Message-ID: <d9304ed0-911b-4877-a15c-981b3335bbf9@suse.de>
Date: Tue, 18 Feb 2025 11:09:29 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Aditya Garg <gargaditya08@...e.com>,
 "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
 "mripard@...nel.org" <mripard@...nel.org>,
 "airlied@...il.com" <airlied@...il.com>, "simona@...ll.ch" <simona@...ll.ch>
Cc: Kerem Karabay <kekrby@...il.com>, Atharva Tiwari <evepolonium@...il.com>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 2/2] drm/tiny: add driver for Apple Touch Bars in x86 Macs

Hi

Am 17.02.25 um 19:52 schrieb Aditya Garg:
> From: Kerem Karabay <kekrby@...il.com>
>
> The Touch Bars found on x86 Macs support two USB configurations: one
> where the device presents itself as a HID keyboard and can display
> predefined sets of keys, and one where the operating system has full
> control over what is displayed.
>
> This commit adds support for the display functionality of the second
> configuration. Functionality for the first configuration has been
> merged in the HID tree.
>
> Note that this driver has only been tested on T2 Macs, and only includes
> the USB device ID for these devices. Testing on T1 Macs would be
> appreciated.
>
> Credit goes to @imbushuo on GitHub for reverse engineering most of the
> protocol.
>
> Signed-off-by: Kerem Karabay <kekrby@...il.com>
> Co-developed-by: Atharva Tiwari <evepolonium@...il.com>
> Signed-off-by: Atharva Tiwari <evepolonium@...il.com>
> Co-developed-by: Aditya Garg <gargaditya08@...e.com>
> Signed-off-by: Aditya Garg <gargaditya08@...e.com>
> ---
>   drivers/gpu/drm/tiny/Kconfig      |  13 +
>   drivers/gpu/drm/tiny/Makefile     |   1 +
>   drivers/gpu/drm/tiny/appletbdrm.c | 702 ++++++++++++++++++++++++++++++

You also have to add the driver to MAINTAINERS.

