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

[Krzysztof Kozlowski]

On 26/06/2026 04:15, Sunyun Yang wrote:
> Krzysztof Kozlowski <krzk@xxxxxxxxxx> 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@xxxxxxxxxxx> 于2026年6月25日周四 21:26写道：
>>>>
>>>> Krzysztof Kozlowski <krzk@xxxxxxxxxx> 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@xxxxxxxxxx> 于2026年6月25日周四 20:54写道：
>>>>>>>
>>>>>>> On 08/05/2026 15:40, syyang@xxxxxxxxxxx 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?

DT has nothing to do here. 1 is assert, 0 is de-assert. Your code does
things opposite to any logic, because you finish function with reset
asserted.


Best regards,
Krzysztof