Re: [PATCH v3 0/3] drm: atmel-hlcdc: clut support

Boris Brezillon
2017-06-19T07:48:53Z

+Alexandre and Nicolas

Hi Peter,

Can you please Cc at91 maintainers next time?

On Mon, 19 Jun 2017 09:44:23 +0200
Peter Rosin <peda@axentia.se> wrote:

> Hi!
>
> This series adds support for an 8-bit clut mode in the atmel-hlcdc
> driver.
>
> I have now tested patch 1 with the below program (modeset.c
> adapted from https://github.com/dvdhrm/docs/tree/master/drm-howto
> to use an 8-bit mode).
>
> Since v2 I have also cleared up why the first 16 entries of the clut
> was not working right. It was of course my own damn fault, and the
> fix was in atmel_hlcdc_layer_write_clut function which called the
> ...write_reg function which in turn added an extra offset of 16
> registers...
>
> Changes since v2:
>
> - Fix mapping to the clut registers.
>
> Changes since v1:
>
> - Move the clut update from atmel_hlcdc_crtc_mode_valid to
> atmel_hlcdc_plane_atomic_update.
> - Add default .gamma_set helper (drm_atomic_helper_legacy_gamma_set).
> - Don't keep a spare copy of the clut, reuse gamma_store instead.
> - Don't try to synchronize the legacy fb clut with the drm clut.
>
> As I said in v2, I have not added any .clut_offset to the overlay2
> layer of sama5d4, since the chip does not appear to have that layer.
> I didn't do that to make it easier to work with the patch previously
> sent to remove that layer, but I suspect bad things may happen to
> sama5d4 users if they do not have that layer removed.
>
> Cheers,
> peda
>
> modeset-pal.c (didn't update any comments, sorry)
> ----------------8<---------------
> /*
> * modeset - DRM Modesetting Example
> *
> * Written 2012 by David Herrmann <dh.herrmann@googlemail.com>
> * Dedicated to the Public Domain.
> */
>
> /*
> * DRM Modesetting Howto
> * This document describes the DRM modesetting API. Before we can use the DRM
> * API, we have to include xf86drm.h and xf86drmMode.h. Both are provided by
> * libdrm which every major distribution ships by default. It has no other
> * dependencies and is pretty small.
> *
> * Please ignore all forward-declarations of functions which are used later. I
> * reordered the functions so you can read this document from top to bottom. If
> * you reimplement it, you would probably reorder the functions to avoid all the
> * nasty forward declarations.
> *
> * For easier reading, we ignore all memory-allocation errors of malloc() and
> * friends here. However, we try to correctly handle all other kinds of errors
> * that may occur.
> *
> * All functions and global variables are prefixed with "modeset_*" in this
> * file. So it should be clear whether a function is a local helper or if it is
> * provided by some external library.
> */
>
> #define _GNU_SOURCE
> #include <errno.h>
> #include <fcntl.h>
> #include <stdbool.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/mman.h>
> #include <time.h>
> #include <unistd.h>
> #include <xf86drm.h>
> #include <xf86drmMode.h>
>
> struct modeset_dev;
> static int modeset_find_crtc(int fd, drmModeRes *res, drmModeConnector *conn,
> struct modeset_dev *dev);
> static int modeset_create_fb(int fd, struct modeset_dev *dev);
> static int modeset_setup_dev(int fd, drmModeRes *res, drmModeConnector *conn,
> struct modeset_dev *dev);
> static int modeset_open(int *out, const char *node);
> static int modeset_prepare(int fd);
> static void modeset_draw(int fd);
> static void modeset_cleanup(int fd);
>
> /*
> * When the linux kernel detects a graphics-card on your machine, it loads the
> * correct device driver (located in kernel-tree at ./drivers/gpu/drm/<xy>) and
> * provides two character-devices to control it. Udev (or whatever hotplugging
> * application you use) will create them as:
> * /dev/dri/card0
> * /dev/dri/controlID64
> * We only need the first one. You can hard-code this path into your application
> * like we do here, but it is recommended to use libudev with real hotplugging
> * and multi-seat support. However, this is beyond the scope of this document.
