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

[Andrzej Hajda]

On 07/29/2014 05:42 AM, Inki Dae wrote:
> On 2014년 07월 29일 00:50, Andrzej Hajda wrote:
>> On 07/28/2014 04:00 AM, Inki Dae wrote:
>>> This patch adds LPM transfer support for video or command data.
>>>
>>> With this patch, Exynos MIPI DSI controller can transfer command or
>>> video data with HS or LP mode in accordance with mode_flags set
>>> by LCD Panel driver.
>>>
>>> Changelog v2: Enable High Speed clock only in case of stand by request.
>>>
>>> Signed-off-by: Inki Dae <inki.dae at samsung.com>
>>> Acked-by: Kyungmin Park <kyungmin.park at samsung.com>
>>> ---
>>>  drivers/gpu/drm/exynos/exynos_drm_dsi.c |   22 ++++++++++++++++++++--
>>>  1 file changed, 20 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
>>> index 5e78d45..1bed105 100644
>>> --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
>>> +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
>>> @@ -493,8 +493,11 @@ static int exynos_dsi_enable_clock(struct exynos_dsi *dsi)
>>>  			| DSIM_ESC_PRESCALER(esc_div)
>>>  			| DSIM_LANE_ESC_CLK_EN_CLK
>>>  			| DSIM_LANE_ESC_CLK_EN_DATA(BIT(dsi->lanes) - 1)
>>> -			| DSIM_BYTE_CLK_SRC(0)
>>> -			| DSIM_TX_REQUEST_HSCLK;
>>> +			| DSIM_BYTE_CLK_SRC(0);
>>> +
>>> +	if (!(dsi->mode_flags & MIPI_DSI_MODE_CMD_LPM))
>>> +		reg |= DSIM_TX_REQUEST_HSCLK;
>>> +
>>>  	writel(reg, dsi->reg_base + DSIM_CLKCTRL_REG);
>>>  
>>>  	return 0;
>>> @@ -553,6 +556,18 @@ static void exynos_dsi_set_phy_ctrl(struct exynos_dsi *dsi)
>>>  	writel(reg, dsi->reg_base + DSIM_PHYTIMING2_REG);
>>>  }
>>>  
>>> +static void exynos_dsi_enable_hs_clock(struct exynos_dsi *dsi,
>>> +					bool enable)
>>> +{
>>> +	u32 reg = readl(dsi->reg_base + DSIM_CLKCTRL_REG);
>>> +
>>> +	reg &= ~DSIM_TX_REQUEST_HSCLK;
>>> +	if (enable)
>>> +		reg |= DSIM_TX_REQUEST_HSCLK;
>>> +
>>> +	writel(reg, dsi->reg_base + DSIM_CLKCTRL_REG);
>>> +}
>>> +
>> I have tested DSIM_TX_REQUEST_HSCLK bit on trats device(video mode HS) -
>> it works with and without the bit set.
> If you can test thmorstat board, you will face with that its panel is
> not worked.

So it means this panel requires proper driving of this bit, but it does
not prove it is
LPM related.

>> So I start to suspect this bit is not just for simply enable/disable HS
>> clock as function name suggests, do you know what is its
>> exact meaning? The specs are quite succinct on it.
> HSCLK only has meaning when it is used with CmdLpdt and TxLpdt bits.

This sounds very strange. DSI specs and D-PHY specs says clearly
that LPM transmissions are unrelated to HS clock [1][2]. Even timing
diagrams
in Exynos specs shows no dependency of LPM transmissions on HS clock.
And the
description of TxRequestHsClk bit says "HS clock request for HS transfer
at clock lane (Turn
on HS clock)".

Maybe different flag should be used to describe your panel requirements
regarding this bit.

It would be good to see the real initialization sequence in form of
pseudo-code or better in the driver.


[1]: MIPI DSI: "Note that in Low Power signaling mode, LP clock is
functionally embedded in the data signals. When LP
data transmission ends, the clock effectively stops and subsequent LP
clocks are not available to the
peripheral. The peripheral shall not require additional bits, bytes, or
packets from the host processor in
order to complete processing or pipeline movement of received data in LP
mode transmissions. There are a
variety of ways to meet this requirement. For example, the peripheral
may generate its own clock or it may
require the host processor to keep the HS serial clock running."

[2]: MIPI D-PHY: "The data is self-clocked by the applied bit encoding
and does not rely on the Clock Lane".

Regards
Andrzej

>
>> On the other side I have found DSIM_TX_LPDT_LP and DSIM_CMD_LPDT_LP bits
>> in DSIM_ESCMODE register
>> which seems to be related to flags you have introduced:
>> - DSIM_CMD_LPDT_LP - transmit commands in LP mode,
>> - DSIM_TX_LPDT_LP - transmit data in LP mode.
> As I mentioned already at other email thread, DSIM_TX_LPDT_LP specifies
> that host can transmit command and also image data to Panel in Low Power
> Mode. So these flags are specific to MIPI-DSI controller of Exynos.
>
>> The former is already triggered by MIPI_DSI_MSG_USE_LPM flag. Why do not
> This flag is set only when command msg transmission is requested by
> Panel driver. So we would need separated flags, MIPI_DSI_MODE_CMD_LPM
> and MIPI_DSI_MODE_VIDEO_LPM, to notify how host controller should
> transmit command and also image.
>
> Thanks,
> Inki Dae
>
>> you use the latter?
>>
>> Regards
>> Andrzej
>>
>>>  static void exynos_dsi_disable_clock(struct exynos_dsi *dsi)
>>>  {
>>>  	u32 reg;
>>> @@ -705,6 +720,9 @@ static void exynos_dsi_set_display_enable(struct exynos_dsi *dsi, bool enable)
>>>  {
>>>  	u32 reg;
>>>  
>>> +	if (!(dsi->mode_flags & MIPI_DSI_MODE_VIDEO_LPM) && enable)
>>> +		exynos_dsi_enable_hs_clock(dsi, true);
>>> +
>>>  	reg = readl(dsi->reg_base + DSIM_MDRESOL_REG);
>>>  	if (enable)
>>>  		reg |= DSIM_MAIN_STAND_BY;
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in
>> the body of a message to majordomo at vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>