[PATCH 9/9] drm/udl: Support adapters without firmware descriptor

[Patrik Jakobsson]

On Tue, Apr 1, 2025 at 6:23 PM Thomas Zimmermann <tzimmermann at suse.de> wrote:
>
> Set default limit on the number of pixels for adapters without
> vendor firmware descriptor. The devices work as expected, they
> just don't provide any description.
>
> If parsing the vendor firmware descriptor fails, the device falls
> back to the given default limits. Failing to allocate memory is
> still an error.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>  drivers/gpu/drm/udl/udl_main.c | 37 +++++++++++++++++++---------------
>  1 file changed, 21 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/udl/udl_main.c b/drivers/gpu/drm/udl/udl_main.c
> index b5a6b254a2028..2685608af8cec 100644
> --- a/drivers/gpu/drm/udl/udl_main.c
> +++ b/drivers/gpu/drm/udl/udl_main.c
> @@ -76,6 +76,7 @@ static int udl_parse_vendor_descriptor(struct udl_device *udl)
>  {
>         struct drm_device *dev = &udl->drm;
>         struct usb_device *udev = udl_to_usb_device(udl);
> +       bool detected = false;
>         void *buf;
>         int ret;
>         unsigned int len;
> @@ -84,16 +85,16 @@ static int udl_parse_vendor_descriptor(struct udl_device *udl)
>
>         buf = kzalloc(MAX_VENDOR_DESCRIPTOR_SIZE, GFP_KERNEL);
>         if (!buf)
> -               return false;
> +               return -ENOMEM;
>
>         ret = usb_get_descriptor(udev, 0x5f, /* vendor specific */
>                                  0, buf, MAX_VENDOR_DESCRIPTOR_SIZE);
>         if (ret < 0)
> -               goto unrecognized;
> +               goto out;
>         len = ret;
>
>         if (len < 5)
> -               goto unrecognized;
> +               goto out;
>
>         desc = buf;
>         desc_end = desc + len;
> @@ -103,21 +104,20 @@ static int udl_parse_vendor_descriptor(struct udl_device *udl)
>             (desc[2] != 0x01) ||   /* version (2 bytes) */
>             (desc[3] != 0x00) ||
>             (desc[4] != len - 2))  /* length after type */
> -               goto unrecognized;
> +               goto out;
>         desc += 5;
>
> +       detected = true;
> +
>         while (desc < desc_end)
>                 desc = udl_parse_key_value_pair(udl, desc, desc_end);
>
> -       goto success;
> -
> -unrecognized:
> -       /* allow udlfb to load for now even if firmware unrecognized */
> -       drm_warn(dev, "Unrecognized vendor firmware descriptor\n");
> -
> -success:
> +out:
> +       if (!detected)
> +               drm_warn(dev, "Unrecognized vendor firmware descriptor\n");
>         kfree(buf);
> -       return true;
> +
> +       return 0;
>  }
>
>  /*
> @@ -345,11 +345,16 @@ int udl_init(struct udl_device *udl)
>                 drm_warn(dev, "buffer sharing not supported"); /* not an error */
>         }
>
> -       if (!udl_parse_vendor_descriptor(udl)) {
> -               ret = -ENODEV;
> -               DRM_ERROR("firmware not recognized. Assume incompatible device\n");
> +       /*
> +        * Not all devices provide vendor descriptors with device
> +        * information. Initialize to default values from real-world
> +        * devices. It is just enough memory for FullHD.
> +        */
> +       udl->sku_pixel_limit = USL_SKU_PIXEL_LIMIT_DEFAULT;

Should be UDL_SKU_PIXEL_LIMIT_DEFAULT

> +
> +       ret = udl_parse_vendor_descriptor(udl);
> +       if (ret)
>                 goto err;
> -       }
>
>         if (udl_select_std_channel(udl))
>                 DRM_ERROR("Selecting channel failed\n");
> --
> 2.49.0
>