> * Also note that if you have multiple graphics-cards, there may also be
> * /dev/dri/card1, /dev/dri/card2, ...
> *
> * We simply use /dev/dri/card0 here but the user can specify another path on
> * the command line.
> *
> * modeset_open(out, node): This small helper function opens the DRM device
> * which is given as @node. The new fd is stored in @out on success. On failure,
> * a negative error code is returned.
> * After opening the file, we also check for the DRM_CAP_DUMB_BUFFER capability.
> * If the driver supports this capability, we can create simple memory-mapped
> * buffers without any driver-dependent code. As we want to avoid any radeon,
> * nvidia, intel, etc. specific code, we depend on DUMB_BUFFERs here.
> */
>
> static int modeset_open(int *out, const char *node)
> {
> int fd, ret;
> uint64_t has_dumb;
>
> fd = open(node, O_RDWR | O_CLOEXEC);
> if (fd < 0) {
> ret = -errno;
> fprintf(stderr, "cannot open '%s': %m\n", node);
> return ret;
> }
>
> if (drmGetCap(fd, DRM_CAP_DUMB_BUFFER, &has_dumb) < 0 ||
> !has_dumb) {
> fprintf(stderr, "drm device '%s' does not support dumb buffers\n",
> node);
> close(fd);
> return -EOPNOTSUPP;
> }
>
> *out = fd;
> return 0;
> }
>
> /*
> * As a next step we need to find our available display devices. libdrm provides
> * a drmModeRes structure that contains all the needed information. We can
> * retrieve it via drmModeGetResources(fd) and free it via
> * drmModeFreeResources(res) again.
> *
> * A physical connector on your graphics card is called a "connector". You can
> * plug a monitor into it and control what is displayed. We are definitely
> * interested in what connectors are currently used, so we simply iterate
> * through the list of connectors and try to display a test-picture on each
> * available monitor.
> * However, this isn't as easy as it sounds. First, we need to check whether the
> * connector is actually used (a monitor is plugged in and turned on). Then we
> * need to find a CRTC that can control this connector. CRTCs are described
> * later on. After that we create a framebuffer object. If we have all this, we
> * can mmap() the framebuffer and draw a test-picture into it. Then we can tell
> * the DRM device to show the framebuffer on the given CRTC with the selected
> * connector.
> *
> * As we want to draw moving pictures on the framebuffer, we actually have to
> * remember all these settings. Therefore, we create one "struct modeset_dev"
> * object for each connector+crtc+framebuffer pair that we successfully
> * initialized and push it into the global device-list.
> *
> * Each field of this structure is described when it is first used. But as a
> * summary:
> * "struct modeset_dev" contains: {
> * - @next: points to the next device in the single-linked list
> *
> * - @width: width of our buffer object
> * - @height: height of our buffer object
> * - @stride: stride value of our buffer object
> * - @size: size of the memory mapped buffer
> * - @handle: a DRM handle to the buffer object that we can draw into
> * - @map: pointer to the memory mapped buffer
> *
> * - @mode: the display mode that we want to use
> * - @fb: a framebuffer handle with our buffer object as scanout buffer
> * - @conn: the connector ID that we want to use with this buffer
> * - @crtc: the crtc ID that we want to use with this connector
> * - @saved_crtc: the configuration of the crtc before we changed it. We use it
> * so we can restore the same mode when we exit.
> * }
> */
>
> struct modeset_dev {
> struct modeset_dev *next;
>
> uint32_t width;
> uint32_t height;
> uint32_t stride;
> uint32_t size;
> uint32_t handle;
> uint8_t *map;
>
> drmModeModeInfo mode;
> uint32_t fb;
> uint32_t conn;
> uint32_t crtc;
> drmModeCrtc *saved_crtc;
> };
>
> static struct modeset_dev *modeset_list = NULL;
>
> /*
> * So as next step we need to actually prepare all connectors that we find. We
> * do this in this little helper function:
> *
> * modeset_prepare(fd): This helper function takes the DRM fd as argument and
> * then simply retrieves the resource-info from the device. It then iterates
> * through all connectors and calls other helper functions to initialize this
> * connector (described later on).
> * If the initialization was successful, we simply add this object as new device
> * into the global modeset device list.
