hw/display: add ramfb, a simple boot framebuffer living in guest ram

The boot framebuffer is expected to be configured by the firmware, so it
uses fw_cfg as interface.  Initialization goes as follows:

  (1) Check whenever etc/ramfb is present.
  (2) Allocate framebuffer from RAM.
  (3) Fill struct RAMFBCfg, write it to etc/ramfb.

Done.  You can write stuff to the framebuffer now, and it should appear
automagically on the screen.

Note that this isn't very efficient because it does a full display
update on each refresh.  No dirty tracking.  Dirty tracking would have
to be active for the whole ram slot, so that wouldn't be very efficient
either.  For a boot display which is active for a short time only this
isn't a big deal.  As permanent guest display something better should be
used (if possible).

This is the ramfb core code.  Some windup is needed for display devices
which want have a ramfb boot display.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Message-id: 20180613122948.18149-2-kraxel@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/display/Makefile.objs

+common-obj-y += ramfb.o
+
 common-obj-$(CONFIG_ADS7846) += ads7846.o
 common-obj-$(CONFIG_VGA_CIRRUS) += cirrus_vga.o
 common-obj-$(CONFIG_G364FB) += g364fb.o

hw/display/ramfb.c

+/*
+ * early boot framebuffer in guest ram
+ * configured using fw_cfg
+ *
+ * Copyright Red Hat, Inc. 2017
+ *
+ * Author:
+ *     Gerd Hoffmann <kraxel@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "hw/loader.h"
+#include "hw/display/ramfb.h"
+#include "ui/console.h"
+#include "sysemu/sysemu.h"
+
+struct QEMU_PACKED RAMFBCfg {
+    uint64_t addr;
+    uint32_t fourcc;
+    uint32_t flags;
+    uint32_t width;
+    uint32_t height;
+    uint32_t stride;
+};
+
+struct RAMFBState {
+    DisplaySurface *ds;
+    uint32_t width, height;
+    struct RAMFBCfg cfg;
+};
+
+static void ramfb_fw_cfg_write(void *dev, off_t offset, size_t len)
+{
+    RAMFBState *s = dev;
+    void *framebuffer;
+    uint32_t stride, fourcc, format;
+    hwaddr addr, length;
+
+    s->width  = be32_to_cpu(s->cfg.width);
+    s->height = be32_to_cpu(s->cfg.height);
+    stride    = be32_to_cpu(s->cfg.stride);
+    fourcc    = be32_to_cpu(s->cfg.fourcc);
+    addr      = be64_to_cpu(s->cfg.addr);
+    length    = stride * s->height;
+    format    = qemu_drm_format_to_pixman(fourcc);
+
+    fprintf(stderr, "%s: %dx%d @ 0x%" PRIx64 "\n", __func__,
+            s->width, s->height, addr);
+    framebuffer = address_space_map(&address_space_memory,
+                                    addr, &length, false,
+                                    MEMTXATTRS_UNSPECIFIED);
+    if (!framebuffer || length < stride * s->height) {
+        s->width = 0;
+        s->height = 0;
+        return;
+    }
+    s->ds = qemu_create_displaysurface_from(s->width, s->height,
+                                            format, stride, framebuffer);
+}
+
+void ramfb_display_update(QemuConsole *con, RAMFBState *s)
+{
+    if (!s->width || !s->height) {
+        return;
+    }
+
+    if (s->ds) {
+        dpy_gfx_replace_surface(con, s->ds);
+        s->ds = NULL;
+    }
+
+    /* simple full screen update */
+    dpy_gfx_update_full(con);
+}
+
+RAMFBState *ramfb_setup(Error **errp)
+{
+    FWCfgState *fw_cfg = fw_cfg_find();
+    RAMFBState *s;
+
+    if (!fw_cfg || !fw_cfg->dma_enabled) {
+        error_setg(errp, "ramfb device requires fw_cfg with DMA");
+        return NULL;
+    }
+
+    s = g_new0(RAMFBState, 1);
+
+    fw_cfg_add_file_callback(fw_cfg, "etc/ramfb",
+                             NULL, ramfb_fw_cfg_write, s,
+                             &s->cfg, sizeof(s->cfg), false);
+    return s;
+}

include/hw/display/ramfb.h

+#ifndef RAMFB_H
+#define RAMFB_H
+
+/* ramfb.c */
+typedef struct RAMFBState RAMFBState;
+void ramfb_display_update(QemuConsole *con, RAMFBState *s);
+RAMFBState *ramfb_setup(Error **errp);
+
+#endif /* RAMFB_H */