[2/4] ramfb: Add driver for ramfb display

QEMU implements multiple ways to expose graphics output to the virt
machine, but most of them are incompatible with hardware virtualization.

The one that does work reliably is ramfb. It's a very simple mechanism
in which the guest reserves a memory region for the frame buffer and then
notifies the host about its location and properties. The host then just
displays the contents of the frame buffer on screen.

This patch implements a trivial version of a ramfb driver - hard coded
to a single resolution.

Signed-off-by: Alexander Graf <agraf@csgraf.de>
---
 drivers/video/Kconfig     |   8 +++
 drivers/video/MAINTAINERS |   4 ++
 drivers/video/Makefile    |   1 +
 drivers/video/ramfb.c     | 104 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 117 insertions(+)
 create mode 100644 drivers/video/MAINTAINERS
 create mode 100644 drivers/video/ramfb.c

Hi Alex,

On Sun, 27 Feb 2022 at 07:40, Alexander Graf <agraf@csgraf.de> wrote:
>
> QEMU implements multiple ways to expose graphics output to the virt
> machine, but most of them are incompatible with hardware virtualization.
>
> The one that does work reliably is ramfb. It's a very simple mechanism
> in which the guest reserves a memory region for the frame buffer and then
> notifies the host about its location and properties. The host then just
> displays the contents of the frame buffer on screen.
>
> This patch implements a trivial version of a ramfb driver - hard coded
> to a single resolution.
>
> Signed-off-by: Alexander Graf <agraf@csgraf.de>
> ---
>  drivers/video/Kconfig     |   8 +++
>  drivers/video/MAINTAINERS |   4 ++
>  drivers/video/Makefile    |   1 +
>  drivers/video/ramfb.c     | 104 ++++++++++++++++++++++++++++++++++++++
>  4 files changed, 117 insertions(+)
>  create mode 100644 drivers/video/MAINTAINERS
>  create mode 100644 drivers/video/ramfb.c
>
> diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
> index ff8e11f648..73a9e20534 100644
> --- a/drivers/video/Kconfig
> +++ b/drivers/video/Kconfig
> @@ -871,6 +871,14 @@ config VIDEO_MCDE_SIMPLE
>           before u-boot starts, and u-boot will simply render to the pre-
>           allocated frame buffer surface.
>
> +config VIDEO_RAMFB
> +       bool "QEMU ramfb display driver for in-RAM display"
> +       depends on EFI_LOADER && DM_VIDEO && QFW
> +       help
> +         Enables a RAM based simple frame buffer driver which uses qfw to
> +         notify the hypervisor about the location of a Frame Buffer allocated
> +         in guest RAM as well as its properties.
> +
>  config OSD
>         bool "Enable OSD support"
>         depends on DM
> diff --git a/drivers/video/MAINTAINERS b/drivers/video/MAINTAINERS
> new file mode 100644
> index 0000000000..74c258a314
> --- /dev/null
> +++ b/drivers/video/MAINTAINERS
> @@ -0,0 +1,4 @@
> +QEMU RAMFB VIDEO DRIVER
> +M:     Alexander Graf <agraf@csgraf.de>
> +S:     Maintained
> +F:     drivers/video/ramfb.c
> diff --git a/drivers/video/Makefile b/drivers/video/Makefile
> index 4038395b12..6cfec17072 100644
> --- a/drivers/video/Makefile
> +++ b/drivers/video/Makefile
> @@ -74,6 +74,7 @@ obj-$(CONFIG_VIDEO_TEGRA20) += tegra.o
>  obj-$(CONFIG_VIDEO_VCXK) += bus_vcxk.o
>  obj-$(CONFIG_VIDEO_VESA) += vesa.o
>  obj-$(CONFIG_VIDEO_SEPS525) += seps525.o
> +obj-$(CONFIG_VIDEO_RAMFB) += ramfb.o
>
>  obj-y += bridge/
>  obj-y += sunxi/
> diff --git a/drivers/video/ramfb.c b/drivers/video/ramfb.c
> new file mode 100644
> index 0000000000..c46bfa3baa
> --- /dev/null
> +++ b/drivers/video/ramfb.c
> @@ -0,0 +1,104 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * (C) Copyright 2022 Alexander Graf
> + */
> +
> +#include <common.h>
> +#include <dm.h>
> +#include <log.h>
> +#include <video.h>
> +#include <asm/global_data.h>
> +#include <efi_loader.h>
> +#include <qfw.h>
> +
> +#define fourcc_code(a, b, c, d) ((u32)(a) | ((u32)(b) << 8) | \
> +                                ((u32)(c) << 16) | ((u32)(d) << 24))
> +#define DRM_FORMAT_XRGB8888 fourcc_code('X', 'R', '2', '4')
> +
> +#define DEFAULT_WIDTH  1280
> +#define DEFAULT_HEIGHT 900
> +#define DEFAULT_BPIX   VIDEO_BPP32
> +#define DEFAULT_FORMAT VIDEO_X8R8G8B8
> +
> +struct ramfb_cfg {

