[Qemu-devel] [PATCH v2 3/7] hw/display: add ramfb, a simple boot framebuffer living in guest ram

[Gerd Hoffmann <kraxel@redhat.com>]

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.  So it is *really* intended to be only active for a short time
at boot, before the guest loaded the drivers for the real display
hardware.

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>
---
 include/hw/display/ramfb.h |  8 ++++
 hw/display/ramfb.c         | 95 ++++++++++++++++++++++++++++++++++++++++++++++
 hw/display/Makefile.objs   |  2 +
 3 files changed, 105 insertions(+)
 create mode 100644 include/hw/display/ramfb.h
 create mode 100644 hw/display/ramfb.c

diff --git a/include/hw/display/ramfb.h b/include/hw/display/ramfb.h
new file mode 100644
index 0000000000..f3a772e99e
--- /dev/null
+++ b/include/hw/display/ramfb.h
@@ -0,0 +1,8 @@
+#ifndef RAMFB_H
+#define RAMFB_H
+
+typedef struct RAMFBState RAMFBState;
+void ramfb_display_update(QemuConsole *con, RAMFBState *s);
+RAMFBState *ramfb_setup(Error **errp);
+
+#endif /* RAMFB_H */
diff --git a/hw/display/ramfb.c b/hw/display/ramfb.c
new file mode 100644
index 0000000000..5425e1feb1
--- /dev/null
+++ b/hw/display/ramfb.c
@@ -0,0 +1,95 @@
+/*
+ * 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 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);
+    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(con, 0, 0, s->width, s->height);
+}
+
+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);
+
+    rom_add_vga("vgabios-ramfb.bin");
+    fw_cfg_add_file_callback(fw_cfg, "etc/ramfb",
+                             NULL, ramfb_fw_cfg_write, s,
+                             &s->cfg, sizeof(s->cfg), false);
+    return s;
+}
diff --git a/hw/display/Makefile.objs b/hw/display/Makefile.objs
index 3c7c75b94d..fae17fd5ea 100644
--- a/hw/display/Makefile.objs
+++ b/hw/display/Makefile.objs
@@ -1,3 +1,5 @@
+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
-- 
2.9.3