Re: [PATCH v6 2/2] drm/bridge: Add Lontium LT9611C(EX/UXD) MIPI DSI to HDMI driver

[Maxime Ripard <mripard@kernel.org>]

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On Fri, Jun 26, 2026 at 04:13:18PM +0800, Sunyun Yang wrote:
> Maxime Ripard <mripard@kernel.org> 于2026年6月26日周五 15:49写道：
> >
> > On Fri, Jun 26, 2026 at 10:15:03AM +0800, Sunyun Yang wrote:
> > > Krzysztof Kozlowski <krzk@kernel.org> 于2026年6月25日周四 21:51写道：
> > > >
> > > > On 25/06/2026 15:40, Sunyun Yang wrote:
> > > > > Sunyun Yang <syyang@lontium.com> 于2026年6月25日周四 21:26写道：
> > > > >>
> > > > >> Krzysztof Kozlowski <krzk@kernel.org> 于2026年6月25日周四 21:17写道：
> > > > >>>
> > > > >>> On 25/06/2026 15:14, Sunyun Yang wrote:
> > > > >>>> Krzysztof Kozlowski <krzk@kernel.org> 于2026年6月25日周四 20:54写道：
> > > > >>>>>
> > > > >>>>> On 08/05/2026 15:40, syyang@lontium.com wrote:
> > > > >>>>>> +
> > > > >>>>>> +static void lt9611c_reset(struct lt9611c *lt9611c)
> > > > >>>>>> +{
> > > > >>>>>> +     gpiod_set_value_cansleep(lt9611c->reset_gpio, 1);
> > > > >>>>>> +     msleep(20);
> > > > >>>>>> +
> > > > >>>>>> +     gpiod_set_value_cansleep(lt9611c->reset_gpio, 0);
> > > > >>>>>> +     msleep(20);
> > > > >>>>>> +
> > > > >>>>>> +     gpiod_set_value_cansleep(lt9611c->reset_gpio, 1);
> > > > >>>>>
> > > > >>>>> This is just plain wrong. Why do you assert, then de-assert and then
> > > > >>>>> finally assert AGAIN the reset leaving the device in powerdown stage?
> > > > >>>>>
> > > > >>>> I am using software to emulate the hardware RESET button on our EVB.
> > > > >>>> When the hardware RESET button is pressed while our chip is running,
> > > > >>>> the signal level changes from HIGH to LOW and then back to HIGH.
> > > > >>>>
> > > > >>>> Of course, we can also use the following:
> > > > >>>> static void lt9611c_reset(struct lt9611c *lt9611c)
> > > > >>>> {
> > > > >>>>     gpiod_set_value_cansleep(lt9611c->reset_gpio, 0);
> > > > >>>>     msleep(50);
> > > > >>>>     gpiod_set_value_cansleep(lt9611c->reset_gpio, 1);
> > > > >>>>     msleep(20);
> > > > >>>> }
> > > > >>>
> > > > >>> Makes no sense either and you just did not get the point and did not
> > > > >>> answer my question. I asked WHY you leave asserted. Answer "we emulate"
> > > > >>> is just plain wrong.
> > > > >>>
> > > > >>> So again please answer:
> > > > >>>
> > > > >>> Why do you leave device with reset asserted?
> > > > >>>
> > > > >>
> > > > >>  devicetree:   reset-gpios = <&tlmm 128 GPIO_ACTIVE_HIGH>;
> > > > >>
> > > > >> GPIO_ACTIVE_HIGH:
> > > > >>
> > > > >> gpiod_set_value_cansleep(lt9611c->reset_gpio, 0);   ------   reset pin
> > > > >> is Low level : Clear the register configuration in the chip to stop
> > > > >> the chip from working.
> > > > >>
> > > > >> gpiod_set_value_cansleep(lt9611c->reset_gpio, 1);   ------  reset pin
> > > > >> is high level:  The chip resumes operation.
> > > > >>
> > > > >>
> > > > >
> > > > > Our purpose is: pull the level low to clear the register configuration
> > > > > in the chip, and then pull it high to allow the MCU inside the chip to
> > > > > re‑initialize the registers.
> > > >
> > > >
> > > > And you do completely opposite... so that confirms your code is just wrong.
> > > >
> > >
> > > The lontium-lt9611.yaml uses GPIO_ACTIVE_HIGH. I am just following the
> > > rule of this device tree. If I modify the device tree to use
> > > GPIO_ACTIVE_LOW,
> > > and use the following code in my driver, then my driver would be correct.
> > > However, would the existing kernel drivers lontium-lt9611uxc.c and
> > > lontium-lt9611.c be affected?
> >
> > It might, but then it's a DT problem. The GPIO API for drivers always
> > considers the logical state of a GPIO, so if you need to assert a
> > signal, you'll always need to set 1. That's what Krzysztof was trying to
> > explain.
> >
> > The DT will provide with GPIO_ACTIVE_* how that logical state translates
> > to a physical GPIO state.
> >
> > If the DT says that this particular GPIO is active-high, then it means
> > that we need to set the GPIO to 1 to assert reset. Now of course, it
> > might not make sense for the controller itself, but it might for the
> > board if there's a GPIO inverter in the middle for example.
> >
> > Anyway, in the case you're raising, the issue definitely lies in the DT,
> > and that's what would need to be fixed.
> >
> > I also wouldn't be too concerned about lontium-lt9611.yaml, it's just an
> > example.
> >
> > Maxime
> 
> thanks Maxime, I will modify this code in the next version of the
> driver, and I hope you can accept these changes.
> 
> Maxime:
> I have another question I would like to ask you
> regarding sashiko-bot@kernel.org. Since sashiko-bot sometimes has
> opinions that differ from yours, whose advice should I follow?
> 
> If I do not adopt sashiko-bot's suggestions, will my patches still be
> accepted into the upstream Linux kernel?

I can't give a blanket answer. It depends on what you ignore exactly.

Maxime

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