> *
> * The resource-structure contains a list of all connector-IDs. We use the
> * helper function drmModeGetConnector() to retrieve more information on each
> * connector. After we are done with it, we free it again with
> * drmModeFreeConnector().
> * Our helper modeset_setup_dev() returns -ENOENT if the connector is currently
> * unused and no monitor is plugged in. So we can ignore this connector.
> */
>
> static int modeset_prepare(int fd)
> {
> drmModeRes *res;
> drmModeConnector *conn;
> unsigned int i;
> struct modeset_dev *dev;
> int ret;
>
> /* retrieve resources */
> res = drmModeGetResources(fd);
> if (!res) {
> fprintf(stderr, "cannot retrieve DRM resources (%d): %m\n",
> errno);
> return -errno;
> }
>
> /* iterate all connectors */
> for (i = 0; i < res->count_connectors; ++i) {
> /* get information for each connector */
> conn = drmModeGetConnector(fd, res->connectors[i]);
> if (!conn) {
> fprintf(stderr, "cannot retrieve DRM connector %u:%u (%d): %m\n",
> i, res->connectors[i], errno);
> continue;
> }
>
> /* create a device structure */
> dev = malloc(sizeof(*dev));
> memset(dev, 0, sizeof(*dev));
> dev->conn = conn->connector_id;
>
> /* call helper function to prepare this connector */
> ret = modeset_setup_dev(fd, res, conn, dev);
> if (ret) {
> if (ret != -ENOENT) {
> errno = -ret;
> fprintf(stderr, "cannot setup device for connector %u:%u (%d): %m\n",
> i, res->connectors[i], errno);
> }
> free(dev);
> drmModeFreeConnector(conn);
> continue;
> }
>
> /* free connector data and link device into global list */
> drmModeFreeConnector(conn);
> dev->next = modeset_list;
> modeset_list = dev;
> }
>
> /* free resources again */
> drmModeFreeResources(res);
> return 0;
> }
>
> /*
> * Now we dig deeper into setting up a single connector. As described earlier,
> * we need to check several things first:
> * * If the connector is currently unused, that is, no monitor is plugged in,
> * then we can ignore it.
> * * We have to find a suitable resolution and refresh-rate. All this is
> * available in drmModeModeInfo structures saved for each crtc. We simply
> * use the first mode that is available. This is always the mode with the
> * highest resolution.
> * A more sophisticated mode-selection should be done in real applications,
> * though.
> * * Then we need to find an CRTC that can drive this connector. A CRTC is an
> * internal resource of each graphics-card. The number of CRTCs controls how
> * many connectors can be controlled indepedently. That is, a graphics-cards
> * may have more connectors than CRTCs, which means, not all monitors can be
> * controlled independently.
> * There is actually the possibility to control multiple connectors via a
> * single CRTC if the monitors should display the same content. However, we
> * do not make use of this here.
> * So think of connectors as pipelines to the connected monitors and the
> * CRTCs are the controllers that manage which data goes to which pipeline.
> * If there are more pipelines than CRTCs, then we cannot control all of
> * them at the same time.
> * * We need to create a framebuffer for this connector. A framebuffer is a
> * memory buffer that we can write XRGB32 data into. So we use this to
> * render our graphics and then the CRTC can scan-out this data from the
> * framebuffer onto the monitor.
> */
>
> static int modeset_setup_dev(int fd, drmModeRes *res, drmModeConnector *conn,
> struct modeset_dev *dev)
> {
> int ret;
>
> /* check if a monitor is connected */
> if (conn->connection != DRM_MODE_CONNECTED) {
> fprintf(stderr, "ignoring unused connector %u\n",
> conn->connector_id);
> return -ENOENT;
> }
>
> /* check if there is at least one valid mode */
> if (conn->count_modes == 0) {
> fprintf(stderr, "no valid mode for connector %u\n",
> conn->connector_id);
> return -EFAULT;
> }
>
> /* copy the mode information into our device structure */
> memcpy(&dev->mode, &conn->modes[0], sizeof(dev->mode));
> dev->width = conn->modes[0].hdisplay;
> dev->height = conn->modes[0].vdisplay;
> fprintf(stderr, "mode for connector %u is %ux%u\n",
> conn->connector_id, dev->width, dev->height);
>
> /* find a crtc for this connector */
> ret = modeset_find_crtc(fd, res, conn, dev);
> if (ret) {
> fprintf(stderr, "no valid crtc for connector %u\n",
> conn->connector_id);
> return ret;
> }
>
> /* create a framebuffer for this CRTC */
> ret = modeset_create_fb(fd, dev);
> if (ret) {
> fprintf(stderr, "cannot create framebuffer for connector %u\n",
> conn->connector_id);
> return ret;
> }
>
> return 0;
> }
>
> /*
> * modeset_find_crtc(fd, res, conn, dev): This small helper tries to find a
> * suitable CRTC for the given connector. We have actually have to introduce one
> * more DRM object to make this more clear: Encoders.
