > > --- a/drivers/gpu/drm/xlnx/Makefile
> > > +++ b/drivers/gpu/drm/xlnx/Makefile
> > > @@ -1,2 +1,4 @@
> > >  zynqmp-dpsub-objs += zynqmp_disp.o zynqmp_dpsub.o zynqmp_dp.o
> > >  obj-$(CONFIG_DRM_ZYNQMP_DPSUB) += zynqmp-dpsub.o
> > > +
> > > +obj-$(CONFIG_DRM_XLNX_DSI) += xlnx_dsi.o
> > > diff --git a/drivers/gpu/drm/xlnx/xlnx_dsi.c b/drivers/gpu/drm/xlnx/xlnx_dsi.c
> > > new file mode 100644
> > > index 0000000..b8cae59
> > > --- /dev/null
> > > +++ b/drivers/gpu/drm/xlnx/xlnx_dsi.c
> > > @@ -0,0 +1,755 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * Xilinx FPGA MIPI DSI Tx Controller driver
> > > + *
> > > + * Copyright (C) 2017 - 2019 Xilinx, Inc.
> > > + *
> > > + * Authors:
> > > + * - Saurabh Sengar <saurabhs@xxxxxxxxxx>
> > > + * - Venkateshwar Rao Gannavarapu <venkateshwar.rao.gannavarapu@xxxxxxxxxx>
> > > + */
> > > +
> > > +#include <drm/drm_atomic_helper.h>
> > > +#include <drm/drm_connector.h>
> > > +#include <drm/drm_crtc.h>
> > > +#include <drm/drm_crtc_helper.h>
> > > +#include <drm/drm_device.h>
> > > +#include <drm/drm_encoder.h>
> > > +#include <drm/drm_fourcc.h>
> > > +#include <drm/drm_gem_cma_helper.h>
> > > +#include <drm/drm_mipi_dsi.h>
> > > +#include <drm/drm_panel.h>
> > > +#include <drm/drm_probe_helper.h>
> > > +
> > > +#include <linux/clk.h>
> > > +#include <linux/component.h>
> > > +#include <linux/device.h>
> > > +#include <linux/iopoll.h>
> > > +#include <linux/of_device.h>
> > > +#include <linux/of_graph.h>
> > > +#include <linux/phy/phy.h>
> > > +
> > > +#include <video/mipi_display.h>
> > > +#include <video/videomode.h>
> > > +
> > > +/* DSI Tx IP registers */
> > > +#define XDSI_CCR			0x00
> > > +#define XDSI_CCR_COREENB		BIT(0)
> > > +#define XDSI_CCR_SOFTRST		BIT(1)
> > > +#define XDSI_CCR_CRREADY		BIT(2)
> > > +#define XDSI_CCR_CMDMODE		BIT(3)
> > > +#define XDSI_CCR_DFIFORST		BIT(4)
> > > +#define XDSI_CCR_CMDFIFORST		BIT(5)
> > > +#define XDSI_PCR			0x04

[snip]

> > > +	}
> > > +
> > > +	ret = clk_prepare_enable(dsi->video_aclk);
> > > +	if (ret) {
> > > +		dev_err(dev, "failed to enable video clk %d\n", ret);
> > > +		goto err_disable_dphy_clk;
> > > +	}
> > > +
> > > +	ret = component_add(dev, &xlnx_dsi_component_ops);
> 
> The driver should expose the DSI-TX as a drm_bridge instead of using the
> component framework. You shouldn't register a drm_encoder, and I don't
> think you should register a drm_connector either. Only bridge operations
> should be exposed, and the drm_bridge .attach() operation should return
> an error when DRM_BRIDGE_ATTACH_NO_CONNECTOR is not set. The top-level
> driver using this bridge should create the drm_encoder and
> drm_connector, most likely using drm_bridge_connector_init() to create
> the connector.
> 

Not clear to me if this has to be a bridge, and then what it will be attached
to. The IP block itself pretty much self-contains all functionalities already,
just like any other drm encoder / connector, so it doesn't have to be wrapped
around by any other layer. Please let me know your thought, so I can understand
better. :-)

Thanks,
-hyun