kernel/include/drm/drm_panel.h, branch linux-6.18.y

drm/panel: Allow powering on panel follower after panel is enabled

2025-08-25T16:17:49Z

Some touch controllers have to be powered on after the panel's backlight is enabled. To support these controllers, introduce .panel_enabled() and .panel_disabling() to panel_follower_funcs and use them to power on the device after the panel and its backlight are enabled. Signed-off-by: Pin-yen Lin Reviewed-by: Douglas Anderson Signed-off-by: Douglas Anderson Link: https://lore.kernel.org/r/20250818115015.2909525-1-treapking@chromium.org

drm/panel: make prepare/enable and disable/unprepare calls return void

2025-04-22T13:49:11Z

Now there are no users of the return value of the drm_panel_prepare(), drm_panel_unprepare(), drm_panel_enable() and drm_panel_disable() calls. Usually these calls are performed from the atomic callbacks, where it is impossible to return an error. Stop returning error codes and return void instead. Reviewed-by: Neil Armstrong Link: https://lore.kernel.org/r/20250401-panel-return-void-v1-7-93e1be33dc8d@oss.qualcomm.com Signed-off-by: Dmitry Baryshkov

drm/panel: Add refcount support

2025-04-01T14:58:04Z

Allocate panel via reference counting. Add _get() and _put() helper functions to ensure panel allocations are refcounted. Avoid use after free by ensuring panel pointer is valid and can be usable till the last reference is put. Reviewed-by: Luca Ceresoli Reviewed-by: Maxime Ripard Signed-off-by: Anusha Srivatsa Link: https://lore.kernel.org/r/20250331-b4-panel-refcounting-v4-2-dad50c60c6c9@redhat.com Signed-off-by: Maxime Ripard

drm/panel: Add new helpers for refcounted panel allocatons

2025-04-01T14:58:03Z

Introduce reference counted allocations for panels to avoid use-after-free. The patch adds the macro devm_drm_bridge_alloc() to allocate a new refcounted panel. Followed the documentation for drmm_encoder_alloc() and devm_drm_dev_alloc and other similar implementations for this purpose. Reviewed-by: Maxime Ripard Signed-off-by: Anusha Srivatsa Link: https://lore.kernel.org/r/20250331-b4-panel-refcounting-v4-1-dad50c60c6c9@redhat.com Signed-off-by: Maxime Ripard

drm/panel: remove unnecessary forward declaration

2025-02-10T15:48:41Z

'struct drm_device' is not used at all in this file since commit aa6c43644bc5 ("drm/panel: drop drm_device from drm_panel"). Signed-off-by: Luca Ceresoli Reviewed-by: Douglas Anderson Reviewed-by: Dmitry Baryshkov Signed-off-by: Robert Foss Link: https://patchwork.freedesktop.org/patch/msgid/20250206-drm-cleanups-v1-1-93df60faa756@bootlin.com

drm/panel: Fix kernel-doc typo for `follower_lock`

2023-08-03T08:21:27Z

In the kernel doc for the `follower_lock` member of `struct drm_panel` there was a typo where it was called `followers_lock`. This resulted in a warning when making "htmldocs": ./include/drm/drm_panel.h:270: warning: Function parameter or member 'follower_lock' not described in 'drm_panel' Fix the typo. Fixes: de0874165b83 ("drm/panel: Add a way for other devices to follow panel state") Reported-by: Stephen Rothwell Closes: https://lore.kernel.org/r/20230802142136.0f67b762@canb.auug.org.au Signed-off-by: Douglas Anderson Reviewed-by: Neil Armstrong Signed-off-by: Neil Armstrong Link: https://patchwork.freedesktop.org/patch/msgid/20230802074727.1.I4036706ad5e7f45e80d41b777164258e52079cd8@changeid

