linux-kernel - Re: [PATCH v2 4/7] HID: i2c-hid: elan: fix reset suspend current leakage

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAD=FV=V59t_tZ9Xk=uhbgOdTRYLKu+kZt8cpaksTkJo+D4yt8Q@mail.gmail.com>
Date: Fri, 10 May 2024 16:36:08 -0700
From: Doug Anderson <dianders@...omium.org>
To: Johan Hovold <johan+linaro@...nel.org>
Cc: Jiri Kosina <jikos@...nel.org>, Benjamin Tissoires <benjamin.tissoires@...hat.com>, 
	Bjorn Andersson <andersson@...nel.org>, Dmitry Torokhov <dmitry.torokhov@...il.com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Linus Walleij <linus.walleij@...aro.org>, 
	linux-input@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org, Steev Klimaszewski <steev@...i.org>
Subject: Re: [PATCH v2 4/7] HID: i2c-hid: elan: fix reset suspend current leakage

Hi,

On Tue, May 7, 2024 at 7:48 AM Johan Hovold <johan+linaro@...nel.org> wrote:
>
> @@ -40,17 +41,17 @@ static int elan_i2c_hid_power_up(struct i2chid_ops *ops)
>                 container_of(ops, struct i2c_hid_of_elan, ops);
>         int ret;
>
> +       gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);

Could probably use a comment above it saying that this is important
when we have "no_reset_on_power_off" and doesn't do anything bad when
we don't so we can just do it unconditionally.


> +
>         if (ihid_elan->vcc33) {
>                 ret = regulator_enable(ihid_elan->vcc33);
>                 if (ret)
> -                       return ret;
> +                       goto err_deassert_reset;
>         }
>
>         ret = regulator_enable(ihid_elan->vccio);
> -       if (ret) {
> -               regulator_disable(ihid_elan->vcc33);
> -               return ret;
> -       }
> +       if (ret)
> +               goto err_disable_vcc33;
>
>         if (ihid_elan->chip_data->post_power_delay_ms)
>                 msleep(ihid_elan->chip_data->post_power_delay_ms);
> @@ -60,6 +61,15 @@ static int elan_i2c_hid_power_up(struct i2chid_ops *ops)
>                 msleep(ihid_elan->chip_data->post_gpio_reset_on_delay_ms);
>
>         return 0;
> +
> +err_disable_vcc33:
> +       if (ihid_elan->vcc33)
> +               regulator_disable(ihid_elan->vcc33);
> +err_deassert_reset:
> +       if (ihid_elan->no_reset_on_power_off)
> +               gpiod_set_value_cansleep(ihid_elan->reset_gpio, 0);

Small nit about the error label: it sounds as if when you go here you
_will_ deassert reset when in actuality you might or might not
(depending on no_reset_on_power_off). Personally I prefer to label
error jumps based on things I've done instead of things that the error
jump needs to do, so you could call them "err_enabled_vcc33" and
"err_asserted_reset"...

I don't feel that strongly about it, though, so if you love the label
you have then no need to change it.


> @@ -67,7 +77,14 @@ static void elan_i2c_hid_power_down(struct i2chid_ops *ops)
>         struct i2c_hid_of_elan *ihid_elan =
>                 container_of(ops, struct i2c_hid_of_elan, ops);
>
> -       gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);
> +       /*
> +        * Do not assert reset when the hardware allows for it to remain
> +        * deasserted regardless of the state of the (shared) power supply to
> +        * avoid wasting power when the supply is left on.
> +        */
> +       if (!ihid_elan->no_reset_on_power_off)
> +               gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);
> +
>         if (ihid_elan->chip_data->post_gpio_reset_off_delay_ms)
>                 msleep(ihid_elan->chip_data->post_gpio_reset_off_delay_ms);

Shouldn't  the above two lines be inside the "if
(!ihid_elan->no_reset_on_power_off)" test? If you're not setting the
reset GPIO then you don't need to do the delay, right?


> @@ -79,6 +96,7 @@ static void elan_i2c_hid_power_down(struct i2chid_ops *ops)
>  static int i2c_hid_of_elan_probe(struct i2c_client *client)
>  {
>         struct i2c_hid_of_elan *ihid_elan;
> +       int ret;
>
>         ihid_elan = devm_kzalloc(&client->dev, sizeof(*ihid_elan), GFP_KERNEL);
>         if (!ihid_elan)
> @@ -93,21 +111,38 @@ static int i2c_hid_of_elan_probe(struct i2c_client *client)
>         if (IS_ERR(ihid_elan->reset_gpio))
>                 return PTR_ERR(ihid_elan->reset_gpio);
>
> +       ihid_elan->no_reset_on_power_off = of_property_read_bool(client->dev.of_node,
> +                                               "no-reset-on-power-off");

Personally, I'd rather you query for the property before you request
the GPIO and then request the GPIO in the "powered off" state just to
keep everything in the most consistent state possible.


-Doug