>   3 files changed, 716 insertions(+)
>   create mode 100644 drivers/gpu/drm/tiny/appletbdrm.c
>
> diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> index 94cbdb133..76d1a2f9f 100644
> --- a/drivers/gpu/drm/tiny/Kconfig
> +++ b/drivers/gpu/drm/tiny/Kconfig
> @@ -1,5 +1,18 @@
>   # SPDX-License-Identifier: GPL-2.0-only
>   
> +config DRM_APPLETBDRM
> +	tristate "DRM support for Apple Touch Bars"
> +	depends on DRM && USB && MMU
> +	select DRM_GEM_SHMEM_HELPER
> +	select DRM_KMS_HELPER
> +	select HID_APPLETB_BL
> +	help
> +	  Say Y here if you want support for the display of Touch Bars on x86
> +	  MacBook Pros.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called appletbdrm.
> +
>   config DRM_ARCPGU
>   	tristate "ARC PGU"
>   	depends on DRM && OF
> diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
> index 60816d2eb..0a3a7837a 100644
> --- a/drivers/gpu/drm/tiny/Makefile
> +++ b/drivers/gpu/drm/tiny/Makefile
> @@ -1,5 +1,6 @@
>   # SPDX-License-Identifier: GPL-2.0-only
>   
> +obj-$(CONFIG_DRM_APPLETBDRM)		+= appletbdrm.o
>   obj-$(CONFIG_DRM_ARCPGU)		+= arcpgu.o
>   obj-$(CONFIG_DRM_BOCHS)			+= bochs.o
>   obj-$(CONFIG_DRM_CIRRUS_QEMU)		+= cirrus-qemu.o
> diff --git a/drivers/gpu/drm/tiny/appletbdrm.c b/drivers/gpu/drm/tiny/appletbdrm.c
> new file mode 100644
> index 000000000..f056f6280
> --- /dev/null
> +++ b/drivers/gpu/drm/tiny/appletbdrm.c
> @@ -0,0 +1,702 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Apple Touch Bar DRM Driver
> + *
> + * Copyright (c) 2023 Kerem Karabay <kekrby@...il.com>
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/module.h>
> +#include <linux/unaligned.h>
> +#include <linux/usb.h>
> +
> +#include <drm/drm_atomic.h>
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_crtc.h>
> +#include <drm/drm_damage_helper.h>
> +#include <drm/drm_drv.h>
> +#include <drm/drm_encoder.h>
> +#include <drm/drm_format_helper.h>
> +#include <drm/drm_fourcc.h>
> +#include <drm/drm_gem_atomic_helper.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +#include <drm/drm_gem_shmem_helper.h>
> +#include <drm/drm_plane.h>
> +#include <drm/drm_probe_helper.h>
> +
> +#define __APPLETBDRM_MSG_STR4(str4)	((__le32 __force)((str4[0] << 24) | (str4[1] << 16) | (str4[2] << 8) | str4[3]))
> +#define __APPLETBDRM_MSG_TOK4(tok4)	__APPLETBDRM_MSG_STR4(#tok4)
> +
> +#define APPLETBDRM_PIXEL_FORMAT		__APPLETBDRM_MSG_TOK4(RGBA) /* The actual format is BGR888 */
> +#define APPLETBDRM_BITS_PER_PIXEL	24
> +
> +#define APPLETBDRM_MSG_CLEAR_DISPLAY	__APPLETBDRM_MSG_TOK4(CLRD)
> +#define APPLETBDRM_MSG_GET_INFORMATION	__APPLETBDRM_MSG_TOK4(GINF)
> +#define APPLETBDRM_MSG_UPDATE_COMPLETE	__APPLETBDRM_MSG_TOK4(UDCL)
> +#define APPLETBDRM_MSG_SIGNAL_READINESS	__APPLETBDRM_MSG_TOK4(REDY)
> +
> +#define APPLETBDRM_BULK_MSG_TIMEOUT	1000
> +
> +#define drm_to_adev(_drm)		container_of(_drm, struct appletbdrm_device, drm)
> +#define adev_to_udev(adev)		interface_to_usbdev(to_usb_interface(adev->dev))
> +
> +struct appletbdrm_msg_request_header {
> +	__le16 unk_00;
> +	__le16 unk_02;
> +	__le32 unk_04;
> +	__le32 unk_08;
> +	__le32 size;
> +} __packed;
> +
> +struct appletbdrm_msg_response_header {
> +	u8 unk_00[16];
> +	__le32 msg;
> +} __packed;
> +
> +struct appletbdrm_msg_simple_request {
> +	struct appletbdrm_msg_request_header header;
> +	__le32 msg;
> +	u8 unk_14[8];
> +	__le32 size;
> +} __packed;
> +
> +struct appletbdrm_msg_information {
> +	struct appletbdrm_msg_response_header header;
> +	u8 unk_14[12];
> +	__le32 width;
> +	__le32 height;
> +	u8 bits_per_pixel;
> +	__le32 bytes_per_row;
> +	__le32 orientation;
> +	__le32 bitmap_info;
> +	__le32 pixel_format;
> +	__le32 width_inches;	/* floating point */
> +	__le32 height_inches;	/* floating point */
> +} __packed;
> +
> +struct appletbdrm_frame {
> +	__le16 begin_x;
> +	__le16 begin_y;
> +	__le16 width;
> +	__le16 height;
> +	__le32 buf_size;
