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Date:   Sun, 23 Apr 2023 22:38:29 -0500
From:   Jeff LaBundy <jeff@labundy.com>
To:     Fei Shao <fshao@chromium.org>
Cc:     Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Douglas Anderson <dianders@chromium.org>,
        Rob Herring <robh+dt@kernel.org>,
        linux-mediatek <linux-mediatek@lists.infradead.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Jiri Kosina <jikos@kernel.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        Stephen Kitt <steve@sk2.org>, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] HID: i2c-hid: goodix: Add support for
 powered-in-suspend property
Message-ID: <ZEX5tc2LSZoVswc2@nixie71>
References: <20230418124953.3170028-1-fshao@chromium.org>
 <20230418124953.3170028-3-fshao@chromium.org>
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Hi Fei,

On Tue, Apr 18, 2023 at 08:49:52PM +0800, Fei Shao wrote:
> In the beginning, commit 18eeef46d359 ("HID: i2c-hid: goodix: Tie the
> reset line to true state of the regulator") introduced a change to tie
> the reset line of the Goodix touchscreen to the state of the regulator
> to fix a power leakage issue in suspend.
> 
> After some time, the change was deemed unnecessary and was reverted in
> commit 557e05fa9fdd ("HID: i2c-hid: goodix: Stop tying the reset line to
> the regulator") due to difficulties in managing regulator notifiers for
> designs like Evoker, which provides a second power rail to touchscreen.
> 
> However, the revert caused a power regression on another Chromebook
> device Steelix in the field, which has a dedicated always-on regulator
> for touchscreen and was covered by the workaround in the first commit.
> 
> To address both cases, this patch adds the support for the
> `powered-in-suspend` property in the driver that allows the driver to
> determine whether the touchscreen is still powered in suspend, and
> handle the reset GPIO accordingly as below:
> - When set to true, the driver does not assert the reset GPIO in power
>   down. To ensure a clean start and the consistent behavior, it does the
>   assertion in power up instead.
>   This is for designs with a dedicated always-on regulator.
> - When set to false, the driver uses the original control flow and
>   asserts GPIO and disable regulators normally.
>   This is for the two-regulator and shared-regulator designs.
> 
> Signed-off-by: Fei Shao <fshao@chromium.org>
> 
> ---
> 
>  drivers/hid/i2c-hid/i2c-hid-of-goodix.c | 46 +++++++++++++++++++++----
>  1 file changed, 39 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/hid/i2c-hid/i2c-hid-of-goodix.c b/drivers/hid/i2c-hid/i2c-hid-of-goodix.c
> index 0060e3dcd775..b438db8ca6f4 100644
> --- a/drivers/hid/i2c-hid/i2c-hid-of-goodix.c
> +++ b/drivers/hid/i2c-hid/i2c-hid-of-goodix.c
> @@ -28,6 +28,7 @@ struct i2c_hid_of_goodix {
>  	struct regulator *vdd;
>  	struct regulator *vddio;
>  	struct gpio_desc *reset_gpio;
> +	bool powered_in_suspend;
>  	const struct goodix_i2c_hid_timing_data *timings;
>  };
>  
> @@ -37,13 +38,34 @@ static int goodix_i2c_hid_power_up(struct i2chid_ops *ops)
>  		container_of(ops, struct i2c_hid_of_goodix, ops);
>  	int ret;
>  
> -	ret = regulator_enable(ihid_goodix->vdd);
> -	if (ret)
> -		return ret;
> -
> -	ret = regulator_enable(ihid_goodix->vddio);
> -	if (ret)
> -		return ret;
> +	/*
> +	 * This is to ensure that the reset GPIO will be asserted and the
> +	 * regulators will be enabled for all cases.
> +	 */
> +	if (ihid_goodix->powered_in_suspend) {
> +		/*
> +		 * This is not mandatory, but we assert reset here (instead of
> +		 * in power-down) to ensure that the device will have a clean
> +		 * state later on just like the normal scenarios would have.
> +		 *
> +		 * Also, since the regulators were not disabled in power-down,
> +		 * we don't need to enable them here.
> +		 */
> +		gpiod_set_value_cansleep(ihid_goodix->reset_gpio, 1);
> +	} else {
> +		/*
> +		 * In this case, the reset is already asserted (either in
> +		 * probe or power-down).
> +		 * All we need is to enable the regulators.
> +		 */
> +		ret = regulator_enable(ihid_goodix->vdd);
> +		if (ret)
> +			return ret;
> +
> +		ret = regulator_enable(ihid_goodix->vddio);
> +		if (ret)
> +			return ret;
> +	}

Please let me know in case I have misunderstood, but I don't see a need
to change the regulator_enable/disable() logic if this property is set.
If the regulators are truly always-on, the regulator core already knows
what to do and we should not duplicate that logic here.

Based on the alleged silicon erratum discussed in patch [1/2], it seems
we only want to control the behavior of the reset GPIO. Therefore, only
the calls to gpiod_set_value_cansleep() should be affected and the name
of the property updated to reflect what it's actually doing.

>  
>  	if (ihid_goodix->timings->post_power_delay_ms)
>  		msleep(ihid_goodix->timings->post_power_delay_ms);
> @@ -60,6 +82,13 @@ static void goodix_i2c_hid_power_down(struct i2chid_ops *ops)
>  	struct i2c_hid_of_goodix *ihid_goodix =
>  		container_of(ops, struct i2c_hid_of_goodix, ops);
>  
> +	/*
> +	 * Don't assert reset GPIO or disable regulators if we're keeping the
> +	 * device powered in suspend.
> +	 */
> +	if (ihid_goodix->powered_in_suspend)
> +		return;
> +
>  	gpiod_set_value_cansleep(ihid_goodix->reset_gpio, 1);
>  	regulator_disable(ihid_goodix->vddio);
>  	regulator_disable(ihid_goodix->vdd);
> @@ -91,6 +120,9 @@ static int i2c_hid_of_goodix_probe(struct i2c_client *client)
>  	if (IS_ERR(ihid_goodix->vddio))
>  		return PTR_ERR(ihid_goodix->vddio);
>  
> +	ihid_goodix->powered_in_suspend =
> +		of_property_read_bool(client->dev.of_node, "powered-in-suspend");
> +
>  	ihid_goodix->timings = device_get_match_data(&client->dev);
>  
>  	return i2c_hid_core_probe(client, &ihid_goodix->ops, 0x0001, 0);
> -- 
> 2.40.0.634.g4ca3ef3211-goog
> 

Kind regards,
Jeff LaBundy