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 Fri, Aug 08, 2014 at 04:37:07PM +0900, Inki Dae wrote:
> On 2014년 08월 08일 16:03, Thierry Reding wrote:
> > On Fri, Aug 08, 2014 at 10:45:47AM +0900, Inki Dae wrote:
> >> On 2014년 08월 07일 22:55, Thierry Reding wrote:
> >>> On Thu, Aug 07, 2014 at 10:39:29PM +0900, Inki Dae wrote:
> >>>> On 2014년 08월 07일 22:17, Thierry Reding wrote:
> >>>>> On Thu, Aug 07, 2014 at 10:05:44PM +0900, Inki Dae wrote:
> >>>>>> On 2014년 08월 07일 20:09, Thierry Reding wrote:
> >>>>>>> On Thu, Aug 07, 2014 at 07:49:03PM +0900, Inki Dae wrote:
> >>>>>>>> On 2014년 08월 07일 18:09, Thierry Reding wrote:
> >>>>>>>>> On Thu, Aug 07, 2014 at 04:51:18PM +0900, Inki Dae wrote:
> >>>>>>>>>> On 2014년 08월 07일 15:58, Thierry Reding wrote:
> >>>>>>>>>>> On Thu, Aug 07, 2014 at 02:09:19AM +0900, Inki Dae wrote:
> >>>>>>>>>>>> 2014-08-06 16:43 GMT+09:00 Thierry Reding <thierry.reding@gmail.com>:
> >>>>>>>>> [...]
> >>>>>>>>>>>>> As far as I can tell non-continuous mode simply means that the host can
> >>>>>>>>>>>>> turn off the HS clock after a high-speed transmission. I think Andrzej
> >>>>>>>>>>>>> mentioned this already in another subthread, but this is an optional
> >>>>>>>>>>>>> mode that peripherals can support if they have extra circuitry that
> >>>>>>>>>>>>> provides an internal clock. Peripherals that don't have such circuitry
> >>>>>>>>>>>>> may rely on the HS clock to perform in between transmissions and
> >>>>>>>>>>>>> therefore require the HS clock to be always on (continuous mode). That's
> >>>>>>>>>>>>> what the MIPI_DSI_CLOCK_NON_CONTINUOUS flag is: it advertises that the
> >>>>>>>>>>>>> peripheral supports non-continuous mode and therefore the host can turn
> >>>>>>>>>>>>> the HS clock off after high-speed transmissions.
> >>>>>>>>>>>>
> >>>>>>>>>>>> What I don't make sure is this sentence. With
> >>>>>>>>>>>> MIPI_DSI_CLOCK_NON_CONTIUOUS flag, I guess two possible operations.
> >>>>>>>>>>>> One is,
> >>>>>>>>>>>> 1. host controller will generates signals if a bit of a register
> >>>>>>>>>>>> related to non-contiguous clock mode is set or unset.
> >>>>>>>>>>>> 2. And then video data is transmitted to panel in HS mode.
> >>>>>>>>>>>> 3. And then D-PHY detects LP-11 signal (positive and negative lane all
> >>>>>>>>>>>> are high).
> >>>>>>>>>>>> 4. And then D-PHY disables HS clock of host controller.
> >>>>>>>>>>>> 5. At this time, operation mode of host controller becomes LPM.
> >>>>>>>>>>>>
> >>>>>>>>>>>> Other is,
> >>>>>>>>>>>> 1. host controller will generates signals if a bit of a register
> >>>>>>>>>>>> related to non-contiguous clock mode is set or unset.
> >>>>>>>>>>>> 2. And then D-PHY detects LP-11 signal (positive and negative lane all
> >>>>>>>>>>>> are high).
> >>>>>>>>>>>> 3. And then video data is transmitted to panel in LPM.
> >>>>>>>>>>>> 4. At this time, operation mode of host controller becomes LPM.
> >>>>>>>>>>>>
> >>>>>>>>>>>> It seems that you says latter case.
