On Jul 25 2023, Douglas Anderson wrote:
> 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.
>
> Signed-off-by: Douglas Anderson <[email protected]>
> ---
>
> Changes in v3:
> - Add "depends on DRM || !DRM" to Kconfig to avoid randconfig error.
> - Split more of the panel follower code out of the core.
>
> Changes in v2:
> - i2c_hid_core_panel_prepared() and ..._unpreparing() are now static.
>
> drivers/hid/i2c-hid/Kconfig | 2 +
> drivers/hid/i2c-hid/i2c-hid-core.c | 82 +++++++++++++++++++++++++++++-
> 2 files changed, 82 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hid/i2c-hid/Kconfig b/drivers/hid/i2c-hid/Kconfig
> index 3be17109301a..2bdb55203104 100644
> --- a/drivers/hid/i2c-hid/Kconfig
> +++ b/drivers/hid/i2c-hid/Kconfig
> @@ -70,5 +70,7 @@ config I2C_HID_OF_GOODIX
>
> config I2C_HID_CORE
> tristate
> + # We need to call into panel code so if DRM=m, this can't be 'y'
> + depends on DRM || !DRM
> endif
>
> diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c
> b/drivers/hid/i2c-hid/i2c-hid-core.c
> index fa8a1ca43d7f..fa6d1f624342 100644
> --- a/drivers/hid/i2c-hid/i2c-hid-core.c
> +++ b/drivers/hid/i2c-hid/i2c-hid-core.c
> @@ -38,6 +38,8 @@
> #include <linux/mutex.h>
> #include <asm/unaligned.h>
>
> +#include <drm/drm_panel.h>
> +
> #include "../hid-ids.h"
> #include "i2c-hid.h"
>
> @@ -107,6 +109,8 @@ struct i2c_hid {
> struct mutex reset_lock;
>
> struct i2chid_ops *ops;
> + struct drm_panel_follower panel_follower;
> + bool is_panel_follower;
> };
>
> static const struct i2c_hid_quirks {
> @@ -1058,6 +1062,59 @@ static int i2c_hid_core_initial_power_up(struct
> i2c_hid *ihid)
> return ret;
> }
>
> +static int i2c_hid_core_panel_prepared(struct drm_panel_follower *follower)
> +{
> + struct i2c_hid *ihid = container_of(follower, struct i2c_hid,
> panel_follower);
> + struct hid_device *hid = ihid->hid;
> +
> + /*
> + * hid->version is set on the first power up. If it's still zero then
> + * this is the first power on so we should perform initial power up
> + * steps.
> + */
> + if (!hid->version)
> + return i2c_hid_core_initial_power_up(ihid);
> +
> + return i2c_hid_core_resume(ihid);
> +}
> +
> +static int i2c_hid_core_panel_unpreparing(struct drm_panel_follower
> *follower)
> +{
> + struct i2c_hid *ihid = container_of(follower, struct i2c_hid,
> panel_follower);
> +
> + return i2c_hid_core_suspend(ihid);
> +}
> +
> +static const struct drm_panel_follower_funcs
> i2c_hid_core_panel_follower_funcs = {
> + .panel_prepared = i2c_hid_core_panel_prepared,
> + .panel_unpreparing = i2c_hid_core_panel_unpreparing,
> +};
> +
> +static int i2c_hid_core_register_panel_follower(struct i2c_hid *ihid)
> +{
> + struct device *dev = &ihid->client->dev;
> + int ret;
> +
> + ihid->is_panel_follower = true;
> + ihid->panel_follower.funcs = &i2c_hid_core_panel_follower_funcs;
> +
> + /*
> + * If we're not in control of our own power up/power down then we can't
> + * do the logic to manage wakeups. Give a warning if a user thought
> + * that was possible then force the capability off.
> + */
> + if (device_can_wakeup(dev)) {
> + dev_warn(dev, "Can't wakeup if following panel\n");
> + device_set_wakeup_capable(dev, false);
> + }
> +
> + ret = drm_panel_add_follower(dev, &ihid->panel_follower);
> + if (ret)
> + return ret;
> +
> + return 0;
> +}
> +
> int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
> u16 hid_descriptor_address, u32 quirks)
> {
> @@ -1119,7 +1176,15 @@ int i2c_hid_core_probe(struct i2c_client *client,
> struct i2chid_ops *ops,
> hid->bus = BUS_I2C;
> hid->initial_quirks = quirks;
>
> - ret = i2c_hid_core_initial_power_up(ihid);
> + /*
> + * If we're a panel follower, we'll register and do our initial power
> + * up when the panel turns on; otherwise we do it right away.
> + */
> + if (drm_is_panel_follower(&client->dev))
> + ret = i2c_hid_core_register_panel_follower(ihid);
> + else
> + ret = i2c_hid_core_initial_power_up(ihid);
nitpicks, but I'm not sure I'm a big fan of having
"if (drm_is_panel_follower(&client->dev))" sprinkled everywhere in the
generic probe/resume/suspend code.
Would it be OK to define a `static int
__do_i2c_hid_core_initial_power_up(struct i2c_hid *ihid)`
that would do the actual powering up, and have
i2c_hid_core_initial_power_up() doing the test if we are a panel
follower?
The i2c_hid_core_panel_* will need to be updated to use the `__do_`
prefixed functions.
> +
> if (ret)
> goto err_mem_free;
>
> @@ -1143,7 +1208,14 @@ void i2c_hid_core_remove(struct i2c_client *client)
> struct i2c_hid *ihid = i2c_get_clientdata(client);
> struct hid_device *hid;
>
> - i2c_hid_core_power_down(ihid);
> + /*
> + * If we're a follower, the act of unfollowing will cause us to be
> + * powered down. Otherwise we need to manually do it.
> + */
> + if (ihid->is_panel_follower)
> + drm_panel_remove_follower(&ihid->panel_follower);
That part is concerning, as we are now calling hid_drv->suspend() when removing
the device. It might or not have an impact (I'm not sure of it), but we
are effectively changing the path of commands sent to the device.
hid-multitouch might call a feature in ->suspend, but the remove makes
that the physical is actually disconnected, so the function will fail,
and I'm not sure what is happening then.
> + else
> + i2c_hid_core_power_down(ihid);
Same here, I *think* it would be best to have the `if (ihid->is_panel_follower)`
test in i2c_hid_core_power_down() (and have a separate
_do_i2c_hid_core_power_down()).
>
> hid = ihid->hid;
> hid_destroy_device(hid);
> @@ -1171,6 +1243,9 @@ static int i2c_hid_core_pm_suspend(struct device *dev)
> struct i2c_client *client = to_i2c_client(dev);
> struct i2c_hid *ihid = i2c_get_clientdata(client);
>
> + if (ihid->is_panel_follower)
> + return 0;
Not sure we need to split that one with _do_ prefix, it's already split
:)
> +
> return i2c_hid_core_suspend(ihid);
> }
>
> @@ -1179,6 +1254,9 @@ static int i2c_hid_core_pm_resume(struct device *dev)
> struct i2c_client *client = to_i2c_client(dev);
> struct i2c_hid *ihid = i2c_get_clientdata(client);
>
> + if (ihid->is_panel_follower)
> + return 0;
Same here, no need to split.
> +
> return i2c_hid_core_resume(ihid);
> }
>
> --
> 2.41.0.487.g6d72f3e995-goog
>
Cheers,
Benjamin
