Re: [PATCH RFC 09/15] drm: imx: Add MIPI DSI host controller driver

[Thierry Reding]

On Wed, Dec 10, 2014 at 04:37:22PM +0800, Liu Ying wrote:
> This patch adds i.MX MIPI DSI host controller driver support.
> Currently, the driver supports the burst with sync pulses mode only.
> 
> Signed-off-by: Liu Ying <Ying.Liu@xxxxxxxxxxxxx>
> ---
>  .../devicetree/bindings/drm/imx/mipi_dsi.txt       |   81 ++
>  drivers/gpu/drm/imx/Kconfig                        |    6 +
>  drivers/gpu/drm/imx/Makefile                       |    1 +
>  drivers/gpu/drm/imx/imx-mipi-dsi.c                 | 1017 ++++++++++++++++++++
>  4 files changed, 1105 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/drm/imx/mipi_dsi.txt
>  create mode 100644 drivers/gpu/drm/imx/imx-mipi-dsi.c
> 
> diff --git a/Documentation/devicetree/bindings/drm/imx/mipi_dsi.txt b/Documentation/devicetree/bindings/drm/imx/mipi_dsi.txt
> new file mode 100644
> index 0000000..3d07fd7
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/drm/imx/mipi_dsi.txt
> @@ -0,0 +1,81 @@
> +Device-Tree bindings for MIPI DSI host controller
> +
> +MIPI DSI host controller
> +========================
> +
> +The MIPI DSI host controller is a Synopsys DesignWare IP.
> +It is a digital core that implements all protocol functions defined
> +in the MIPI DSI specification, providing an interface between the
> +system and the MIPI DPHY, and allowing communication with a MIPI DSI
> +compliant display.
> +
> +Required properties:
> + - #address-cells : Should be <1>.
> + - #size-cells : Should be <0>.
> + - compatible : Should be "fsl,imx6q-mipi-dsi" for i.MX6q/sdl SoCs.
> + - reg : Physical base address of the controller and length of memory
> +         mapped region.
> + - interrupts : The controller's interrupt number to the CPU(s).
> + - gpr : Should be <&gpr>.
> +         The phandle points to the iomuxc-gpr region containing the
> +         multiplexer control register for the controller.

Side-note: Shouldn't this really be a pinmux, then?

> + - clocks, clock-names : Phandles to the controller pllref, pllref_gate
> +           and core_cfg clocks, as described in [1] and [2].
> + - panel@0 : A panel node which contains a display-timings child node as
> +             defined in [3].

There's no need for these to be named panel@*. They could be bridges for
example. And no, they shouldn't contain a display-timings child node
either. Panels should have a proper driver and the driver being device
specific it should have the timings embedded.

> + - port@[0-4] : Up to four port nodes with endpoint definitions as defined
> +   in [4], corresponding to the four inputs to the controller multiplexer.
> +   Note that each port node should contain the input-port property to
> +   distinguish it from the panel node, as described in [5].

[4] says that you can group all port nodes under a ports parent node. I
think this is really what you want to do here to make it clear that the
ports aren't part of the DSI host binding part of the device.

> diff --git a/drivers/gpu/drm/imx/imx-mipi-dsi.c b/drivers/gpu/drm/imx/imx-mipi-dsi.c
[...]
> +/*
> + * i.MX drm driver - MIPI DSI Host Controller
> + *
> + * Copyright (C) 2011-2014 Freescale Semiconductor, Inc.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/component.h>
> +#include <linux/mfd/syscon.h>
> +#include <linux/mfd/syscon/imx6q-iomuxc-gpr.h>
> +#include <linux/module.h>
> +#include <linux/of_address.h>
> +#include <linux/of_device.h>
> +#include <linux/regmap.h>
> +#include <linux/videodev2.h>
> +#include <asm/div64.h>

Don't you want the more generic linux/math64.h here?

> +#include <drm/drmP.h>
> +#include <drm/drm_crtc_helper.h>
> +#include <drm/drm_fb_helper.h>

I don't see any of the functions defined in that header used here.

> +#include <drm/drm_mipi_dsi.h>
> +#include <drm/drm_panel.h>
> +#include <video/mipi_display.h>
> +#include <video/of_videomode.h>
> +#include <video/videomode.h>
> +
> +#include "imx-drm.h"
> +
> +#define DRIVER_NAME 			"imx-mipi-dsi"
> +
> +#define	DSI_VERSION			0x00
> +
> +#define	DSI_PWR_UP			0x04
> +#define	RESET				0
> +#define	POWERUP				BIT(0)
> +
> +#define	DSI_CLKMGR_CFG			0x08
> +#define TO_CLK_DIVIDSION(div)		(((div) & 0xff) << 8)
> +#define TX_ESC_CLK_DIVIDSION(div)	(((div) & 0xff) << 0)

Your indentation here is... weird.