> * Encoders help the CRTC to convert data from a framebuffer into the right
> * format that can be used for the chosen connector. We do not have to
> * understand any more of these conversions to make use of it. However, you must
> * know that each connector has a limited list of encoders that it can use. And
> * each encoder can only work with a limited list of CRTCs. So what we do is
> * trying each encoder that is available and looking for a CRTC that this
> * encoder can work with. If we find the first working combination, we are happy
> * and write it into the @dev structure.
> * But before iterating all available encoders, we first try the currently
> * active encoder+crtc on a connector to avoid a full modeset.
> *
> * However, before we can use a CRTC we must make sure that no other device,
> * that we setup previously, is already using this CRTC. Remember, we can only
> * drive one connector per CRTC! So we simply iterate through the "modeset_list"
> * of previously setup devices and check that this CRTC wasn't used before.
> * Otherwise, we continue with the next CRTC/Encoder combination.
> */
>
> static int modeset_find_crtc(int fd, drmModeRes *res, drmModeConnector *conn,
> struct modeset_dev *dev)
> {
> drmModeEncoder *enc;
> unsigned int i, j;
> int32_t crtc;
> struct modeset_dev *iter;
>
> /* first try the currently conected encoder+crtc */
> if (conn->encoder_id)
> enc = drmModeGetEncoder(fd, conn->encoder_id);
> else
> enc = NULL;
>
> if (enc) {
> if (enc->crtc_id) {
> crtc = enc->crtc_id;
> for (iter = modeset_list; iter; iter = iter->next) {
> if (iter->crtc == crtc) {
> crtc = -1;
> break;
> }
> }
>
> if (crtc >= 0) {
> drmModeFreeEncoder(enc);
> dev->crtc = crtc;
> return 0;
> }
> }
>
> drmModeFreeEncoder(enc);
> }
>
> /* If the connector is not currently bound to an encoder or if the
> * encoder+crtc is already used by another connector (actually unlikely
> * but lets be safe), iterate all other available encoders to find a
> * matching CRTC. */
> for (i = 0; i < conn->count_encoders; ++i) {
> enc = drmModeGetEncoder(fd, conn->encoders[i]);
> if (!enc) {
> fprintf(stderr, "cannot retrieve encoder %u:%u (%d): %m\n",
> i, conn->encoders[i], errno);
> continue;
> }
>
> /* iterate all global CRTCs */
> for (j = 0; j < res->count_crtcs; ++j) {
> /* check whether this CRTC works with the encoder */
> if (!(enc->possible_crtcs & (1 << j)))
> continue;
>
> /* check that no other device already uses this CRTC */
> crtc = res->crtcs[j];
> for (iter = modeset_list; iter; iter = iter->next) {
> if (iter->crtc == crtc) {
> crtc = -1;
> break;
> }
> }
>
> /* we have found a CRTC, so save it and return */
> if (crtc >= 0) {
> drmModeFreeEncoder(enc);
> dev->crtc = crtc;
> return 0;
> }
> }
>
> drmModeFreeEncoder(enc);
> }
>
> fprintf(stderr, "cannot find suitable CRTC for connector %u\n",
> conn->connector_id);
> return -ENOENT;
> }
>
> /*
> * modeset_create_fb(fd, dev): After we have found a crtc+connector+mode
> * combination, we need to actually create a suitable framebuffer that we can
> * use with it. There are actually two ways to do that:
> * * We can create a so called "dumb buffer". This is a buffer that we can
> * memory-map via mmap() and every driver supports this. We can use it for
> * unaccelerated software rendering on the CPU.
