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

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

On 2014년 08월 11일 16:50, Thierry Reding wrote:
> On Mon, Aug 11, 2014 at 04:35:46PM +0900, Inki Dae wrote:
>> On 2014년 08월 11일 16:24, Thierry Reding wrote:
>>> On Mon, Aug 11, 2014 at 02:19:21PM +0900, Inki Dae wrote:
>>>> On 2014년 08월 08일 18:55, Thierry Reding wrote:
> [...]
>>>>> The above is actually more like this:
>>>>>
>>>>> 	if ((flags & MIPI_DSI_MODE_NON_CONTINUOUS) == 0)
>>>>> 		clear DSI_HS_CLK_CTRL;
>>>>> 	else
>>>>> 		set DSI_HS_CLK_CTRL;
>>>>>
>>>>> 	if (msg->flags & MIPI_DSI_MSG_USE_LPM)
>>>>> 		clear DSI_HIGH_SPEED_TRANS;
>>>>> 	else
>>>>> 		set DSI_HIGH_SPEED_TRANS;
>>>>>
>>>>> So for peripherals that don't support non-continuous clock mode, this
>>>>> will result in the following for low-power transmissions:
>>>>>
>>>>> 	clear DSI_HS_CLK_CTRL; /* HS clock always on */
>>>>> 	clear DSI_HIGH_SPEED_TRANS;
>>>>
>>>> Right, then how host driver should check it if peripheral doesn't
>>>> support non-continuous clock mode? Or how the peripheral should notify
>>>> it to host driver? It would need a new flag instead of
>>>> MIPI_DSI_MODE_NON_CONTINUOUS.
>>>
>>> MIPI_DSI_MODE_NON_CONTINUOUS is exactly the flag that devices need to
>>> set to signal that they support non-continuous mode. If devices don't
>>> have that set, then the controller should always provide the HS clock.
>>>
>>> So, if MIPI_DSI_MODE_NON_CONTINUOUS is *not* set, then the peripheral
>>> does *not* support non-continuous mode.
>>>
>>
>> Again, assume that there is a peripheral that doesn't support
>> non-continuous clock mode but host driver want to transmit data in low
>> power. For this, you already mentioned like below,
>>
>> "So for peripherals that don't support non-continuous clock mode, this
>> will result in the following for low-power transmissions:
>>
>>  	clear DSI_HS_CLK_CTRL; /* HS clock always on */
>>  	clear DSI_HIGH_SPEED_TRANS;
>> "
>>
>> In this case, how should host driver check it to clear above two flags?
>> As you know, this is required to clear two flags same as non-continuous
>> clock mode. Don't you think that we need a new flag to identify them -
>> non-continuous clock mode or just for low-power transmission?
> 
> See what I wrote a little further up:
> 
>>>>> 	if ((flags & MIPI_DSI_MODE_NON_CONTINUOUS) == 0)
>>>>> 		clear DSI_HS_CLK_CTRL;
>>>>> 	else
>>>>> 		set DSI_HS_CLK_CTRL;
>>>>>
>>>>> 	if (msg->flags & MIPI_DSI_MSG_USE_LPM)
>>>>> 		clear DSI_HIGH_SPEED_TRANS;
>>>>> 	else
>>>>> 		set DSI_HIGH_SPEED_TRANS;
>>>>>
> 
> MIPI_DSI_MODE_NON_CONTINUOUS specifies that a peripheral supports non-
> continuous mode. When set, we clear DSI_HS_CLK_CTRL on Tegra because
> that tells the controller to turn off the HS clock between high-speed
> transmissions.
> 
> MIPI_DSI_MSG_USE_LPM specifies that a message is to be sent in low-power
> mode.
> 
> With the above two flags we can cover four cases:
> 
>   1) non-continuous mode with messages transmitted in low-power mode
>   2) non-continuous mode with messages transmitted in high-speed mode
>   3) continuous mode with messages transmitted in low-power mode

In case of 3), it would mean "set DSI_HS_CLK_CTRL" and "clear
DSI_HIGH_SPEED_TRANS". However, msg->flags has MIPI_DSI_MSG_USE_LPM but
dsi->mode_flags has no MIPI_DSI_MODE_NON_CONTINOUS flag..... Ah, right.
You mean that continuous mode is set by default implicitly?

Thanks,
Inki Dae

>   4) continuous mode with messages transmitted in high-speed mode
> 
> What other cases do you think we need to support?
> 
> Thierry
> 

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