> +	u8 buf[];
> +} __packed;
> +
> +struct appletbdrm_fb_request_footer {
> +	u8 unk_00[12];
> +	__le32 unk_0c;
> +	u8 unk_10[12];
> +	__le32 unk_1c;
> +	__le64 timestamp;
> +	u8 unk_28[12];
> +	__le32 unk_34;
> +	u8 unk_38[20];
> +	__le32 unk_4c;
> +} __packed;
> +
> +struct appletbdrm_fb_request {
> +	struct appletbdrm_msg_request_header header;
> +	__le16 unk_10;
> +	u8 msg_id;
> +	u8 unk_13[29];
> +	/*
> +	 * Contents of `data`:
> +	 * - struct appletbdrm_frame frames[];
> +	 * - struct appletbdrm_fb_request_footer footer;
> +	 * - padding to make the total size a multiple of 16
> +	 */
> +	u8 data[];
> +} __packed;
> +
> +struct appletbdrm_fb_request_response {
> +	struct appletbdrm_msg_response_header header;
> +	u8 unk_14[12];
> +	__le64 timestamp;
> +} __packed;
> +
> +struct appletbdrm_device {
> +	struct device *dev;
> +
> +	unsigned int in_ep;
> +	unsigned int out_ep;
> +
> +	unsigned int width;
> +	unsigned int height;
> +
> +	struct drm_device drm;
> +	struct drm_display_mode mode;
> +	struct drm_connector connector;
> +	struct drm_plane primary_plane;
> +	struct drm_crtc crtc;
> +	struct drm_encoder encoder;
> +};
> +
> +static int appletbdrm_send_request(struct appletbdrm_device *adev,
> +				   struct appletbdrm_msg_request_header *request, size_t size)
> +{
> +	struct usb_device *udev = adev_to_udev(adev);
> +	struct drm_device *drm = &adev->drm;
> +	int ret, actual_size;
> +
> +	ret = usb_bulk_msg(udev, usb_sndbulkpipe(udev, adev->out_ep),
> +			   request, size, &actual_size, APPLETBDRM_BULK_MSG_TIMEOUT);
> +	if (ret) {
> +		drm_err(drm, "Failed to send message (%d)\n", ret);
> +		return ret;
> +	}
> +
> +	if (actual_size != size) {
> +		drm_err(drm, "Actual size (%d) doesn't match expected size (%lu)\n",
> +			actual_size, size);
> +		return -EIO;
> +	}
> +
> +	return ret;
> +}
> +
> +static int appletbdrm_read_response(struct appletbdrm_device *adev,
> +				    struct appletbdrm_msg_response_header *response,
> +				    size_t size, u32 expected_response)
> +{
> +	struct usb_device *udev = adev_to_udev(adev);
> +	struct drm_device *drm = &adev->drm;
> +	int ret, actual_size;
> +	bool readiness_signal_received = false;
> +
> +retry:
> +	ret = usb_bulk_msg(udev, usb_rcvbulkpipe(udev, adev->in_ep),
> +			   response, size, &actual_size, APPLETBDRM_BULK_MSG_TIMEOUT);
> +	if (ret) {
> +		drm_err(drm, "Failed to read response (%d)\n", ret);
> +		return ret;
> +	}
> +
> +	/*
> +	 * The device responds to the first request sent in a particular
> +	 * timeframe after the USB device configuration is set with a readiness
> +	 * signal, in which case the response should be read again
> +	 */
> +	if (response->msg == APPLETBDRM_MSG_SIGNAL_READINESS) {
> +		if (!readiness_signal_received) {
> +			readiness_signal_received = true;
> +			goto retry;
> +		}
> +
> +		drm_err(drm, "Encountered unexpected readiness signal\n");
> +		return -EIO;
> +	}
> +
> +	if (actual_size != size) {
> +		drm_err(drm, "Actual size (%d) doesn't match expected size (%lu)\n",
> +			actual_size, size);
> +		return -EIO;
> +	}
> +
> +	if (response->msg != expected_response) {
> +		drm_err(drm, "Unexpected response from device (expected %p4ch found %p4ch)\n",
> +			&expected_response, &response->msg);
> +		return -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +static int appletbdrm_send_msg(struct appletbdrm_device *adev, u32 msg)
> +{
> +	struct appletbdrm_msg_simple_request *request;
> +	int ret;
> +
> +	request = kzalloc(sizeof(*request), GFP_KERNEL);
> +	if (!request)
> +		return -ENOMEM;
> +
> +	request->header.unk_00 = cpu_to_le16(2);
> +	request->header.unk_02 = cpu_to_le16(0x1512);
> +	request->header.size = cpu_to_le32(sizeof(*request) - sizeof(request->header));
> +	request->msg = msg;
> +	request->size = request->header.size;
> +
> +	ret = appletbdrm_send_request(adev, &request->header, sizeof(*request));
> +
> +	kfree(request);