> * * We can use libgbm to create buffers available for hardware-acceleration.
> * libgbm is an abstraction layer that creates these buffers for each
> * available DRM driver. As there is no generic API for this, each driver
> * provides its own way to create these buffers.
> * We can then use such buffers to create OpenGL contexts with the mesa3D
> * library.
> * We use the first solution here as it is much simpler and doesn't require any
> * external libraries. However, if you want to use hardware-acceleration via
> * OpenGL, it is actually pretty easy to create such buffers with libgbm and
> * libEGL. But this is beyond the scope of this document.
> *
> * So what we do is requesting a new dumb-buffer from the driver. We specify the
> * same size as the current mode that we selected for the connector.
> * Then we request the driver to prepare this buffer for memory mapping. After
> * that we perform the actual mmap() call. So we can now access the framebuffer
> * memory directly via the dev->map memory map.
> */
>
> static int modeset_create_fb(int fd, struct modeset_dev *dev)
> {
> struct drm_mode_create_dumb creq;
> struct drm_mode_destroy_dumb dreq;
> struct drm_mode_map_dumb mreq;
> int ret;
>
> /* create dumb buffer */
> memset(&creq, 0, sizeof(creq));
> creq.width = dev->width;
> creq.height = dev->height;
> creq.bpp = 8;
> ret = drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &creq);
> if (ret < 0) {
> fprintf(stderr, "cannot create dumb buffer (%d): %m\n",
> errno);
> return -errno;
> }
> dev->stride = creq.pitch;
> dev->size = creq.size;
> dev->handle = creq.handle;
>
> /* create framebuffer object for the dumb-buffer */
> ret = drmModeAddFB(fd, dev->width, dev->height, 8, 8, dev->stride,
> dev->handle, &dev->fb);
> if (ret) {
> fprintf(stderr, "cannot create framebuffer (%d): %m\n",
> errno);
> ret = -errno;
> goto err_destroy;
> }
>
> /* prepare buffer for memory mapping */
> memset(&mreq, 0, sizeof(mreq));
> mreq.handle = dev->handle;
> ret = drmIoctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &mreq);
> if (ret) {
> fprintf(stderr, "cannot map dumb buffer (%d): %m\n",
> errno);
> ret = -errno;
> goto err_fb;
> }
>
> /* perform actual memory mapping */
> dev->map = mmap(0, dev->size, PROT_READ | PROT_WRITE, MAP_SHARED,
> fd, mreq.offset);
> if (dev->map == MAP_FAILED) {
> fprintf(stderr, "cannot mmap dumb buffer (%d): %m\n",
> errno);
> ret = -errno;
> goto err_fb;
> }
>
> /* clear the framebuffer to 0 */
> memset(dev->map, 0, dev->size);
>
> return 0;
>
> err_fb:
> drmModeRmFB(fd, dev->fb);
> err_destroy:
> memset(&dreq, 0, sizeof(dreq));
> dreq.handle = dev->handle;
> drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &dreq);
> return ret;
> }
>
> /*
> * Finally! We have a connector with a suitable CRTC. We know which mode we want
> * to use and we have a framebuffer of the correct size that we can write to.
> * There is nothing special left to do. We only have to program the CRTC to
> * connect each new framebuffer to each selected connector for each combination
> * that we saved in the global modeset_list.
> * This is done with a call to drmModeSetCrtc().
> *
> * So we are ready for our main() function. First we check whether the user
> * specified a DRM device on the command line, otherwise we use the default
> * /dev/dri/card0. Then we open the device via modeset_open(). modeset_prepare()
> * prepares all connectors and we can loop over "modeset_list" and call
> * drmModeSetCrtc() on every CRTC/connector combination.
> *
> * But printing empty black pages is boring so we have another helper function
> * modeset_draw() that draws some colors into the framebuffer for 5 seconds and
> * then returns. And then we have all the cleanup functions which correctly free
> * all devices again after we used them. All these functions are described below
> * the main() function.