Should that be in a qemu header file somewhere? Anyway, please add comments.

> +       u64 addr;
> +       u32 fourcc;
> +       u32 flags;
> +       u32 width;
> +       u32 height;
> +       u32 stride;
> +} __packed;
> +
> +static int ramfb_probe(struct udevice *dev)
> +{
> +       struct video_uc_plat *plat = dev_get_uclass_plat(dev);
> +       struct video_priv *uc_priv = dev_get_uclass_priv(dev);
> +       u32 selector;
> +       u64 base;
> +       u64 size;
> +       efi_status_t ret;
> +       struct fw_file *file;
> +       struct udevice *qfw;
> +       struct dm_qfw_ops *ops;
> +       struct qfw_dma dma = {};
> +       struct ramfb_cfg cfg = {
> +               .addr = 0,
> +               .fourcc = cpu_to_be32(DRM_FORMAT_XRGB8888),
> +               .flags = 0,
> +               .width = cpu_to_be32(DEFAULT_WIDTH),
> +               .height = cpu_to_be32(DEFAULT_HEIGHT),
> +               .stride = 0,
> +       };
> +
> +       ret = qfw_get_dev(&qfw);
> +       if (ret)
> +               return -EPROBE_DEFER;
> +
> +       ops = dm_qfw_get_ops(qfw);
> +       if (!ops)
> +               return -EPROBE_DEFER;
> +
> +       file = qfw_find_file(qfw, "etc/ramfb");
> +       if (!file) {
> +               /* No ramfb available. At least we tried. */
> +               return -ENOENT;
> +       }
> +
> +       size = DEFAULT_WIDTH * DEFAULT_HEIGHT * VNBYTES(DEFAULT_BPIX);
> +       ret = efi_allocate_pages(EFI_ALLOCATE_ANY_PAGES,
> +                                EFI_RESERVED_MEMORY_TYPE,
> +                                efi_size_in_pages(size), &base);

Please see video-uclass.c for how to to allocate the frame buffer.
This has nothing to do with EFI.

> +       if (ret != EFI_SUCCESS)
> +               return -ENOMEM;
> +
> +       debug("%s: base=%llx, size=%llu\n", __func__, base, size);
> +
> +       cfg.addr = cpu_to_be64(base);
> +       plat->base = base;
> +       plat->size = size;
> +       uc_priv->xsize = DEFAULT_WIDTH;
> +       uc_priv->ysize = DEFAULT_HEIGHT;
> +       uc_priv->bpix = DEFAULT_BPIX;
> +       uc_priv->format = DEFAULT_FORMAT;
> +       uc_priv->fb = (void *)base;
> +       uc_priv->fb_size = size;
> +
> +       selector = be16_to_cpu(file->cfg.select);
> +       dma.length = cpu_to_be32(sizeof(cfg));
> +       dma.address = cpu_to_be64((uintptr_t)&cfg);
> +       dma.control = cpu_to_be32(FW_CFG_DMA_WRITE | FW_CFG_DMA_SELECT |
> +                                 (selector << 16));
> +
> +       barrier();
> +
> +       /* Send a DMA write request which enables the screen */
> +       ops->read_entry_dma(qfw, &dma);
> +
> +       return 0;
> +}
> +
> +U_BOOT_DRIVER(ramfb) = {
> +       .name   = "ramfb",
> +       .id     = UCLASS_VIDEO,
> +       .probe  = ramfb_probe,

You need a bind() method too.

> +};
> --
> 2.32.0
>

Regards,
Simon