> >>>>>>>>>>>
> >>>>>>>>>>> No. High speed clock and low power mode are orthogonal. Non-continuous
> >>>>>>>>>>> mode simply means that the clock lane enters LP-11 between HS
> >>>>>>>>>>> transmissions (see 5.6 "Clock Management" of the DSI specification).
> >>>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> It seems that clock lane enters LP-11 regardless of HS clock enabled if
> >>>>>>>>>> non-continous mode is used. Right?
> >>>>>>>>>
> >>>>>>>>> No, I think as long as HS clock is enabled the clock lane won't enter
> >>>>>>>>> LP-11. Non-continuous mode means that the controller can disable the HS
> >>>>>>>>> clock between HS transmissions. So in non-continuous mode the clock lane
> >>>>>>>>> can enter LP-11 because the controller disables the HS clock.
> >>>>>>>>
> >>>>>>>> It makes me a little bit confusing. You said "if HS clock is enabled,
> >>>>>>>> the the clock lane won't enter LP-11" But you said again "the clock lane
> >>>>>>>> can enter LP-11 because the controller disables the HS clock" What is
> >>>>>>>> the meaning?
> >>>>>>>
> >>>>>>> It means that if the HS clock is enabled, then the clock lane is not in
> >>>>>>> LP-11. When the HS clock stops, then the clock lane enters LP-11.
> >>>>>>>
> >>>>>>>>> In continuous mode, then the clock will never be disabled, hence the
> >>>>>>>>> clock lane will never enter LP-11.
> >>>>>>>>>
> >>>>>>>>>> And also it seems that non-continous mode is different from LPM at all
> >>>>>>>>>> because with non-continuous mode, command data is transmitted to panel
> >>>>>>>>>> in HS mode, but with LPM, command data is transmitted to panel in LP
> >>>>>>>>>> mode. Also right?
> >>>>>>>>>
> >>>>>>>>> No. I think you can send command data to the peripheral in low power
> >>>>>>>>> mode in both continuous and non-continuous clock modes.
> >>>>>>>>>
> >>>>>>>>>> If so, shouldn't the host driver disable HS clock, in case of LP mode,
> >>>>>>>>>> before the host driver transmits command data?
> >>>>>>>>>
> >>>>>>>>> No. If the peripheral doesn't support non-continuous mode, then the HS
> >>>>>>>>> clock must never be turned off. On the other hand, if the peripheral
> >>>>>>>>> supports non-continuous mode, then the DSI host should automatically
> >>>>>>>>> disable the HS clock between high-speed transmissions. That means if a
> >>>>>>>>> packet is transmitted in low power mode the DSI host will not be
> >>>>>>>>> transmitting in high-speed mode and therefore disable the HS clock.
> >>>>>>>>
> >>>>>>>> What is LPM you think? I thought LPM is LP-11 and HS clock disabled. So
> >>>>>>>> for LPM transfer, lanes should be LP-11 state and also HS clock of the
> >>>>>>>> host controller should be disabled.
> >>>>>>>
> >>>>>>> No. I don't think any transmissions can happen when all lanes are in
> >>>>>>> LP-11 state. The MIPI_DSI_MSG_USE_LPM is used to specify that a packet
> >>>>>>> should be transmitted in low power mode (see LP Transmission in 2.1
> >>>>>>> "Definitions" of the MIPI DSI specification).
> >>>>>>>
> >>>>>>
> >>>>>> Hm.. I see. I meant,
> >>>>>>
> >>>>>> if (flags & MIPI_DSI_MSG_USE_LPM)
> >>>>>>        disable HS clock <- required.
> >>>>>>
> >>>>>> transmit command data <- in LPM.
> >>>>>
> >>>>> No. Disabling the HS clock is not required for LPM mode. In fact if the
> >>>>> peripheral specifies that it doesn't support non-continuous mode then
> >>>>> the HS clock must *never* be disabled as long as the peripheral is in
> >>>>> use.
