[PATCH v2 1/2] drm/mipi-dsi: add (LPM) Low Power Mode transfer support

[Inki Dae]

On 2014년 08월 07일 22:17, Thierry Reding wrote:
> On Thu, Aug 07, 2014 at 10:05:44PM +0900, Inki Dae wrote:
>> On 2014년 08월 07일 20:09, Thierry Reding wrote:
>>> On Thu, Aug 07, 2014 at 07:49:03PM +0900, Inki Dae wrote:
>>>> On 2014년 08월 07일 18:09, Thierry Reding wrote:
>>>>> On Thu, Aug 07, 2014 at 04:51:18PM +0900, Inki Dae wrote:
>>>>>> On 2014년 08월 07일 15:58, Thierry Reding wrote:
>>>>>>> On Thu, Aug 07, 2014 at 02:09:19AM +0900, Inki Dae wrote:
>>>>>>>> 2014-08-06 16:43 GMT+09:00 Thierry Reding <thierry.reding at gmail.com>:
>>>>> [...]
>>>>>>>>> As far as I can tell non-continuous mode simply means that the host can
>>>>>>>>> turn off the HS clock after a high-speed transmission. I think Andrzej
>>>>>>>>> mentioned this already in another subthread, but this is an optional
>>>>>>>>> mode that peripherals can support if they have extra circuitry that
>>>>>>>>> provides an internal clock. Peripherals that don't have such circuitry
>>>>>>>>> may rely on the HS clock to perform in between transmissions and
>>>>>>>>> therefore require the HS clock to be always on (continuous mode). That's
>>>>>>>>> what the MIPI_DSI_CLOCK_NON_CONTINUOUS flag is: it advertises that the
>>>>>>>>> peripheral supports non-continuous mode and therefore the host can turn
>>>>>>>>> the HS clock off after high-speed transmissions.
>>>>>>>>
>>>>>>>> What I don't make sure is this sentence. With
>>>>>>>> MIPI_DSI_CLOCK_NON_CONTIUOUS flag, I guess two possible operations.
>>>>>>>> One is,
>>>>>>>> 1. host controller will generates signals if a bit of a register
>>>>>>>> related to non-contiguous clock mode is set or unset.
>>>>>>>> 2. And then video data is transmitted to panel in HS mode.
>>>>>>>> 3. And then D-PHY detects LP-11 signal (positive and negative lane all
>>>>>>>> are high).
>>>>>>>> 4. And then D-PHY disables HS clock of host controller.
>>>>>>>> 5. At this time, operation mode of host controller becomes LPM.
>>>>>>>>
>>>>>>>> Other is,
>>>>>>>> 1. host controller will generates signals if a bit of a register
>>>>>>>> related to non-contiguous clock mode is set or unset.
>>>>>>>> 2. And then D-PHY detects LP-11 signal (positive and negative lane all
>>>>>>>> are high).
>>>>>>>> 3. And then video data is transmitted to panel in LPM.
>>>>>>>> 4. At this time, operation mode of host controller becomes LPM.
>>>>>>>>
>>>>>>>> It seems that you says latter case.
>>>>>>>
>>>>>>> No. High speed clock and low power mode are orthogonal. Non-continuous
>>>>>>> mode simply means that the clock lane enters LP-11 between HS
>>>>>>> transmissions (see 5.6 "Clock Management" of the DSI specification).
>>>>>>>
>>>>>>
>>>>>> It seems that clock lane enters LP-11 regardless of HS clock enabled if
>>>>>> non-continous mode is used. Right?
>>>>>
>>>>> No, I think as long as HS clock is enabled the clock lane won't enter
>>>>> LP-11. Non-continuous mode means that the controller can disable the HS
>>>>> clock between HS transmissions. So in non-continuous mode the clock lane
>>>>> can enter LP-11 because the controller disables the HS clock.
>>>>
>>>> It makes me a little bit confusing. You said "if HS clock is enabled,
>>>> the the clock lane won't enter LP-11" But you said again "the clock lane
>>>> can enter LP-11 because the controller disables the HS clock" What is
>>>> the meaning?
>>>
>>> It means that if the HS clock is enabled, then the clock lane is not in
>>> LP-11. When the HS clock stops, then the clock lane enters LP-11.
>>>
>>>>> In continuous mode, then the clock will never be disabled, hence the
>>>>> clock lane will never enter LP-11.
>>>>>
>>>>>> And also it seems that non-continous mode is different from LPM at all
>>>>>> because with non-continuous mode, command data is transmitted to panel
>>>>>> in HS mode, but with LPM, command data is transmitted to panel in LP
>>>>>> mode. Also right?
>>>>>
>>>>> No. I think you can send command data to the peripheral in low power
>>>>> mode in both continuous and non-continuous clock modes.
>>>>>
>>>>>> If so, shouldn't the host driver disable HS clock, in case of LP mode,
>>>>>> before the host driver transmits command data?
>>>>>
>>>>> No. If the peripheral doesn't support non-continuous mode, then the HS
>>>>> clock must never be turned off. On the other hand, if the peripheral
>>>>> supports non-continuous mode, then the DSI host should automatically
>>>>> disable the HS clock between high-speed transmissions. That means if a
>>>>> packet is transmitted in low power mode the DSI host will not be
>>>>> transmitting in high-speed mode and therefore disable the HS clock.
>>>>
>>>> What is LPM you think? I thought LPM is LP-11 and HS clock disabled. So
>>>> for LPM transfer, lanes should be LP-11 state and also HS clock of the
>>>> host controller should be disabled.
>>>
>>> No. I don't think any transmissions can happen when all lanes are in
>>> LP-11 state. The MIPI_DSI_MSG_USE_LPM is used to specify that a packet
>>> should be transmitted in low power mode (see LP Transmission in 2.1
>>> "Definitions" of the MIPI DSI specification).
>>>
>>
>> Hm.. I see. I meant,
>>
>> if (flags & MIPI_DSI_MSG_USE_LPM)
>>        disable HS clock <- required.
>>
>> transmit command data <- in LPM.
> 
> No. Disabling the HS clock is not required for LPM mode. In fact if the
> peripheral specifies that it doesn't support non-continuous mode then
> the HS clock must *never* be disabled as long as the peripheral is in
> use.
> 
> MIPI_DSI_MSG_USE_LPM and MIPI_DSI_CLOCK_NON_CONTINUOUS are unrelated and
> need to be considered separately.

I mentioned already LPM and NON_CONTINUOUS are unrelated.

It seems that you say the only way to transfer command data in LPM is
non-continuous clock mode. However, you said and also the spec says,
"Non-continuous mode simply means that the clock lane enters LP-11
between HS transmissions". Doesn't *between HS transmissions" mean the
command data is transmitted in HS, *not in LPM*, and clock lane enters
LP-11 between them?

We have one lcd panel, nt35502a, which needs LPM transfer support
because it should receive some initial commands with LPM by default
hardware setting, and we faced with that the panel didn't work without
disabling HS clock before transmitting command data. How can you explain
that?

Thanks,
Inki Dae

> 
> Thierry
>