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

[Inki Dae <inki.dae@samsung.com>]

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@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.

Thanks,
Inki Dae

> For low power transmissions, only data lane 0 is used (with a clock
> embedded in the signal), therefore the clock lane (driven by the HS
> clock) can be in LP-11.
> 
> Thierry
>