> +#define IMX_MIPI_DSI_MAX_DATA_LANES	2
> +
> +#define PHY_STATUS_TIMEOUT		10
> +#define CMD_PKT_STATUS_TIMEOUT		20
> +
> +#define IMX_MIPI_DSI_PLD_DATA_BUF_SIZE	4
> +
> +#define MHZ				1000000

Why not reuse the existing USEC_PER_SEC?

> +#define host_to_dsi(host) container_of(host, struct imx_mipi_dsi, dsi_host)
> +#define con_to_dsi(x) container_of(x, struct imx_mipi_dsi, connector)
> +#define enc_to_dsi(x) container_of(x, struct imx_mipi_dsi, encoder)

These should really be static inline functions for proper type safety.

> +struct imx_mipi_dsi {
> +	struct mipi_dsi_host dsi_host;
> +	struct drm_connector connector;
> +	struct drm_encoder encoder;
> +	struct device_node *panel_node;
> +	struct drm_panel *panel;
> +	struct device *dev;
> +
> +	struct regmap *regmap;
> +	void __iomem *base;
> +
> +	struct clk *pllref_clk;
> +	struct clk *pllref_gate_clk;
> +	struct clk *cfg_clk;
> +
> +	unsigned int lane_mbps; /* per lane */
> +	u32 channel;
> +	u32 lanes;
> +	u32 format;
> +	struct videomode vm;
> +
> +	bool enabled;

Do you really need this flag?

> +};
> +
> +enum {
> +	STATUS_TO_CLEAR,
> +	STATUS_TO_SET,
> +};
> +
> +struct dphy_pll_testdin_map {
> +	int max_mbps;

unsigned?

> +	u8 testdin;
> +};
> +
> +/* The table is based on 27MHz DPHY pll reference clock. */
> +static const struct dphy_pll_testdin_map dptdin_map[] = {
> +	{160, 0x04}, {180, 0x24}, {200, 0x44}, {210, 0x06},
> +	{240, 0x26}, {250, 0x46}, {270, 0x08}, {300, 0x28},
> +	{330, 0x48}, {360, 0x2a}, {400, 0x4a}, {450, 0x0c},
> +	{500, 0x2c}, {550, 0x0e}, {600, 0x2e}, {650, 0x10},
> +	{700, 0x30}, {750, 0x12}, {800, 0x32}, {850, 0x14},
> +	{900, 0x34}, {950, 0x54}, {1000, 0x74}
> +};
> +
> +static int max_mbps_to_testdin(unsigned int max_mbps)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(dptdin_map); i++)
> +		if (dptdin_map[i].max_mbps == max_mbps)
> +			return dptdin_map[i].testdin;
> +
> +	return -EINVAL;
> +}
> +
> +static int format_to_bpp(struct imx_mipi_dsi *dsi)
> +{
> +	switch (dsi->format) {
> +	case MIPI_DSI_FMT_RGB888:
> +	case MIPI_DSI_FMT_RGB666:
> +		return 24;
> +	case MIPI_DSI_FMT_RGB666_PACKED:
> +		return 18;
> +	case MIPI_DSI_FMT_RGB565:
> +		return 16;
> +	default:
> +		dev_err(dsi->dev, "unsupported pixel format\n");
> +		return -EINVAL;
> +	}
> +}

Is there a reason why this can't be a standard MIPI DSI function?

> +
> +static int check_status(struct imx_mipi_dsi *dsi, u32 reg, u32 status,
> +			int timeout, bool to_set)
> +{
> +	u32 val;
> +	bool out = false;
> +
> +	val = dsi_read(dsi, reg);
> +	for (;;) {
> +		out = to_set ? (val & status) : !(val & status);
> +		if (out)
> +			break;
> +
> +		if (!timeout--)
> +			return -EFAULT;
> +
> +		msleep(1);
> +		val = dsi_read(dsi, reg);
> +	}
> +	return 0;
> +}

You should probably use a properly timed loop here. msleep() isn't
guaranteed to return after exactly one millisecond, so your timeout is
never going to be accurate. Something like the following would be better
in my opinion:

	timeout = jiffies + msecs_to_jiffies(timeout);

	while (time_before(jiffies, timeout)) {
		...
	}

Also timeout should be unsigned long in that case.

