Re: [PATCH 01/22] drm/fbdev-dma: Implement fbdev emulation for GEM DMA helpers

Javier Martinez Canillas
2023-03-09T11:25:22Z

Thomas Zimmermann <tzimmermann@suse.de> writes:

> Implement fbdev emulation that is optimized for drivers that use
> DMA helpers. The buffers may no tbe moveable, may not require damage

"may not be"

Is may the correct verb here though? I guess you meant "shall not".

> handling and have to be located in system memory. This allows fbdev
> emulation to operate directly on the buffer and mmap it to userspace.
>
> Besides those constraints, the emulation works like in the generic
> code. As an internal DRM client provides, it receives hotplug, restore
> and unregister events. The DRM client is independent from the fbdev
> probing, which runs on the first successful hotplug event.
>
> The emulation is part of the DMA helper module and not build unless
> DMA helpers and fbdev emulation has been configured.
>
> Tested with vc4.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---

[...]

> +static int drm_fbdev_dma_fb_open(struct fb_info *info, int user)
> +{
> + struct drm_fb_helper *fb_helper = info->par;
> +
> + /* No need to take a ref for fbcon because it unbinds on unregister */
> + if (user && !try_module_get(fb_helper->dev->driver->fops->owner))
> + return -ENODEV;
> +
> + return 0;
> +}
> +
> +static int drm_fbdev_dma_fb_release(struct fb_info *info, int user)
> +{
> + struct drm_fb_helper *fb_helper = info->par;
> +
> + if (user)
> + module_put(fb_helper->dev->driver->fops->owner);
> +
> + return 0;
> +}
> +

These two functions are the same than what's used by the generic fbdev
emulation. Maybe they could be moved to drivers/gpu/drm/drm_fb_helper.c
and be reused ?

> +static int drm_fbdev_dma_helper_fb_probe(struct drm_fb_helper *fb_helper,
> + struct drm_fb_helper_surface_size *sizes)
> +{
> + struct drm_client_dev *client = &fb_helper->client;
> + struct drm_device *dev = fb_helper->dev;
> + struct drm_client_buffer *buffer;
> + struct drm_gem_dma_object *dma_obj;
> + struct drm_framebuffer *fb;
> + struct fb_info *info;
> + u32 format;
> + struct iosys_map map;
> + int ret;
> +
> + drm_dbg_kms(dev, "surface width(%d), height(%d) and bpp(%d)\n",
> + sizes->surface_width, sizes->surface_height,
> + sizes->surface_bpp);
> +
> + format = drm_mode_legacy_fb_format(sizes->surface_bpp, sizes->surface_depth);
> + buffer = drm_client_framebuffer_create(client, sizes->surface_width,
> + sizes->surface_height, format);
> + if (IS_ERR(buffer))
> + return PTR_ERR(buffer);
> + dma_obj = to_drm_gem_dma_obj(buffer->gem);
> +
> + fb = buffer->fb;
> + if (drm_WARN_ON(dev, fb->funcs->dirty)) {
> + ret = -ENODEV; /* damage handling not supported; use generic emulation */
> + goto err_drm_client_buffer_delete;
> + }

Should we have a similar check for drm_fbdev_use_shadow_fb(fb_helper)
and warn on ?

> +
> + ret = drm_client_buffer_vmap(buffer, &map);
> + if (ret) {
> + goto err_drm_client_buffer_delete;
> + } else if (drm_WARN_ON(dev, map.is_iomem)) {
> + ret = -ENODEV; /* I/O memory not supported; use generic emulation */

I also wonder if here and above instead of the warn on, there should
just be a normal check and print more verbose warning messages.

[...]

> +static void drm_fbdev_dma_client_unregister(struct drm_client_dev *client)
> +{
> + struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
> +
> + if (fb_helper->info) {
> + drm_fb_helper_unregister_info(fb_helper);
> + } else {
> + drm_client_release(&fb_helper->client);
> + drm_fb_helper_unprepare(fb_helper);
> + kfree(fb_helper);
> + }
> +}

This is again the same than drm_fbdev_client_unregister() so I think
that can be made a helper and shared bewteen the two implementations.

> +
> +static int drm_fbdev_dma_client_restore(struct drm_client_dev *client)
> +{
> + drm_fb_helper_lastclose(client->dev);
> +
> + return 0;
> +}

Same for this one.