> *
> * As a side note: drmModeSetCrtc() actually takes a list of connectors that we
> * want to control with this CRTC. We pass only one connector, though. As
> * explained earlier, if we used multiple connectors, then all connectors would
> * have the same controlling framebuffer so the output would be cloned. This is
> * most often not what you want so we avoid explaining this feature here.
> * Furthermore, all connectors will have to run with the same mode, which is
> * also often not guaranteed. So instead, we only use one connector per CRTC.
> *
> * Before calling drmModeSetCrtc() we also save the current CRTC configuration.
> * This is used in modeset_cleanup() to restore the CRTC to the same mode as was
> * before we changed it.
> * If we don't do this, the screen will stay blank after we exit until another
> * application performs modesetting itself.
> */
>
> int main(int argc, char **argv)
> {
> int ret, fd;
> const char *card;
> struct modeset_dev *iter;
>
> /* check which DRM device to open */
> if (argc > 1)
> card = argv[1];
> else
> card = "/dev/dri/card0";
>
> fprintf(stderr, "using card '%s'\n", card);
>
> /* open the DRM device */
> ret = modeset_open(&fd, card);
> if (ret)
> goto out_return;
>
> /* prepare all connectors and CRTCs */
> ret = modeset_prepare(fd);
> if (ret)
> goto out_close;
>
> /* perform actual modesetting on each found connector+CRTC */
> for (iter = modeset_list; iter; iter = iter->next) {
> iter->saved_crtc = drmModeGetCrtc(fd, iter->crtc);
> ret = drmModeSetCrtc(fd, iter->crtc, iter->fb, 0, 0,
> &iter->conn, 1, &iter->mode);
> if (ret)
> fprintf(stderr, "cannot set CRTC for connector %u (%d): %m\n",
> iter->conn, errno);
> }
>
> /* draw some colors for 5seconds */
> modeset_draw(fd);
>
> /* cleanup everything */
> modeset_cleanup(fd);
>
> ret = 0;
>
> out_close:
> close(fd);
> out_return:
> if (ret) {
> errno = -ret;
> fprintf(stderr, "modeset failed with error %d: %m\n", errno);
> } else {
> fprintf(stderr, "exiting\n");
> }
> return ret;
> }
>
> /*
> * A short helper function to compute a changing color value. No need to
> * understand it.
> */
>
> static uint8_t next_color(bool *up, uint8_t cur, unsigned int mod)
> {
> uint8_t next;
>
> next = cur + (*up ? 1 : -1) * (rand() % mod);
> if ((*up && next < cur) || (!*up && next > cur)) {
> *up = !*up;
> next = cur;
> }
>
> return next;
> }
>
> static void crtc_lut(int fd, struct modeset_dev *dev, int p)
> {
> struct drm_mode_crtc_lut clut;
> uint16_t r[256];
> uint16_t g[256];
> uint16_t b[256];
> int ret;
> int i;
>
> /* prepare buffer for memory mapping */
> memset(&clut, 0, sizeof(clut));
> clut.crtc_id = dev->crtc;
> clut.gamma_size = 256;
> clut.red = (uint64_t)r;
> clut.green = (uint64_t)g;
> clut.blue = (uint64_t)b;
>
> for (i = 0; i < 256; ++i) {
> r[i] = ((p + 2 * i) & 255) * 257;
> g[i] = ((p + 3 * i) & 255) * 257;
> b[i] = ((p + 5 * i) & 255) * 257;
> }
> ret = drmIoctl(fd, DRM_IOCTL_MODE_SETGAMMA, &clut);
> if (ret)
> fprintf(stderr, "cannot set gamma lut (%d): %m\n",
> errno);
> }
>
> /*
> * modeset_draw(): This draws a solid color into all configured framebuffers.
> * Every 100ms the color changes to a slightly different color so we get some
> * kind of smoothly changing color-gradient.
> *
> * The color calculation can be ignored as it is pretty boring. So the
> * interesting stuff is iterating over "modeset_list" and then through all lines
> * and width. We then set each pixel individually to the current color.
> *
> * We do this 50 times as we sleep 100ms after each redraw round. This makes
> * 50*100ms = 5000ms = 5s so it takes about 5seconds to finish this loop.