This is temporary data for the send operation and save to free here?

> +
> +	return ret;
> +}
> +
> +static int appletbdrm_clear_display(struct appletbdrm_device *adev)
> +{
> +	return appletbdrm_send_msg(adev, APPLETBDRM_MSG_CLEAR_DISPLAY);
> +}
> +
> +static int appletbdrm_signal_readiness(struct appletbdrm_device *adev)
> +{
> +	return appletbdrm_send_msg(adev, APPLETBDRM_MSG_SIGNAL_READINESS);
> +}
> +
> +static int appletbdrm_get_information(struct appletbdrm_device *adev)
> +{
> +	struct appletbdrm_msg_information *info;
> +	struct drm_device *drm = &adev->drm;
> +	u8 bits_per_pixel;
> +	u32 pixel_format;
> +	int ret;
> +
> +	info = kzalloc(sizeof(*info), GFP_KERNEL);
> +	if (!info)
> +		return -ENOMEM;
> +
> +	ret = appletbdrm_send_msg(adev, APPLETBDRM_MSG_GET_INFORMATION);
> +	if (ret)
> +		return ret;
> +
> +	ret = appletbdrm_read_response(adev, &info->header, sizeof(*info),
> +				       APPLETBDRM_MSG_GET_INFORMATION);
> +	if (ret)
> +		goto free_info;
> +
> +	bits_per_pixel = info->bits_per_pixel;
> +	pixel_format = get_unaligned(&info->pixel_format);
> +
> +	adev->width = get_unaligned_le32(&info->width);
> +	adev->height = get_unaligned_le32(&info->height);
> +
> +	if (bits_per_pixel != APPLETBDRM_BITS_PER_PIXEL) {
> +		drm_err(drm, "Encountered unexpected bits per pixel value (%d)\n", bits_per_pixel);
> +		ret = -EINVAL;
> +		goto free_info;
> +	}
> +
> +	if (pixel_format != APPLETBDRM_PIXEL_FORMAT) {
> +		drm_err(drm, "Encountered unknown pixel format (%p4ch)\n", &pixel_format);
> +		ret = -EINVAL;
> +		goto free_info;
> +	}
> +
> +free_info:
> +	kfree(info);
> +
> +	return ret;
> +}
> +
> +static u32 rect_size(struct drm_rect *rect)
> +{
> +	return drm_rect_width(rect) * drm_rect_height(rect) * (APPLETBDRM_BITS_PER_PIXEL / 8);
> +}
> +
> +static int appletbdrm_flush_damage(struct appletbdrm_device *adev,
> +				   struct drm_plane_state *old_state,
> +				   struct drm_plane_state *state)
> +{
> +	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(state);
> +	struct appletbdrm_fb_request_response *response;
> +	struct appletbdrm_fb_request_footer *footer;
> +	struct drm_atomic_helper_damage_iter iter;
> +	struct drm_framebuffer *fb = state->fb;
> +	struct appletbdrm_fb_request *request;
> +	struct drm_device *drm = &adev->drm;
> +	struct appletbdrm_frame *frame;
> +	u64 timestamp = ktime_get_ns();
> +	struct drm_rect damage;
> +	size_t frames_size = 0;
> +	size_t request_size;
> +	int ret;
> +
> +	drm_atomic_helper_damage_iter_init(&iter, old_state, state);
> +	drm_atomic_for_each_plane_damage(&iter, &damage) {
> +		frames_size += struct_size(frame, buf, rect_size(&damage));
> +	}
> +
> +	if (!frames_size)
> +		return 0;
> +
> +	request_size = ALIGN(sizeof(*request) + frames_size + sizeof(*footer), 16);
> +
> +	request = kzalloc(request_size, GFP_KERNEL);
> +	if (!request)
> +		return -ENOMEM;
> +
> +	response = kzalloc(sizeof(*response), GFP_KERNEL);
> +	if (!response) {
> +		ret = -ENOMEM;
> +		goto free_request;
> +	}

This code runs in the middle of the atomic update. It's then too late to 
do error handling. If these allocs fail, the display hardware will 
remain in undefined state.

It is much preferable to allocate this memory in the atomic_check. To do 
so, you need a plane-state structure. Allocate the memory for request 
and response in the plane's atomic-check helper. If that fails, you can 
return an error there. Store the pointers and the request size in your 
plane-state structure and fetch them here.  The memory should later be 
freed in the plane's destroy callback. For an example, see how the 
ssd130x driver treats a buffer for a similar use case at [1].

