[PATCH 1/2] drm/mipi-dsi: consider low power transmission

[Linus Walleij]

On Mon, Aug 18, 2014 at 10:11 AM Inki Dae <inki.dae at samsung.com> wrote:

> This patch adds a new flag, MIPI_DSI-MODE_LPM, to transmit data
> in low power. With this flag, msg.flags has MIPI_DSI_MSG_USE_LPM
> so that host driver of each SoC can clear or set relevant register
> bit for low power transmission.
>
> All host drivers shall support continuous clock behavior on the
> Clock Lane, and optionally may support non-continuous clock behavior.
> Both of them can transmit data in high speed of low power.
>
> With each clock behavior, non-continuous or continuous clock mode,
> host controller will transmit data in high speed by default so if
> peripheral wants to receive data in low power, the peripheral driver
> should set MIPI_DSI_MODE_LPM flag.
>
> Signed-off-by: Inki Dae <inki.dae at samsung.com>

Hi Inki Dae,

I recently used this flag in a driver to the effect that all writes become
LPM, including updates to a command mode-only panel, so the pixels
will draw very slowly on the screen. In this case I added the
feature for debugging (my display works fine in LP but not yet
in HS mode).

This is not a problem with a video mode panel since these are by
the specification required to operate in HS mode, so we know they
are always HS.

But in command mode, all commands are equal, even if they are
screen updates. I program my hardware to update the display
with a stream of commands, and with this flag set, that stream
will go slow.

Is this how it is intended?

Using the flag like this is kind of interesting because it is good for
debugging but I don't know if this is how it was intended.

If the flag is only supposed to be for DCS write commands, so that
both write and read happen in LP mode, then we
should probably rename it accordingly I think?

Yours,
Linus Walleij