[PATCH 08/10] drm: Add Generic USB Display driver

[Noralf Trønnes]

Den 29.04.2020 14.48, skrev Noralf Trønnes:
> This adds a generic USB display driver with the intention that it can be
> used with future USB interfaced low end displays/adapters. The Linux
> gadget device driver will serve as the canonical device implementation.
> 
> The following DRM properties are supported:
> - Plane rotation
> - Connector TV properties
> 
> There is also support for backlight brightness exposed as a backlight
> device.
> 
> Display modes can be made available to the host driver either as DRM
> display modes or through EDID. If both are present, EDID is just passed
> on to userspace.
> 
> Performance is preferred over color depth, so if the device supports
> RGB565, DRM_CAP_DUMB_PREFERRED_DEPTH will return 16.
> 
> If the device transfer buffer can't fit an uncompressed framebuffer
> update, the update is split up into parts that do fit.
> 
> Optimal user experience is achieved by providing damage reports either by
> setting FB_DAMAGE_CLIPS on pageflips or calling DRM_IOCTL_MODE_DIRTYFB.
> 
> LZ4 compression is used if the device supports it.
> 
> The driver supports a one bit monochrome transfer format: R1. This is not
> implemented in the gadget driver. It is added in preparation for future
> monochrome e-ink displays.
> 
> The driver is MIT licensed to smooth the path for any BSD port of the
> driver.
> 
> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
> ---

> diff --git a/drivers/gpu/drm/gud/gud_drm_drv.c b/drivers/gpu/drm/gud/gud_drm_drv.c

> +static int gud_drm_probe(struct usb_interface *interface,
> +			 const struct usb_device_id *id)
> +{

<snip>

> +	gdrm = kzalloc(sizeof(*gdrm), GFP_KERNEL);
> +	if (!gdrm)
> +		return -ENOMEM;
> +
> +	gdrm->usb = usb;
> +	gdrm->ifnum = interface->cur_altsetting->desc.bInterfaceNumber;
> +	gdrm->compression = desc.bCompression & GUD_DRM_COMPRESSION_LZ4;
> +
> +	drm = &gdrm->drm;
> +	ret = devm_drm_dev_init(dev, drm, &gud_drm_driver);
> +	if (ret) {
> +		kfree(gdrm);
> +		return ret;
> +	}

I see that Daniel's series has landed now, so I will use
devm_drm_dev_alloc() and drmm_mode_config_init() in the next version.

<snip>

> +	drm_fbdev_generic_setup(drm, 16);

This should be:

	drm_fbdev_generic_setup(drm, 0);

Noralf.

> +
> +	return 0;
> +}