[1] 
https://elixir.bootlin.com/linux/v6.13.2/source/drivers/gpu/drm/solomon/ssd130x.c#L1136


> +
> +	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
> +	if (ret) {
> +		drm_err(drm, "Failed to start CPU framebuffer access (%d)\n", ret);
> +		goto free_response;
> +	}
> +
> +	request->header.unk_00 = cpu_to_le16(2);
> +	request->header.unk_02 = cpu_to_le16(0x12);
> +	request->header.unk_04 = cpu_to_le32(9);
> +	request->header.size = cpu_to_le32(request_size - sizeof(request->header));
> +	request->unk_10 = cpu_to_le16(1);
> +	request->msg_id = timestamp & 0xff;
> +
> +	frame = (struct appletbdrm_frame *)request->data;
> +
> +	drm_atomic_helper_damage_iter_init(&iter, old_state, state);
> +	drm_atomic_for_each_plane_damage(&iter, &damage) {
> +		struct iosys_map dst = IOSYS_MAP_INIT_VADDR(frame->buf);
> +		u32 buf_size = rect_size(&damage);
> +
> +		/*
> +		 * The coordinates need to be translated to the coordinate
> +		 * system the device expects, see the comment in
> +		 * appletbdrm_setup_mode_config
> +		 */
> +		frame->begin_x = cpu_to_le16(damage.y1);
> +		frame->begin_y = cpu_to_le16(adev->height - damage.x2);
> +		frame->width = cpu_to_le16(drm_rect_height(&damage));
> +		frame->height = cpu_to_le16(drm_rect_width(&damage));
> +		frame->buf_size = cpu_to_le32(buf_size);
> +
> +		ret = drm_fb_blit(&dst, NULL, DRM_FORMAT_BGR888,
> +				  &shadow_plane_state->data[0], fb, &damage, &shadow_plane_state->fmtcnv_state);

Can we void the use of drm_fb_blit()? Since you know all formats in 
advance, just do

switch (format)
case XRGB8888: drm_fb_xrgb888_to_bgr888() break default:
     drm_fb_memcpy() break }We use blit in simpledrm and ofdrm, where we 
don't know the formats and output buffers in advance. But it's really 
not so great in other drivers, I think.
> +		if (ret) {
> +			drm_err(drm, "Failed to copy damage clip (%d)\n", ret);
> +			goto end_fb_cpu_access;
> +		}
> +
> +		frame = (void *)frame + struct_size(frame, buf, buf_size);
> +	}
> +
> +	footer = (struct appletbdrm_fb_request_footer *)&request->data[frames_size];
> +
> +	footer->unk_0c = cpu_to_le32(0xfffe);
> +	footer->unk_1c = cpu_to_le32(0x80001);
> +	footer->unk_34 = cpu_to_le32(0x80002);
> +	footer->unk_4c = cpu_to_le32(0xffff);
> +	footer->timestamp = cpu_to_le64(timestamp);
> +
> +	ret = appletbdrm_send_request(adev, &request->header, request_size);
> +	if (ret)
> +		goto end_fb_cpu_access;
> +
> +	ret = appletbdrm_read_response(adev, &response->header, sizeof(*response),
> +				       APPLETBDRM_MSG_UPDATE_COMPLETE);
> +	if (ret)
> +		goto end_fb_cpu_access;
> +
> +	if (response->timestamp != footer->timestamp) {
> +		drm_err(drm, "Response timestamp (%llu) doesn't match request timestamp (%llu)\n",
> +			le64_to_cpu(response->timestamp), timestamp);
> +		goto end_fb_cpu_access;
> +	}
> +
> +end_fb_cpu_access:
> +	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
> +free_response:
> +	kfree(response);
> +free_request:
> +	kfree(request);
> +
> +	return ret;
> +}
> +
> +static int appletbdrm_connector_helper_get_modes(struct drm_connector *connector)
> +{
> +	struct appletbdrm_device *adev = drm_to_adev(connector->dev);
> +
> +	return drm_connector_helper_get_modes_fixed(connector, &adev->mode);
> +}
> +
> +static const u32 appletbdrm_primary_plane_formats[] = {
> +	DRM_FORMAT_BGR888,
> +	DRM_FORMAT_XRGB8888, /* emulated */
> +};
> +
> +static int appletbdrm_primary_plane_helper_atomic_check(struct drm_plane *plane,
> +						   struct drm_atomic_state *state)
> +{
> +	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state, plane);
> +	struct drm_crtc *new_crtc = new_plane_state->crtc;
> +	struct drm_crtc_state *new_crtc_state = NULL;
> +	int ret;
> +
> +	if (new_crtc)
> +		new_crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);
> +
> +	ret = drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
> +						  DRM_PLANE_NO_SCALING,
> +						  DRM_PLANE_NO_SCALING,
> +						  false, false);
> +	if (ret)
> +		return ret;
> +	else if (!new_plane_state->visible)
> +		return 0;
> +
> +	return 0;
> +}
> +
> +static void appletbdrm_primary_plane_helper_atomic_update(struct drm_plane *plane,
> +						     struct drm_atomic_state *old_state)
> +{
> +	struct appletbdrm_device *adev = drm_to_adev(plane->dev);
> +	struct drm_device *drm = plane->dev;
> +	struct drm_plane_state *plane_state = plane->state;
> +	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(old_state, plane);
> +	int idx;

plane_state->fb can be NULL if the plane's atomic_disable is not set. At 
a minimum you should check this first and return if so.

A better idea is to implement atomic_disable. You can try to move the 
code from appletbdrm_crtc_helper_atomic_disable() to the plane's atomic 
disable and remove the CRTC helper. That would put all drawing code into 
the plane. The CRTC is more about programming a display mode.
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	appletbdrm_flush_damage(adev, old_plane_state, plane_state);
> +
> +	drm_dev_exit(idx);
> +}
> +
> +static const struct drm_plane_helper_funcs appletbdrm_primary_plane_helper_funcs = {
> +	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
> +	.atomic_check = appletbdrm_primary_plane_helper_atomic_check,
> +	.atomic_update = appletbdrm_primary_plane_helper_atomic_update,
> +};
> +
> +static const struct drm_plane_funcs appletbdrm_primary_plane_funcs = {
> +	.update_plane = drm_atomic_helper_update_plane,
> +	.disable_plane = drm_atomic_helper_disable_plane,
> +	.destroy = drm_plane_cleanup,
> +	DRM_GEM_SHADOW_PLANE_FUNCS,
> +};
> +
> +static enum drm_mode_status appletbdrm_crtc_helper_mode_valid(struct drm_crtc *crtc,
> +							  const struct drm_display_mode *mode)
> +{
> +	struct appletbdrm_device *adev = drm_to_adev(crtc->dev);
> +
> +	return drm_crtc_helper_mode_valid_fixed(crtc, mode, &adev->mode);
> +}
> +
> +static void appletbdrm_crtc_helper_atomic_disable(struct drm_crtc *crtc,
> +					     struct drm_atomic_state *crtc_state)
> +{
> +	struct appletbdrm_device *adev = drm_to_adev(crtc->dev);
> +	int idx;
> +
> +	if (!drm_dev_enter(&adev->drm, &idx))
> +		return;
> +
> +	appletbdrm_clear_display(adev);
> +
> +	drm_dev_exit(idx);
> +}
> +
> +static const struct drm_mode_config_funcs appletbdrm_mode_config_funcs = {
> +	.fb_create = drm_gem_fb_create_with_dirty,
> +	.atomic_check = drm_atomic_helper_check,
> +	.atomic_commit = drm_atomic_helper_commit,
> +};
> +
> +static const struct drm_connector_funcs appletbdrm_connector_funcs = {
> +	.reset = drm_atomic_helper_connector_reset,
> +	.destroy = drm_connector_cleanup,
> +	.fill_modes = drm_helper_probe_single_connector_modes,
> +	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> +	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> +};
> +
> +static const struct drm_connector_helper_funcs appletbdrm_connector_helper_funcs = {
> +	.get_modes = appletbdrm_connector_helper_get_modes,
> +};
> +
> +static const struct drm_crtc_helper_funcs appletbdrm_crtc_helper_funcs = {
> +	.mode_valid = appletbdrm_crtc_helper_mode_valid,
> +	.atomic_disable = appletbdrm_crtc_helper_atomic_disable,
> +};
> +
> +static const struct drm_crtc_funcs appletbdrm_crtc_funcs = {
> +	.reset = drm_atomic_helper_crtc_reset,
> +	.destroy = drm_crtc_cleanup,
> +	.set_config = drm_atomic_helper_set_config,
> +	.page_flip = drm_atomic_helper_page_flip,
> +	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
> +};
> +
> +static const struct drm_encoder_funcs appletbdrm_encoder_funcs = {
> +	.destroy = drm_encoder_cleanup,
> +};
> +
> +DEFINE_DRM_GEM_FOPS(appletbdrm_drm_fops);
> +
> +static const struct drm_driver appletbdrm_drm_driver = {
> +	DRM_GEM_SHMEM_DRIVER_OPS,

For USB devices, we need special wiring to make PRIME work. The PRIME 
device must support DMA, but a USB device doesn't. So we pass the USB 
controller device instead. See [2] for what udl does and how it obtains 
dmadev.

