Hello Eric,
On 04/19/2016 03:19 PM, Eric Anholt wrote:
> With simplefb and vc4 both enabled, simplefb would probe first and be
> fb0, displaying for a moment before vc4 probed fb1 and reconfigured
> the graphics hardware so that only its fbdev worked.
>
> Cc: javier@xxxxxxxxxxxxxxx
>
> Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>
> ---
>
> Ccing Javier, since it looks like Exynos has also had this trouble,
> and may want to get some compatible string in the list.
>
That's correct, we had the same issue on some Exynos5250 Chromebooks
(Snow and Spring) where the vendor provided u-boot binaries that had
simplefb support, so users were relying on simplefb and things broke
when proper DRM support for the platform was introduced in mainline.
> drivers/video/fbdev/simplefb.c | 33 +++++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
> index e9cf19977285..a2971aa686f5 100644
> --- a/drivers/video/fbdev/simplefb.c
> +++ b/drivers/video/fbdev/simplefb.c
> @@ -512,11 +512,44 @@ static struct platform_driver simplefb_driver = {
> .remove = simplefb_remove,
> };
>
> +/* Returns true if a simplefb node that's present should be ignored.
> + *
> + * The U-Boot bootloader, and possibly others, may add a simplefb
> + * device node to the existing device tree based on the video
> + * configuration initialized by the firmware. If we have a native
> + * driver for graphics, then simplefb would just be writing into
> + * memory that's no longer being scanned out.
> + */
> +static bool
> +simplefb_superseded(void)
> +{
> + static const char *compats[] __initconst = {
> +#ifdef CONFIG_DRM_VC4
I think this should be #if IS_ENABLED(CONFIG_DRM_VC4) since you will
have the same issue if the VC4 DRM driver is built as a module, once
the module is loaded. Your current patch only will works if built-in.
> + "brcm,bcm2835-vc4",
> +#endif
> + };
> + struct device_node *node;
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(compats); i++) {
> + node = of_find_compatible_node(NULL, NULL, compats[i]);
> + if (node) {
> + of_node_put(node);
> + return true;
> + }
> + }
> +
> + return false;
> +}
> +
> static int __init simplefb_init(void)
> {
> int ret;
> struct device_node *np;
>
> + if (simplefb_superseded())
> + return 0;
> +
I wonder if this is the correct approach though, for example in the module
case I mentioned before, the user won't have display working if something
happens that prevents the module to be loaded (i.e: wrong module install).
It would be better if there is a way to do a hand-off between the drivers,
something like what happens with earlyprintk and the real serial console.
> ret = platform_driver_register(&simplefb_driver);
> if (ret)
> return ret;
>
Best regards,
--
Javier Martinez Canillas
Open Source Group
Samsung Research America
--
To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
