[PATCH v2 8/9] drm/simpledrm: Support virtual screen sizes

[Noralf Trønnes]

Den 01.11.2021 15.15, skrev Thomas Zimmermann:
> Add constants for the maximum size of the shadow-plane surface
> size. Useful for shadow planes with virtual screen sizes. The
> current sizes are 4096 scanlines with 4096 pixels each. This
> seems reasonable for current hardware, but can be increased as
> necessary.
> 
> In simpledrm, set the maximum framebuffer size from the constants
> for shadow planes. Implements support for virtual screen sizes and
> page flipping on the fbdev console.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>  drivers/gpu/drm/tiny/simpledrm.c    |  9 +++++++--
>  include/drm/drm_gem_atomic_helper.h | 18 ++++++++++++++++++
>  2 files changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
> index e872121e9fb0..e42ae1c6ebcd 100644
> --- a/drivers/gpu/drm/tiny/simpledrm.c
> +++ b/drivers/gpu/drm/tiny/simpledrm.c
> @@ -2,6 +2,7 @@
>  
>  #include <linux/clk.h>
>  #include <linux/of_clk.h>
> +#include <linux/minmax.h>
>  #include <linux/platform_data/simplefb.h>
>  #include <linux/platform_device.h>
>  #include <linux/regulator/consumer.h>
> @@ -776,6 +777,7 @@ static int simpledrm_device_init_modeset(struct simpledrm_device *sdev)
>  	struct drm_display_mode *mode = &sdev->mode;
>  	struct drm_connector *connector = &sdev->connector;
>  	struct drm_simple_display_pipe *pipe = &sdev->pipe;
> +	unsigned long max_width, max_height;
>  	const uint32_t *formats;
>  	size_t nformats;
>  	int ret;
> @@ -784,10 +786,13 @@ static int simpledrm_device_init_modeset(struct simpledrm_device *sdev)
>  	if (ret)
>  		return ret;
>  
> +	max_width = max_t(unsigned long, mode->hdisplay, DRM_SHADOW_PLANE_MAX_WIDTH);
> +	max_height = max_t(unsigned long, mode->vdisplay, DRM_SHADOW_PLANE_MAX_HEIGHT);
> +
>  	dev->mode_config.min_width = mode->hdisplay;
> -	dev->mode_config.max_width = mode->hdisplay;
> +	dev->mode_config.max_width = max_width;
>  	dev->mode_config.min_height = mode->vdisplay;
> -	dev->mode_config.max_height = mode->vdisplay;
> +	dev->mode_config.max_height = max_height;
>  	dev->mode_config.prefer_shadow_fbdev = true;
>  	dev->mode_config.preferred_depth = sdev->format->cpp[0] * 8;
>  	dev->mode_config.funcs = &simpledrm_mode_config_funcs;
> diff --git a/include/drm/drm_gem_atomic_helper.h b/include/drm/drm_gem_atomic_helper.h
> index 48222a107873..54983ecf641a 100644
> --- a/include/drm/drm_gem_atomic_helper.h
> +++ b/include/drm/drm_gem_atomic_helper.h
> @@ -22,6 +22,24 @@ int drm_gem_simple_display_pipe_prepare_fb(struct drm_simple_display_pipe *pipe,
>   * Helpers for planes with shadow buffers
>   */
>  
> +/**
> + * DRM_SHADOW_PLANE_MAX_WIDTH - Maximum width of a plane's shadow buffer in pixels
> + *
> + * For drivers with shadow planes, the maximum width of the framebuffer is
> + * usually independent from hardware limitations. Drivers can initialize struct
> + * drm_mode_config.max_width from DRM_SHADOW_PLANE_MAX_WIDTH.

Why would a driver do that instead of using a value of its own? Is it
some kind of standardization?

> + */
> +#define DRM_SHADOW_PLANE_MAX_WIDTH	(1ul << 12)

Please use a decimal number, I'm so slow at doing this in my head that I
use bash to calculate it for me, which really slows down parsing the code.

Noralf.

> +
> +/**
> + * DRM_SHADOW_PLANE_MAX_HEIGHT - Maximum height of a plane's shadow buffer in scanlines
> + *
> + * For drivers with shadow planes, the maximum height of the framebuffer is
> + * usually independent from hardware limitations. Drivers can initialize struct
> + * drm_mode_config.max_height from DRM_SHADOW_PLANE_MAX_HEIGHT.
> + */
> +#define DRM_SHADOW_PLANE_MAX_HEIGHT	(1ul << 12)
> +
>  /**
>   * struct drm_shadow_plane_state - plane state for planes with shadow buffers
>   *
>