[2] 
https://elixir.bootlin.com/linux/v6.14-rc3/source/drivers/gpu/drm/udl/udl_drv.c#L76

> +	.name			= "appletbdrm",
> +	.desc			= "Apple Touch Bar DRM Driver",
> +	.date			= "20230910",

The date field has been removed recently.

> +	.major			= 1,
> +	.minor			= 0,
> +	.driver_features	= DRIVER_MODESET | DRIVER_GEM | DRIVER_ATOMIC,
> +	.fops			= &appletbdrm_drm_fops,
> +};
> +
> +static int appletbdrm_setup_mode_config(struct appletbdrm_device *adev)
> +{
> +	struct drm_connector *connector = &adev->connector;
> +	struct drm_plane *primary_plane;
> +	struct drm_crtc *crtc;
> +	struct drm_encoder *encoder;
> +	struct drm_device *drm = &adev->drm;
> +	struct device *dev = adev->dev;
> +	int ret;
> +
> +	ret = drmm_mode_config_init(drm);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to initialize mode configuration\n");
> +
> +	primary_plane = &adev->primary_plane;
> +	ret = drm_universal_plane_init(drm, primary_plane, 0,
> +				       &appletbdrm_primary_plane_funcs,
> +				       appletbdrm_primary_plane_formats,
> +				       ARRAY_SIZE(appletbdrm_primary_plane_formats),
> +				       NULL,
> +				       DRM_PLANE_TYPE_PRIMARY, NULL);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to initialize universal plane object\n");
> +	drm_plane_helper_add(primary_plane, &appletbdrm_primary_plane_helper_funcs);
> +	drm_plane_enable_fb_damage_clips(primary_plane);
> +
> +	crtc = &adev->crtc;
> +	ret = drm_crtc_init_with_planes(drm, crtc, primary_plane, NULL,
> +					&appletbdrm_crtc_funcs, NULL);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to initialize CRTC object\n");
> +	drm_crtc_helper_add(crtc, &appletbdrm_crtc_helper_funcs);
> +
> +	encoder = &adev->encoder;
> +	ret = drm_encoder_init(drm, encoder, &appletbdrm_encoder_funcs,
> +			       DRM_MODE_ENCODER_DAC, NULL);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to initialize encoder\n");
> +	encoder->possible_crtcs = drm_crtc_mask(crtc);
> +
> +	/*
> +	 * The coordinate system used by the device is different from the
> +	 * coordinate system of the framebuffer in that the x and y axes are
> +	 * swapped, and that the y axis is inverted; so what the device reports
> +	 * as the height is actually the width of the framebuffer and vice
> +	 * versa
> +	 */
> +	drm->mode_config.min_width = 0;
> +	drm->mode_config.min_height = 0;

> +	drm->mode_config.max_width = max(adev->height, DRM_SHADOW_PLANE_MAX_WIDTH);
> +	drm->mode_config.max_height = max(adev->width, DRM_SHADOW_PLANE_MAX_HEIGHT);

This might not work correctly. To use those SHADOW_PLANE_MAX constants, 
you have to fixup the damage coordinates to account for changes to the 
plane coordinates. Simpledrm does that by intersecting damage with 
dst_clip. [3] You also have to put the result at the right place within 
the display.

