On Fri, Jun 03, 2016 at 06:11:16PM +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@xxxxxxxxxx>
>
> FB helper code falls back to a 1024x768 mode if no outputs are connected
> or don't report back any modes upon initialization. This can be annoying
> because outputs that are added to FB helper later on can't be used with
> FB helper if they don't support a matching mode.
>
> The fallback is in place because VGA connectors can happen to report an
> unknown connection status even when they are in fact connected.
>
> Some drivers have custom solutions in place to defer FB helper setup
> until at least one output is connected. But the logic behind these
> solutions is always the same and there is nothing driver-specific about
> it, so a better alterative is to fix the FB helper core and add support
> for all drivers automatically.
>
> This patch adds support for deferred FB helper setup. It checks all the
> connectors for their connection status, and if all of them report to be
> disconnected marks the FB helper as needing deferred setup. Whet setup
> is deferred, the FB helper core will automatically retry setup after a
> hotplug event, and it will keep trying until it succeeds.
This might have been an alternative solution to the driver dependencies
I was experiencing with GPU switching on the MacBook Pro: The apple-gmux
module needs to be loaded on pre-retinas to switch DDC, and on retinas
the DRM driver for the active GPU needs to have set up the eDP output
so that the inactive GPU can use the pre-calibrated v-swing, pre-emph etc.
I tried something similar to this patch here first, falling back to
1024x786 if the dependencies weren't met, and then tearing down and
reinitializing the fbdev once all prerequisites were fulfilled.
This approach turned out to be too fragile so I settled on -EPROBE_DEFER,
which had the additional advantage of needing much less code.
I'm not sure if a hotplug signal is generated at all on older machines
with a plain vanilla VGA output. If that is not the case, this patch
here will cause a change of behaviour.
It also doesn't solve the issue that a display is unplugged and replaced
with a larger display. The fb resolution will stay the same. Ideally we
should tear down the fbdev if the last display using it is unplugged and
recreate it once something is plugged in again.
Best regards,
Lukas
>
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_fb_helper.c | 36 ++++++++++++++++++++++++++++++++++++
> include/drm/drm_fb_helper.h | 21 +++++++++++++++++++++
> 2 files changed, 57 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 7c2eb75db60f..4f334f9cab28 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -442,6 +442,9 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
> if (!drm_fbdev_emulation)
> return -ENODEV;
>
> + if (fb_helper->deferred_setup)
> + return 0;
> +
> drm_modeset_lock_all(dev);
> ret = restore_fbdev_mode(fb_helper);
>
> @@ -1398,6 +1401,23 @@ unlock:
> }
> EXPORT_SYMBOL(drm_fb_helper_pan_display);
>
> +static bool drm_fb_helper_maybe_connected(struct drm_fb_helper *helper)
> +{
> + bool connected = false;
> + unsigned int i;
> +
> + for (i = 0; i < helper->connector_count; i++) {
> + struct drm_fb_helper_connector *fb = helper->connector_info[i];
> +
> + if (fb->connector->status != connector_status_disconnected) {
> + connected = true;
> + break;
> + }
> + }
> +
> + return connected;
> +}
> +
> /*
> * Allocates the backing storage and sets up the fbdev info structure through
> * the ->fb_probe callback and then registers the fbdev and sets up the panic
> @@ -1499,6 +1519,17 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
> sizes.fb_height = min_t(u32, desired_mode->vdisplay + y, sizes.fb_height);
> }
>
> + /*
> + * If everything's disconnected, there's no use in attempting to set
> + * up fbdev.
> + */
> + if (!drm_fb_helper_maybe_connected(fb_helper)) {
> + DRM_INFO("No outputs connected, deferring setup\n");
> + fb_helper->preferred_bpp = preferred_bpp;
> + fb_helper->deferred_setup = true;
> + return 0;
> + }
> +
> if (crtc_count == 0 || sizes.fb_width == -1 || sizes.fb_height == -1) {
> /* hmm everyone went away - assume VGA cable just fell out
> and will come back later. */
> @@ -1539,6 +1570,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>
> list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list);
>
> + fb_helper->deferred_setup = false;
> return 0;
> }
>
> @@ -2237,6 +2269,10 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
> if (!drm_fbdev_emulation)
> return 0;
>
> + if (fb_helper->deferred_setup)
> + return drm_fb_helper_initial_config(fb_helper,
> + fb_helper->preferred_bpp);
> +
> mutex_lock(&fb_helper->dev->mode_config.mutex);
> if (!fb_helper->fb || !drm_fb_helper_is_bound(fb_helper)) {
> fb_helper->delayed_hotplug = true;
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 5b4aa35026a3..25446690b2c1 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -214,6 +214,27 @@ struct drm_fb_helper {
> bool delayed_hotplug;
>
> /**
> + * @deferred_setup:
> + *
> + * If no outputs are connected (disconnected or unknown) the FB helper
> + * code will defer setup until at least one of the outputs shows up.
> + * This field keeps track of the status so that setup can be retried
> + * at every hotplug event until it succeeds eventually.
> + */
> + bool deferred_setup;
> +
> + /**
> + * @preferred_bpp:
> + *
> + * Temporary storage for the driver's preferred BPP setting passed to
> + * FB helper initialization. This needs to be tracked so that deferred
> + * FB helper setup can pass this on.
> + *
> + * See also: @deferred_setup
> + */
> + int preferred_bpp;
> +
> + /**
> * @atomic:
> *
> * Use atomic updates for restore_fbdev_mode(), etc. This defaults to
> --
> 2.8.3
>
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