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  1. 04 Aug, 2023 12 commits
  3. 03 Aug, 2023 15 commits
  5. 02 Aug, 2023 4 commits
  7. 01 Aug, 2023 9 commits
    • Douglas Anderson's avatar
      HID: i2c-hid: Do panel follower work on the system_wq · 76edfcf4
      Douglas Anderson authored 
      Turning on an i2c-hid device can be a slow process. This is why
i2c-hid devices use PROBE_PREFER_ASYNCHRONOUS. Unfortunately, when
we're a panel follower the i2c-hid power up sequence now blocks the
power on of the panel. Let's fix that by scheduling the work on the
system_wq.
Reviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Reviewed-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Acked-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.10.I962bb462ede779005341c49320740ed95810021d@changeid
      76edfcf4
    • Douglas Anderson's avatar
      HID: i2c-hid: Support being a panel follower · 96a37bfd
      Douglas Anderson authored 
      As talked about in the patch ("drm/panel: Add a way for other devices
to follow panel state"), we really want to keep the power states of a
touchscreen and the panel it's attached to in sync with each other. In
that spirit, add support to i2c-hid to be a panel follower. This will
let the i2c-hid driver get informed when the panel is powered on and
off. From there we can match the i2c-hid device's power state to that
of the panel.

NOTE: this patch specifically _doesn't_ use pm_runtime to keep track
of / manage the power state of the i2c-hid device, even though my
first instinct said that would be the way to go. Specific problems
with using pm_runtime():
* The initial power up couldn't happen in a runtime resume function
  since it create sub-devices and, apparently, that's not good to do
  in your resume function.
* Managing our power state with pm_runtime meant fighting to make the
  right thing happen at system suspend to prevent the system from
  trying to resume us only to suspend us again. While this might be
  able to be solved, it added complexity.
Overall the code without pm_runtime() ended up being smaller and
easier to understand.
Reviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Reviewed-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Acked-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.9.Ib1a98309c455cd7e26b931c69993d4fba33bbe15@changeid
      96a37bfd
    • Douglas Anderson's avatar
      HID: i2c-hid: Suspend i2c-hid devices in remove · 5f8838e9
      Douglas Anderson authored 
      In the i2c-hid remove() function we currently try to power off,
depopulate our child device, and free our resources. That's OK, but...

* If the i2c-hid device is on a power rail that can't turn off (either
  an always-on or a shared power rail) we won't try to put the device
  in a low power state during remove(). This probably doesn't matter
  for very many devices but it could be nice in some instances.

* If the i2c-hid device somehow manages to generate an interrupt after
  we tried to power off it is conceivable that the interrupt could
  arrive during or after the call to hid_destroy_device() but before
  the call to free_irq(). That could cause a crash since our IRQ
  handler isn't expecting it. One could imagine this happening in
  the case where we couldn't turn off (see the previous bullet) or,
  possibly, if the interrupt line could glitch shortly after the
  device powered off.

Let's call the suspend code during remove to avoid these issues. That
will put the device into a low power state and also disable
interrupts.

Technically, one could consider this a "fix" of commit 4a200c3b
("HID: i2c-hid: introduce HID over i2c specification implementation").
However, since the above bullet points are more theoretical than
problems seen on real systems and since the remove() of an i2c-hid
touchscreen isn't terribly likely to be called in production, it's
probably not worth the bother of trying to backport it.
Reviewed-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Acked-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.8.Ic3ecad4a825905f4e4ce2a772b17f3c9cb2d60a2@changeid
      5f8838e9
    • Douglas Anderson's avatar
      HID: i2c-hid: Make suspend and resume into helper functions · d93d2847
      Douglas Anderson authored 
      In a future patch we'd like to be able to call the current i2c-hid
suspend and resume functions from times other than system
suspend. Move the functions higher up in the file and have them take a
"struct i2c_hid" to make this simpler. We'll then add tiny wrappers of
the functions for use with system suspend.

This change is expected to have no functional effect.
Reviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Reviewed-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Acked-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.7.I5c9894789b8b02f029bf266ae9b4f43c7907a173@changeid
      d93d2847
    • Douglas Anderson's avatar
      HID: i2c-hid: Rearrange probe() to power things up later · 675cd877
      Douglas Anderson authored 
      In a future patch, we want to change i2c-hid not to necessarily power
up the touchscreen during probe. In preparation for that, rearrange
the probe function so that we put as much stuff _before_ powering up
the device as possible.

This change is expected to have no functional effect.
Reviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Reviewed-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Acked-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.6.Ifcc9b0a44895d164788966f9b9511fe094ca8cf9@changeid
      675cd877
    • Douglas Anderson's avatar
      HID: i2c-hid: Switch to SYSTEM_SLEEP_PM_OPS() · a889ee12
      Douglas Anderson authored 
      The SYSTEM_SLEEP_PM_OPS() allows us to get rid of '#ifdef
CONFIG_PM_SLEEP', as talked about in commit 1a3c7bb0 ("PM: core:
Add new *_PM_OPS macros, deprecate old ones").

This change is expected to have no functional effect.
Reviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Reviewed-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Acked-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.5.Ib2a2865bd3c0b068432259dfc7d76cebcbb512be@changeid
      a889ee12
    • Douglas Anderson's avatar
      of: property: fw_devlink: Add a devlink for panel followers · fbf0ea2d
      Douglas Anderson authored 
      Inform fw_devlink of the fact that a panel follower (like a
touchscreen) is effectively a consumer of the panel from the purposes
of fw_devlink.

NOTE: this patch isn't required for correctness but instead optimizes
probe order / helps avoid deferrals.
Acked-by: default avatarRob Herring <robh@kernel.org>
Reviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.4.Ibf8e1342b5b7906279db2365aca45e6253857bb3@changeid
      fbf0ea2d
    • Douglas Anderson's avatar
      drm/panel: Add a way for other devices to follow panel state · de087416
      Douglas Anderson authored 
      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 557e05fa ("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.comReviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.3.Icd5f96342d2242051c754364f4bee13ef2b986d4@changeid
      de087416
    • Douglas Anderson's avatar
      drm/panel: Check for already prepared/enabled in drm_panel · d2aacaf0
      Douglas Anderson authored 
      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@changeidAcked-by: default avatarNeil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.2.I59b417d4c29151cc2eff053369ec4822b606f375@changeid
      d2aacaf0
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