drm/panel: Add a way for other devices to follow panel state

2023-08-01T14:38:13Z

These days, it's fairly common to see panels that have touchscreens attached to them. The panel and the touchscreen can somewhat be thought of as totally separate devices and, historically, this is how Linux has treated them. However, treating them as separate isn't necessarily the best way to model the two devices, it was just that there was no better way. Specifically, there is little practical reason to have the touchscreen powered on when the panel is turned off, but if we model the devices separately we have no way to keep the two devices' power states in sync with each other. The issue described above makes it sound as if the problem here is just about efficiency. We're wasting power keeping the touchscreen powered up when the screen is off. While that's true, the problem can go deeper. Specifically, hardware designers see that there's no reason to have the touchscreen on while the screen is off and then build hardware assuming that software would never turn the touchscreen on while the screen is off. In the very simplest case of hardware designs like this, the touchscreen and the panel share some power rails. In most cases, this turns out not to be terrible and is, again, just a little less efficient. Specifically if we tell Linux that the touchscreen and the panel are using the same rails then Linux will keep the rails on when _either_ device is turned on. That ends to work OK-ish, but now if you turn the panel off not only will the touchscreen remain powered, but the power rails for the panel itself won't be switched off, burning extra power. The above two inefficiencies are _extra_ minor when you consider the fact that laptops rarely spend much time with the screen off. The main use case would be when an external screen (and presumably a power supply) is attached. Unfortunately, it gets worse from here. On sc7180-trogdor-homestar, for instance, the display's TCON (timing controller) sometimes crashes if you don't power cycle it whenever you stop and restart the video stream (like during a modeset). The touchscreen keeping the power rails on causes real problems. One proposal in the homestar timeframe was to move the touchscreen to an always-on rail, dedicating the main power rail to the panel. That caused _different_ problems as talked about in commit 557e05fa9fdd ("HID: i2c-hid: goodix: Stop tying the reset line to the regulator"). The end result of all of this was to add an extra regulator to the board, increasing cost. Recently, Cong Yang posted a patch [1] where things are even worse. The panel and touch controller on that system seem even more intimately tied together and really can't be thought of separately. To address this issue, let's start allowing devices to register themselves as "panel followers". These devices will get called after a panel has been powered on and before a panel is powered off. This makes the panel the primary device in charge of the power state, which matches how userspace uses it. The panel follower API should be fairly straightforward to use. The current code assumes that panel followers are using device tree and have a "panel" property pointing to the panel to follow. More flexibility and non-DT implementations could be added as needed. Right now, panel followers can follow the prepare/unprepare functions. There could be arguments made that, instead, they should follow enable/disable. I've chosen prepare/unprepare for now since those functions are guaranteed to power up/power down the panel and it seems better to start the process earlier. A bit of explaining about why this is a roll-your-own API instead of using something more standard: 1. In standard APIs in Linux, parent devices are automatically powered on when a child needs power. Applying that here, it would mean that we'd force the panel on any time someone was listening to the touchscreen. That, unfortunately, would have broken homestar's need (if we hadn't changed the hardware, as per above) where the panel absolutely needs to be able to power cycle itself. While one could argue that homestar is broken hardware and we shouldn't have the API do backflips for it, _officially_ the eDP timing guidelines agree with homestar's needs and the panel power sequencing diagrams show power going off. It's nice to be able to support this. 2. We could, conceibably, try to add a new flag to device_link causing the parent to be in charge of power. Then we could at least use normal pm_runtime APIs. This sounds great, except that we run into problems with initial probe. As talked about in the later patch ("HID: i2c-hid: Support being a panel follower") the initial power on of a panel follower might need to do things (like add sub-devices) that aren't allowed in a runtime_resume function. The above complexities explain why this API isn't using common functions. That being said, this patch is very small and self-contained, so if someone was later able to adapt it to using more common APIs while solving the above issues then that could happen in the future. [1] https://lore.kernel.org/r/20230519032316.3464732-1-yangcong5@huaqin.corp-partner.google.com Reviewed-by: Maxime Ripard Signed-off-by: Douglas Anderson Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.3.Icd5f96342d2242051c754364f4bee13ef2b986d4@changeid

drm/panel: Check for already prepared/enabled in drm_panel

2023-08-01T14:35:36Z

In a whole pile of panel drivers, we have code to make the prepare/unprepare/enable/disable callbacks behave as no-ops if they've already been called. It's silly to have this code duplicated everywhere. Add it to the core instead so that we can eventually delete it from all the drivers. Note: to get some idea of the duplicated code, try: git grep 'if.*>prepared' -- drivers/gpu/drm/panel git grep 'if.*>enabled' -- drivers/gpu/drm/panel NOTE: arguably, the right thing to do here is actually to skip this patch and simply remove all the extra checks from the individual drivers. Perhaps the checks were needed at some point in time in the past but maybe they no longer are? Certainly as we continue transitioning over to "panel_bridge" then we expect there to be much less variety in how these calls are made. When we're called as part of the bridge chain, things should be pretty simple. In fact, there was some discussion in the past about these checks [1], including a discussion about whether the checks were needed and whether the calls ought to be refcounted. At the time, I decided not to mess with it because it felt too risky. Looking closer at it now, I'm fairly certain that nothing in the existing codebase is expecting these calls to be refcounted. The only real question is whether someone is already doing something to ensure prepare()/unprepare() match and enabled()/disable() match. I would say that, even if there is something else ensuring that things match, there's enough complexity that adding an extra bool and an extra double-check here is a good idea. Let's add a drm_warn() to let people know that it's considered a minor error to take advantage of drm_panel's double-checking but we'll still make things work fine. We'll also add an entry to the official DRM todo list to remove the now pointless check from the panels after this patch lands and, eventually, fixup anyone who is triggering the new warning. [1] https://lore.kernel.org/r/20210416153909.v4.27.I502f2a92ddd36c3d28d014dd75e170c2d405a0a5@changeid Acked-by: Neil Armstrong Reviewed-by: Maxime Ripard Signed-off-by: Douglas Anderson Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.2.I59b417d4c29151cc2eff053369ec4822b606f375@changeid

drm/panel: Add prepare_prev_first flag to drm_panel

2022-12-08T08:56:57Z

Mapping to the drm_bridge flag pre_enable_prev_first, add a new flag prepare_prev_first to drm_panel to allow the panel driver to request that the upstream bridge should be pre_enabled before the panel prepare. Signed-off-by: Dave Stevenson Reviewed-by: Dmitry Baryshkov Link: https://lore.kernel.org/r/20221205173328.1395350-6-dave.stevenson@raspberrypi.com Signed-off-by: Maxime Ripard

drm/panel: drop DSC pps pointer

2022-09-18T16:38:06Z

Complete the move of DSC data pointer from struct drm_panel to struct mipi_dsi_device. Signed-off-by: Dmitry Baryshkov Reviewed-by: Abhinav Kumar Patchwork: https://patchwork.freedesktop.org/patch/493309/ Link: https://lore.kernel.org/r/20220711094320.368062-4-dmitry.baryshkov@linaro.org Signed-off-by: Dmitry Baryshkov Signed-off-by: Rob Clark