> *
> * Please note that we draw directly into the framebuffer. This means that you
> * will see flickering as the monitor might refresh while we redraw the screen.
> * To avoid this you would need to use two framebuffers and a call to
> * drmModeSetCrtc() to switch between both buffers.
> * You can also use drmModePageFlip() to do a vsync'ed pageflip. But this is
> * beyond the scope of this document.
> */
>
> static void modeset_draw(int fd)
> {
> uint8_t p = 0;
> unsigned int i, j, k;
> struct modeset_dev *iter;
>
> for (iter = modeset_list; iter; iter = iter->next) {
> for (k = 0; k < iter->width; ++k) {
> for (j = 0; j < iter->height / 3; ++j) {
> iter->map[iter->stride * j + k] =
> k * 256 / iter->width;
> }
> for (; j < iter->height; ++j)
> iter->map[iter->stride * j + k] = 26;
> }
> }
>
> for (i = 0; i < 50; ++i, ++p) {
> for (iter = modeset_list; iter; iter = iter->next)
> crtc_lut(fd, iter, p);
>
> usleep(100000);
> }
> }
>
> /*
> * modeset_cleanup(fd): This cleans up all the devices we created during
> * modeset_prepare(). It resets the CRTCs to their saved states and deallocates
> * all memory.
> * It should be pretty obvious how all of this works.
> */
>
> static void modeset_cleanup(int fd)
> {
> struct modeset_dev *iter;
> struct drm_mode_destroy_dumb dreq;
>
> while (modeset_list) {
> /* remove from global list */
> iter = modeset_list;
> modeset_list = iter->next;
>
> /* restore saved CRTC configuration */
> drmModeSetCrtc(fd,
> iter->saved_crtc->crtc_id,
> iter->saved_crtc->buffer_id,
> iter->saved_crtc->x,
> iter->saved_crtc->y,
> &iter->conn,
> 1,
> &iter->saved_crtc->mode);
> drmModeFreeCrtc(iter->saved_crtc);
>
> /* unmap buffer */
> munmap(iter->map, iter->size);
>
> /* delete framebuffer */
> drmModeRmFB(fd, iter->fb);
>
> /* delete dumb buffer */
> memset(&dreq, 0, sizeof(dreq));
> dreq.handle = iter->handle;
> drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &dreq);
>
> /* free allocated memory */
> free(iter);
> }
> }
>
> /*
> * I hope this was a short but easy overview of the DRM modesetting API. The DRM
> * API offers much more capabilities including:
> * - double-buffering or tripple-buffering (or whatever you want)
> * - vsync'ed page-flips
> * - hardware-accelerated rendering (for example via OpenGL)
> * - output cloning
> * - graphics-clients plus authentication
> * - DRM planes/overlays/sprites
> * - ...
> * If you are interested in these topics, I can currently only redirect you to
> * existing implementations, including:
> * - plymouth (which uses dumb-buffers like this example; very easy to understand)
> * - kmscon (which uses libuterm to do this)
> * - wayland (very sophisticated DRM renderer; hard to understand fully as it
> * uses more complicated techniques like DRM planes)
> * - xserver (very hard to understand as it is split across many files/projects)
> *
> * But understanding how modesetting (as described in this document) works, is
> * essential to understand all further DRM topics.
> *
> * Any feedback is welcome. Feel free to use this code freely for your own
> * documentation or projects.
> *
> * - Hosted on http://github.com/dvdhrm/docs
> * - Written by David Herrmann <dh.herrmann@googlemail.com>
> */
> ----------------8<---------------
>
> Peter Rosin (3):
> drm: atmel-hlcdc: add support for 8-bit color lookup table mode
> drm/fb-cma-helper: expose more of fb cma guts
> drm: atmel-hlcdc: add clut support for legacy fbdev
>
> drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c | 58 +++++++++++++++++++++++++
> drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c | 25 ++++++++++-
> drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.h | 20 +++++++++
> drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c | 29 +++++++++++++
> drivers/gpu/drm/drm_fb_cma_helper.c | 55 ++++++++++++++++++-----
> include/drm/drm_fb_cma_helper.h | 8 +++-
> 6 files changed, 182 insertions(+), 13 deletions(-)
>