> +static int imx_mipi_dsi_host_attach(struct mipi_dsi_host *host,
> +				    struct mipi_dsi_device *device)
> +{
> +	struct imx_mipi_dsi *dsi = host_to_dsi(host);
> +	int ret;
> +
> +	if (device->lanes > IMX_MIPI_DSI_MAX_DATA_LANES) {
> +		dev_err(dsi->dev, "the number of data lanes(%d) is too many\n",
> +				device->lanes);
> +		return -EINVAL;
> +	}
> +
> +	if (!(device->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) ||
> +	    !(device->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE)) {
> +		dev_err(dsi->dev, "device mode is unsupported\n");
> +		return -EINVAL;
> +	}
> +
> +	dsi->lanes = device->lanes;
> +	dsi->channel = device->channel;
> +	dsi->format = device->format;
> +	dsi->panel_node = device->dev.of_node;
> +	of_get_videomode(dsi->panel_node, &dsi->vm, 0);

No, you shouldn't use this. Query the mode from the panel instead. Or
rather, encode this requirement in ->mode_valid() since that'll give you
direct access to the mode.

That way, ->host_attach() becomes a filter for compatible devices, yet
devices may support multiple modes, therefore ->mode_valid() can be used
to filter out those that don't work with your DSI host controller. There
is a subtle difference here between devices that are compatible with the
controller and modes that the controller doesn't support.

> +
> +	ret = imx_mipi_dsi_get_lane_bps(dsi, &dsi->lane_mbps);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int imx_mipi_dsi_host_detach(struct mipi_dsi_host *host,
> +				    struct mipi_dsi_device *device)
> +{
> +	struct imx_mipi_dsi *dsi = host_to_dsi(host);
> +
> +	dsi->panel_node = NULL;
> +	dsi->panel = NULL;
> +
> +	return 0;
> +}

You'll want to detach from the panel here as well.

> +
> +static int imx_mipi_dsi_gen_pkt_hdr_write(struct imx_mipi_dsi *dsi, u32 val)
> +{
> +	int ret;
> +
> +	ret = check_status(dsi, DSI_CMD_PKT_STATUS, GEN_CMD_FULL,
> +			   CMD_PKT_STATUS_TIMEOUT, STATUS_TO_CLEAR);
> +	if (ret < 0) {
> +		dev_err(dsi->dev, "failed to get avaliable command FIFO\n");
> +		return ret;
> +	}
> +
> +	dsi_write(dsi, DSI_GEN_HDR, val);
> +
> +	ret = check_status(dsi, DSI_CMD_PKT_STATUS,
> +			   GEN_CMD_EMPTY | GEN_PLD_W_EMPTY,
> +			   CMD_PKT_STATUS_TIMEOUT, STATUS_TO_SET);
> +	if (ret < 0) {
> +		dev_err(dsi->dev, "failed to write command FIFO\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static int imx_mipi_dsi_dcs_short_write(struct imx_mipi_dsi *dsi,
> +					const struct mipi_dsi_msg *msg)
> +{
> +	const u16 *tx_buf = msg->tx_buf;
> +	u32 val = GEN_HDATA(*tx_buf) | GEN_HTYPE(msg->type);
> +
> +	if (msg->tx_len > 2) {
> +		dev_err(dsi->dev, "too long tx buf length %d for short write\n",
> +			msg->tx_len);
> +		return -EINVAL;
> +	}
> +
> +	return imx_mipi_dsi_gen_pkt_hdr_write(dsi, val);
> +}

It seems like you would profit from converting to the newly introduced
mipi_dsi_create_packet() helper which does most of the packing along
with some sanity checking for you.

> +
> +static int imx_mipi_dsi_dcs_long_write(struct imx_mipi_dsi *dsi,
> +				       const struct mipi_dsi_msg *msg)
> +{
> +	const u32 *tx_buf = msg->tx_buf;
> +	int len = msg->tx_len, ret;
> +	u32 val = GEN_HDATA(msg->tx_len) | GEN_HTYPE(msg->type);
> +
> +	if (msg->tx_len < 3) {
> +		dev_err(dsi->dev, "wrong tx buf length %d for long write\n",
> +			msg->tx_len);
> +		return -EINVAL;
> +	}
> +
> +	/* write the bulks */
> +	while (len / IMX_MIPI_DSI_PLD_DATA_BUF_SIZE) {
> +		dsi_write(dsi, DSI_GEN_PLD_DATA, *tx_buf);
> +		tx_buf++;
> +		len -= IMX_MIPI_DSI_PLD_DATA_BUF_SIZE;

This is confusing. Maybe a better option would be to use sizeof(*tx_buf)
instead of this macro. You're effectively consuming one u32 with each
write, irrespective of what the value of the macro is.