> >>>>>
> >>>>> MIPI_DSI_MSG_USE_LPM and MIPI_DSI_CLOCK_NON_CONTINUOUS are unrelated and
> >>>>> need to be considered separately.
> >>>>
> >>>> I mentioned already LPM and NON_CONTINUOUS are unrelated.
> >>>>
> >>>> It seems that you say the only way to transfer command data in LPM is
> >>>> non-continuous clock mode.
> >>>
> >>> No, that's not what I'm saying.
> >>>
> >>>> However, you said and also the spec says, "Non-continuous mode simply
> >>>> means that the clock lane enters LP-11 between HS transmissions".
> >>>> Doesn't *between HS transmissions" mean the command data is transmitted
> >>>> in HS, *not in LPM*, and clock lane enters LP-11 between them?
> >>>
> >>> Not necessarily. You can transmit command packets in high-speed mode,
> >>> but you don't have to. If you transmit packets in low power mode, then
> >>
> >> That would may why we are mentioning same comments repeatedly.
> >>
> >> In my case, host driver waits for the lane stop state (LP-11), and then
> >> disables HS clock to transmit command data in LPM. Of course, I'm not
> >> sure that yet it's correct way.
> > 
> > That's confusing. How can the lane go to LP-11 when the clock is still
> > running?
> 
> Actually, we are doing so. If the clock is still running then dsi driver
> will wait for stop state of the clock and data lanes. Know that this is
> valid only when initial time - just one time since power up.
> 
> 	/* Check clock and data lane state are stop state */
> 	timeout = 100;
> 	do {
> 		if (timeout-- == 0) {
> 			dev_err(dsi->dev, "waiting for bus lanes timed out\n");
> 			return -EFAULT;
> 		}
> 
> 		reg = readl(dsi->reg_base + DSIM_STATUS_REG);
> 		if ((reg & DSIM_STOP_STATE_DAT(lanes_mask))
> 		    != DSIM_STOP_STATE_DAT(lanes_mask))
> 			continue;
> 	} while (!(reg & (DSIM_STOP_STATE_CLK | DSIM_TX_READY_HS_CLK)));
> 
> > 
> >> In Tegra, What to do for it?
> > 
> > There are two bits in two separate registers for this:
> > 
> > 	DSI_HOST_CONTROL:
> > 	  bit 5: DSI_HIGH_SPEED_TRANS: DSI high speed transmission of
> > 	                               packets
> > 	    - 0 = LOW: low speed
> > 	    - 1 = HIGH: high speed
> > 
> > 	DSI_CONTROL:
> > 	  bit 20: DSI_HS_CLK_CTRL: Control for the HS clock lane
> > 	    - 0 = CONTINUOUS: HS clock is on all the time
> > 	    - 1 = TX_ONLY: HS clock is only active during HS
> > 	                   transmissions
> > 
> > So if the peripheral supports non-continuous mode of operation we set
> > the DSI_HS_CLK_CTRL bit, otherwise we clear it to make sure the clock
> > remains on all the time.
> >
> > When a packet is to be transmitted in high speed mode, we set the
> > DSI_HIGH_SPEED_TRANS bit. For low power mode transmissions that bit is
> > cleared.
> 
> That is exactly what I want. In your case, if you want to transmit
> command data in Low Power Mode in case of supporting non-continuous
> clock mode, then you would set DSI_HS_CLK_CTRL (TX_ONLY), and also you
> would clear DSI_HIGH_SPEED_TRANS (LOW).
> 
> So I guess,
> 
> if (flags & MIPI_DSI_MODE_NON_CONTINUOUS) {
>         disable DSI_HIGH_SPEED_TRANS;   <- LOW
>         enable DSI_HS_CLK_CTRL; <- TX_ONLY
> }
> 
> transmit command data <- in LPM.
> 
> However, what if the peripheral doesn't support non-continuous but want
> to transmit command data in LPM? Is that  impossible?

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;

Thierry

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