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

[Thierry Reding <thierry.reding@gmail.com>]

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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
  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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