> +		ret = check_status(dsi, DSI_CMD_PKT_STATUS, GEN_PLD_W_FULL,
> +				   CMD_PKT_STATUS_TIMEOUT, STATUS_TO_CLEAR);
> +		if (ret < 0) {
> +			dev_err(dsi->dev, "failed to get avaliable "
> +					"write payload FIFO\n");
> +			return ret;
> +		}
> +	}
> +
> +	/* write the remainder */
> +	if (len > 0) {
> +		ret = check_status(dsi, DSI_CMD_PKT_STATUS, GEN_PLD_W_FULL,
> +				   CMD_PKT_STATUS_TIMEOUT, STATUS_TO_CLEAR);
> +		if (ret < 0) {
> +			dev_err(dsi->dev, "failed to get avaliable "
> +					"write payload FIFO\n");
> +			return ret;
> +		}
> +		dsi_write(dsi, DSI_GEN_PLD_DATA, *tx_buf);
> +	}

This is really duplicating what the above loop does. Why can't you do it
in a single loop? Also the transmission buffer isn't guaranteed to be a
multiple of 4 bytes, so you could have the situation where len > 0 and
len < 4 and yet you'll be reading 4 bytes by doing *tx_buf and accessing
memory that you shouldn't.

> +	return imx_mipi_dsi_gen_pkt_hdr_write(dsi, val);
> +}
> +
> +static ssize_t imx_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
> +					  const struct mipi_dsi_msg *msg)
> +{
> +	struct imx_mipi_dsi *dsi = host_to_dsi(host);
> +	int ret;
> +
> +	switch (msg->type) {
> +	case MIPI_DSI_DCS_SHORT_WRITE:
> +	case MIPI_DSI_DCS_SHORT_WRITE_PARAM:
> +	case MIPI_DSI_SET_MAXIMUM_RETURN_PACKET_SIZE:
> +		ret = imx_mipi_dsi_dcs_short_write(dsi, msg);
> +		break;
> +	case MIPI_DSI_DCS_LONG_WRITE:
> +		ret = imx_mipi_dsi_dcs_long_write(dsi, msg);
> +		break;
> +	default:
> +		dev_err(dsi->dev, "unsupported message type\n");
> +		ret = -EFAULT;

EFAULT really isn't appropriate here.

> +	}
> +
> +	return ret;
> +}
> +
> +static const struct mipi_dsi_host_ops imx_mipi_dsi_host_ops = {
> +	.attach = imx_mipi_dsi_host_attach,
> +	.detach = imx_mipi_dsi_host_detach,
> +	.transfer = imx_mipi_dsi_host_transfer,
> +};
> +
> +static enum drm_connector_status
> +imx_mipi_dsi_detect(struct drm_connector *connector, bool force)
> +{
> +	struct imx_mipi_dsi *dsi = con_to_dsi(connector);
> +
> +	if (!dsi->panel) {
> +		dsi->panel = of_drm_find_panel(dsi->panel_node);
> +		if (dsi->panel)
> +			drm_panel_attach(dsi->panel, &dsi->connector);
> +	}
> +
> +	if (dsi->panel)
> +		return connector_status_connected;
> +
> +	return connector_status_disconnected;
> +
> +}

You really shouldn't be doing that here. of_drm_find_panel() returning
NULL should be considered cause for deferring probe. I suspect that the
driver doesn't really handle that very well at all, though, since if it
did you would've run into the same issue that Benjamin ran into this
morning.

> +static void imx_mipi_dsi_encoder_prepare(struct drm_encoder *encoder)
> +{
> +	struct imx_mipi_dsi *dsi = enc_to_dsi(encoder);
> +	u32 interface_pix_fmt;
> +
> +	switch (dsi->format) {
> +	case MIPI_DSI_FMT_RGB888:
> +		interface_pix_fmt = V4L2_PIX_FMT_RGB24;
> +		break;
> +	case MIPI_DSI_FMT_RGB565:
> +		interface_pix_fmt = V4L2_PIX_FMT_RGB565;
> +		break;
> +	default:
> +		dev_err(dsi->dev, "unsupported DSI pixel format\n");
> +		return;

Why even try doing this if you know upfront that it can't be done. You
know much earlier than this that you can't drive the pixel format, why
not abort then?

People are much more likely to notice that the panel isn't supported if
the DSI output doesn't even show up (or doesn't expose any modes) rather
than if they have to find this error message in dmesg.

> +static void imx_mipi_dsi_video_mode_config(struct imx_mipi_dsi *dsi)
> +{
> +	u32 val;
> +
> +	val = VID_MODE_TYPE_BURST_SYNC_PULSES | ENABLE_LOW_POWER;
> +
> +	dsi_write(dsi, DSI_VID_MODE_CFG, val);
> +}

You probably want to parameterize based on the DSI peripheral's flags. I
see that you do reject devices with any other modes, so this may not be
necessary now. Out of curiosity, the hardware supports other modes,
right?

[...]
> +MODULE_LICENSE("GPL v2");

Sigh... according to your header comment this needs to be "GPL".

Thierry

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