From: Krzysztof Kozlowski <krzk@kernel.org>
To: Johan Hovold <johan@kernel.org>
Cc: Johan Hovold <johan+linaro@kernel.org>,
Jiri Kosina <jikos@kernel.org>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Rob Herring <robh@kernel.org>,
Krzysztof Kozlowski <krzk+dt@kernel.org>,
Conor Dooley <conor+dt@kernel.org>,
Bjorn Andersson <andersson@kernel.org>,
Konrad Dybcio <konrad.dybcio@linaro.org>,
Linus Walleij <linus.walleij@linaro.org>,
Douglas Anderson <dianders@chromium.org>,
linux-input@vger.kernel.org, devicetree@vger.kernel.org,
linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/6] dt-bindings: HID: i2c-hid: elan: add 'no-reset-on-power-off' property
Date: Fri, 3 May 2024 11:11:16 +0200 [thread overview]
Message-ID: <48ec0bb5-a06e-4f18-97c3-1370b7facea4@kernel.org> (raw)
In-Reply-To: <ZjNjMBNMegmTgN5B@hovoldconsulting.com>
On 02/05/2024 11:56, Johan Hovold wrote:
> Hi Krzysztof,
>
> and sorry about the late reply. Got side-tracked.
>
> On Thu, Apr 25, 2024 at 11:39:24AM +0200, Krzysztof Kozlowski wrote:
>> On 24/04/2024 09:34, Johan Hovold wrote:
>>> On Tue, Apr 23, 2024 at 06:29:44PM +0200, Krzysztof Kozlowski wrote:
>>>> On 23/04/2024 15:46, Johan Hovold wrote:
>>>>> When the power supply is shared with other peripherals the reset line
>>>>> can be wired in such a way that it can remain deasserted regardless of
>>>>> whether the supply is on or not.
>
>>>>> This is important as it can be used to avoid holding the controller in
>>>>> reset for extended periods of time when it remains powered, something
>>>>> which can lead to increased power consumption. Leaving reset deasserted
>>>>> also avoids leaking current through the reset circuitry pull-up
>>>>> resistors.
>>>>>
>>>>> Add a new 'no-reset-on-power-off' devicetree property which can be used
>>>>> by the OS to determine when reset needs to be asserted on power down.
>>>>>
>>>>> Note that this property can also be used when the supply cannot be
>>>>> turned off by the OS at all.
>>>
>>>>> reset-gpios:
>>>>> description: Reset GPIO; not all touchscreens using eKTH6915 hook this up.
>>>>>
>>>>> + no-reset-on-power-off:
>
>>>> Anyway, the property sounds like what the OS should be doing, which is
>>>> not what we want. You basically instruct driver what to do. We want a
>>>> described hardware configuration or hardware specifics.
>>>
>>> Right, and this was why I at first rejected a property name like this in
>>> favour of 'reset-pulled-to-supply' in my first draft. That name
>>> obviously does not work as the 'supply' suffix is already claimed, but I
>>> also realised that it doesn't really describe the hardware property that
>>> allows the reset line to remain asserted.
>>>
>>> The key feature in this hardware design is that the reset line will not
>>> just be pulled to the supply voltage (what other voltage would it be
>>> pulled to), but that it is also pulled to ground when the supply is
>>> disabled.
>>
>> OK, if the property was specific to the hardware, then I would propose
>> something more hardware-related, e.g. "reset-supply-tied". However :
>>
>>> Rather than trying to encode this in the property name, I settled on the
>>> descriptive 'no-reset-on-power-off' after the seeing the prior art in
>>> 'goodix,no-reset-during-suspend' property. The latter is too specific
>>> and encodes policy, but the former could still be considered hardware
>>> description and would also apply to other designs which have the
>>> property that the reset line should be left deasserted.
>>>
>>> One such example is when the supply can not be disabled at all (e.g. the
>>> Goodix case), but I can imagine there being more than one way to design
>>> such reset circuits.
>>
>> It seems it is common problem. LEDs have property
>> "retain-state-shutdown", to indicate that during system shutdown we
>> should not touch them (like power off). Would some variant be applicable
>> here? First, do we talk here about power off like system shutdown or
>> runtime PM, thus suspend?
>
> A name like 'retain-state-shutdown' would also be too specific as what
> I'm describing here is that the reset line should be (or can be) left
> deasserted whenever the OS wants to power off the device.
I don't think it is more specific than yours. It is actually more
generic. First, shutdown=poweroff, so that part is the same.
retain-state means keep things enabled, asserted, deasserted, etc, so
multiple cases. Your wording is specific - only one state is kept during
power off: reset deassert.
Best regards,
Krzysztof
next prev parent reply other threads:[~2024-05-03 9:11 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-23 13:46 [PATCH 0/6] HID/arm64: dts: qcom: sc8280xp-x13s: fix touchscreen power on Johan Hovold
2024-04-23 13:46 ` [PATCH 1/6] dt-bindings: HID: i2c-hid: add dedicated Ilitek ILI2901 schema Johan Hovold
2024-04-23 16:23 ` Krzysztof Kozlowski
2024-04-23 13:46 ` [PATCH 2/6] dt-bindings: HID: i2c-hid: elan: add Elan eKTH5015M Johan Hovold
2024-04-23 16:24 ` Krzysztof Kozlowski
2024-04-24 7:03 ` Johan Hovold
2024-04-24 8:32 ` Krzysztof Kozlowski
2024-04-23 13:46 ` [PATCH 3/6] dt-bindings: HID: i2c-hid: elan: add 'no-reset-on-power-off' property Johan Hovold
2024-04-23 16:29 ` Krzysztof Kozlowski
2024-04-24 7:34 ` Johan Hovold
2024-04-25 9:39 ` Krzysztof Kozlowski
2024-05-02 9:56 ` Johan Hovold
2024-05-03 9:11 ` Krzysztof Kozlowski [this message]
2024-05-03 9:25 ` Johan Hovold
2024-05-03 7:40 ` Linus Walleij
2024-05-03 8:47 ` Johan Hovold
2024-05-06 6:29 ` Linus Walleij
2024-05-07 14:30 ` Johan Hovold
2024-04-23 13:46 ` [PATCH 4/6] HID: i2c-hid: elan: fix reset suspend current leakage Johan Hovold
2024-04-23 20:37 ` Doug Anderson
2024-04-24 10:56 ` Johan Hovold
2024-04-24 16:24 ` Doug Anderson
2024-04-26 9:29 ` Johan Hovold
2024-04-23 13:46 ` [PATCH 5/6] arm64: dts: qcom: sc8280xp-x13s: fix touchscreen power on Johan Hovold
2024-04-23 13:46 ` [PATCH 6/6] arm64: dts: qcom: sc8280xp-crd: use external pull up for touch reset Johan Hovold
2024-04-23 19:34 ` [PATCH 0/6] HID/arm64: dts: qcom: sc8280xp-x13s: fix touchscreen power on Steev Klimaszewski
2024-04-24 7:38 ` Johan Hovold
2024-04-23 20:36 ` Doug Anderson
2024-04-24 8:50 ` Johan Hovold
2024-04-24 16:24 ` Doug Anderson
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