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

[Inki Dae]

On 2014년 07월 29일 20:39, Andrzej Hajda wrote:
> 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)".

There are three System power states of D-PHY, Low-Power mode, High-Speed
mode and Ultra-Low Power mode. High-Speed mode needs 80Mbps ~ 1Gbps per
Lane. Therefore, to use HS mode, HS clock should be enabled. On the
other hand, LP mode needs only 10MHz (max).

So do you really think LP mode will be worked well with HS clock
enabled? The purpose of LP mode is to reduce power consumption while
transmitting data. Can you reduce the power consumption in LP mode with
HS clock enabled?

Thanks,
Inki Dae

> 
> 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
>>>
>>
> 
> --
> 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
>