[3] 
https://elixir.bootlin.com/linux/v6.14-rc3/source/drivers/gpu/drm/tiny/simpledrm.c#L646

> +	drm->mode_config.preferred_depth = APPLETBDRM_BITS_PER_PIXEL;
> +	drm->mode_config.funcs = &appletbdrm_mode_config_funcs;
> +
> +	adev->mode = (struct drm_display_mode) {
> +		DRM_MODE_INIT(60, adev->height, adev->width,
> +			      DRM_MODE_RES_MM(adev->height, 218),
> +			      DRM_MODE_RES_MM(adev->width, 218))
> +	};
> +
> +	ret = drm_connector_init(drm, connector,
> +				 &appletbdrm_connector_funcs, DRM_MODE_CONNECTOR_USB);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to initialize connector\n");
> +
> +	drm_connector_helper_add(connector, &appletbdrm_connector_helper_funcs);
> +
> +	ret = drm_connector_set_panel_orientation(connector,
> +						  DRM_MODE_PANEL_ORIENTATION_RIGHT_UP);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to set panel orientation\n");
> +
> +	connector->display_info.non_desktop = true;
> +	ret = drm_object_property_set_value(&connector->base,
> +					    drm->mode_config.non_desktop_property, true);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to set non-desktop property\n");
> +
> +	ret = drm_connector_attach_encoder(connector, encoder);
> +
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to initialize simple display pipe\n");
> +
> +	drm_mode_config_reset(drm);
> +


> +	ret = drm_dev_register(drm, 0);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to register DRM device\n");

This call does not belong to the mode-setting pipeline and belongs into 
appletbdrm_probe().

> +
> +	return 0;
> +}
> +
> +static int appletbdrm_probe(struct usb_interface *intf,
> +			    const struct usb_device_id *id)
> +{
> +	struct usb_endpoint_descriptor *bulk_in, *bulk_out;
> +	struct device *dev = &intf->dev;
> +	struct appletbdrm_device *adev;
> +	int ret;
> +
> +	ret = usb_find_common_endpoints(intf->cur_altsetting, &bulk_in, &bulk_out, NULL, NULL);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to find bulk endpoints\n");
> +
> +	adev = devm_drm_dev_alloc(dev, &appletbdrm_drm_driver, struct appletbdrm_device, drm);
> +	if (IS_ERR(adev))
> +		return PTR_ERR(adev);
> +
> +	adev->dev = dev;
> +	adev->in_ep = bulk_in->bEndpointAddress;
> +	adev->out_ep = bulk_out->bEndpointAddress;
> +
> +	usb_set_intfdata(intf, adev);

Rather set the DRM device here and fetch it in the callbacks below. At 
some point, we might be able to share some of those helpers among drivers.

> +
> +	ret = appletbdrm_get_information(adev);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to get display information\n");
> +
> +	ret = appletbdrm_signal_readiness(adev);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to signal readiness\n");
> +

> +	ret = appletbdrm_clear_display(adev);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to clear display\n");

Clearing the display is not something usually done in probe. But I guess 
there's no better place. I'd do this as the final call in probe; after 
registering the device.  That way, it acts a bit like an in-kernel DRM 
client.

Best regards
Thomas

> +
> +	return appletbdrm_setup_mode_config(adev);
> +}
> +
> +static void appletbdrm_disconnect(struct usb_interface *intf)
> +{
> +	struct appletbdrm_device *adev = usb_get_intfdata(intf);
> +	struct drm_device *drm = &adev->drm;
> +
> +	drm_dev_unplug(drm);
> +	drm_atomic_helper_shutdown(drm);
> +}
> +
> +static void appletbdrm_shutdown(struct usb_interface *intf)
> +{
> +	struct appletbdrm_device *adev = usb_get_intfdata(intf);
> +
> +	/*
> +	 * The framebuffer needs to be cleared on shutdown since its content
> +	 * persists across boots
> +	 */
> +	drm_atomic_helper_shutdown(&adev->drm);
> +}
> +
> +static const struct usb_device_id appletbdrm_usb_id_table[] = {
> +	{ USB_DEVICE_INTERFACE_CLASS(0x05ac, 0x8302, USB_CLASS_AUDIO_VIDEO) },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(usb, appletbdrm_usb_id_table);
> +
> +static struct usb_driver appletbdrm_usb_driver = {
> +	.name		= "appletbdrm",
> +	.probe		= appletbdrm_probe,
> +	.disconnect	= appletbdrm_disconnect,
> +	.shutdown	= appletbdrm_shutdown,
> +	.id_table	= appletbdrm_usb_id_table,
> +};
> +module_usb_driver(appletbdrm_usb_driver);
> +
> +MODULE_AUTHOR("Kerem Karabay <kekrby@...il.com>");
> +MODULE_DESCRIPTION("Apple Touch Bar DRM Driver");
> +MODULE_LICENSE("GPL");

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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