> +
> +static int drm_fbdev_dma_client_hotplug(struct drm_client_dev *client)
> +{
> + struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
> + struct drm_device *dev = client->dev;
> + int ret;
> +
> + if (dev->fb_helper)
> + return drm_fb_helper_hotplug_event(dev->fb_helper);
> +
> + ret = drm_fb_helper_init(dev, fb_helper);
> + if (ret)
> + goto err_drm_err;
> +
> + if (!drm_drv_uses_atomic_modeset(dev))
> + drm_helper_disable_unused_functions(dev);
> +
> + ret = drm_fb_helper_initial_config(fb_helper);
> + if (ret)
> + goto err_drm_fb_helper_fini;
> +
> + return 0;
> +
> +err_drm_fb_helper_fini:
> + drm_fb_helper_fini(fb_helper);
> +err_drm_err:
> + drm_err(dev, "fbdev-dma: Failed to setup generic emulation (ret=%d)\n", ret);
> + return ret;
> +}

And this one.

> +/**
> + * drm_fbdev_dma_setup() - Setup fbdev emulation for GEM DMA helpers
> + * @dev: DRM device
> + * @preferred_bpp: Preferred bits per pixel for the device.
> + * @dev->mode_config.preferred_depth is used if this is zero.
> + *
> + * This function sets up fbdev emulation for GEM DMA drivers that support
> + * dumb buffers with a virtual address and that can be mmap'ed.
> + * drm_fbdev_dma_setup() shall be called after the DRM driver registered
> + * the new DRM device with drm_dev_register().
> + *
> + * Restore, hotplug events and teardown are all taken care of. Drivers that do
> + * suspend/resume need to call drm_fb_helper_set_suspend_unlocked() themselves.
> + * Simple drivers might use drm_mode_config_helper_suspend().
> + *
> + * This function is safe to call even when there are no connectors present.
> + * Setup will be retried on the next hotplug event.
> + *
> + * The fbdev is destroyed by drm_dev_unregister().
> + */
> +void drm_fbdev_dma_setup(struct drm_device *dev, unsigned int preferred_bpp)
> +{
> + struct drm_fb_helper *fb_helper;
> + int ret;
> +
> + drm_WARN(dev, !dev->registered, "Device has not been registered.\n");
> + drm_WARN(dev, dev->fb_helper, "fb_helper is already set!\n");
> +
> + fb_helper = kzalloc(sizeof(*fb_helper), GFP_KERNEL);
> + if (!fb_helper)
> + return;
> + drm_fb_helper_prepare(dev, fb_helper, preferred_bpp, &drm_fbdev_dma_helper_funcs);
> +
> + ret = drm_client_init(dev, &fb_helper->client, "fbdev", &drm_fbdev_dma_client_funcs);
> + if (ret) {
> + drm_err(dev, "Failed to register client: %d\n", ret);
> + goto err_drm_client_init;
> + }
> +
> + ret = drm_fbdev_dma_client_hotplug(&fb_helper->client);
> + if (ret)
> + drm_dbg_kms(dev, "client hotplug ret=%d\n", ret);
> +
> + drm_client_register(&fb_helper->client);
> +
> + return;
> +
> +err_drm_client_init:
> + drm_fb_helper_unprepare(fb_helper);
> + kfree(fb_helper);
> +}
> +EXPORT_SYMBOL(drm_fbdev_dma_setup);

And this one could also be shared AFAICT if drm_fbdev_client_hotplug()
is used instead.

> diff --git a/include/drm/drm_fbdev_dma.h b/include/drm/drm_fbdev_dma.h
> new file mode 100644
> index 000000000000..2da7ee784133
> --- /dev/null
> +++ b/include/drm/drm_fbdev_dma.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: MIT */
> +
> +#ifndef DRM_FBDEV_DMA_H
> +#define DRM_FBDEV_DMA_H
> +
> +struct drm_device;
> +
> +#ifdef CONFIG_DRM_FBDEV_EMULATION
> +void drm_fbdev_dma_setup(struct drm_device *dev, unsigned int preferred_bpp);
> +#else
> +static inline void drm_fbdev_dma_setup(struct drm_device *dev, unsigned int preferred_bpp)
> +{ }
> +#endif
> +
> +#endif
> --

And you should be able to drop this header too if split the common
helpers from drm_fbdev_generic.c or maybe I'm missing something ?

--
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat