Re: [PATCH 3/5] drm/msm/dsi_pll_10nm: Fix bad VCO rate calculation and prescaler

From: Rob Clark
Date: Tue Feb 02 2021 - 14:11:42 EST

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In reply to: AngeloGioacchino Del Regno: "Re: [PATCH 3/5] drm/msm/dsi_pll_10nm: Fix bad VCO rate calculation and prescaler"
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On Tue, Feb 2, 2021 at 10:46 AM AngeloGioacchino Del Regno
<angelogioacchino.delregno@xxxxxxxxxxxxxx> wrote:
>
> Il 02/02/21 19:45, Rob Clark ha scritto:
> > On Tue, Feb 2, 2021 at 6:32 AM AngeloGioacchino Del Regno
> > <angelogioacchino.delregno@xxxxxxxxxxxxxx> wrote:
> >>
> >> Il 01/02/21 18:31, Rob Clark ha scritto:
> >>> On Mon, Feb 1, 2021 at 9:18 AM Rob Clark <robdclark@xxxxxxxxx> wrote:
> >>>>
> >>>> On Mon, Feb 1, 2021 at 9:05 AM Rob Clark <robdclark@xxxxxxxxx> wrote:
> >>>>>
> >>>>> On Mon, Feb 1, 2021 at 7:47 AM Rob Clark <robdclark@xxxxxxxxx> wrote:
> >>>>>>
> >>>>>> On Mon, Feb 1, 2021 at 2:11 AM AngeloGioacchino Del Regno
> >>>>>> <angelogioacchino.delregno@xxxxxxxxxxxxxx> wrote:
> >>>>>>>
> >>>>>>> Il 31/01/21 20:50, Rob Clark ha scritto:
> >>>>>>>> On Sat, Jan 9, 2021 at 5:51 AM AngeloGioacchino Del Regno
> >>>>>>>> <angelogioacchino.delregno@xxxxxxxxxxxxxx> wrote:
> >>>>>>>>>
> >>>>>>>>> The VCO rate was being miscalculated due to a big overlook during
> >>>>>>>>> the process of porting this driver from downstream to upstream:
> >>>>>>>>> here we are really recalculating the rate of the VCO by reading
> >>>>>>>>> the appropriate registers and returning a real frequency, while
> >>>>>>>>> downstream the driver was doing something entirely different.
> >>>>>>>>>
> >>>>>>>>> In our case here, the recalculated rate was wrong, as it was then
> >>>>>>>>> given back to the set_rate function, which was erroneously doing
> >>>>>>>>> a division on the fractional value, based on the prescaler being
> >>>>>>>>> either enabled or disabled: this was actually producing a bug for
> >>>>>>>>> which the final VCO rate was being doubled, causing very obvious
> >>>>>>>>> issues when trying to drive a DSI panel because the actual divider
> >>>>>>>>> value was multiplied by two!
> >>>>>>>>>
> >>>>>>>>> To make things work properly, remove the multiplication of the
> >>>>>>>>> reference clock by two from function dsi_pll_calc_dec_frac and
> >>>>>>>>> account for the prescaler enablement in the vco_recalc_rate (if
> >>>>>>>>> the prescaler is enabled, then the hardware will divide the rate
> >>>>>>>>> by two).
> >>>>>>>>>
> >>>>>>>>> This will make the vco_recalc_rate function to pass the right
> >>>>>>>>> frequency to the (clock framework) set_rate function when called,
> >>>>>>>>> which will - in turn - program the right values in both the
> >>>>>>>>> DECIMAL_DIV_START_1 and the FRAC_DIV_START_{LOW/MID/HIGH}_1
> >>>>>>>>> registers, finally making the PLL to output the right clock.
> >>>>>>>>>
> >>>>>>>>> Also, while at it, remove the prescaler TODO by also adding the
> >>>>>>>>> possibility of disabling the prescaler on the PLL (it is in the
> >>>>>>>>> PLL_ANALOG_CONTROLS_ONE register).
> >>>>>>>>> Of course, both prescaler-ON and OFF cases were tested.
> >>>>>>>>
> >>>>>>>> This somehow breaks things on sc7180 (display gets stuck at first
> >>>>>>>> frame of splash screen). (This is a setup w/ an ti-sn65dsi86 dsi->eDP
> >>>>>>>> bridge)
> >>>>>>>>
> >>>>>>>
> >>>>>>> First frame of the splash means that something is "a bit" wrong...
> >>>>>>> ...like the DSI clock is a little off.
> >>>>>>>
> >>>>>>> I don't have such hardware, otherwise I would've tried... but what you
> >>>>>>> describe is a bit strange.
> >>>>>>> Is there any other older qcom platform using this chip? Any other
> >>>>>>> non-qcom platform? Is the driver for the SN65DSI86 surely fine?
> >>>>>>> Anyway, as you know, I would never propose untested patches nor
> >>>>>>> partially working ones for any reason: I'm sorry that this happened.
> >>>>>>
> >>>>>> I don't think there is anything publicly avail w/ sc7180 (yet.. but very soon)
> >>>>>>
> >>>>>> The ti-sn65dsi86 bridge is used on a bunch of 845/850 devices (like
> >>>>>> the snapdragon windows laptops).. and I think also the older 835
> >>>>>> laptops.. ofc that doesn't mean that there isn't some bug, but I'd
> >>>>>> guess maybe more likely that there is some small difference in DSI vs
> >>>>>> older devices, or some cmd vs video mode difference.
> >>>>>>
> >>>>>> Anyways, seems like the screen did eventually recover so that gives me
> >>>>>> a bit of confidence to bisect this series, which I'll do a bit later
> >>>>>> today.
> >>>>>
> >>>>> fwiw, this series minus this patch, and everything looks ok.. let me
> >>>>> take a closer look at what changes with this patch
> >>>>
> >>>> Btw, it looks like upstream, config->disable_prescaler is always
> >>>> false.. I don't suppose you have anything WIP that changes this?
> >>>
> >>
> >> Regarding that one, I have tested the driver in both cases, with
> >> and without prescaler enabled (both worked fine), then I have decided
> >> to leave the prescaler option exactly as the previous default.
> >>
> >> My plan about this was/still is:
> >> 1. Wait until this one gets merged (gives me time to also look
> >> at the other billion patches that I've sent);
> >> 2. Add the prescaler option DT property and explain that it has
> >> to be used only with "puny" displays (low resolution, low
> >> clocks) as with "good ones", enabling the prescaler gives less
> >> clock jitter (and some microamps more power consumption);
> >> 3. Add the Spread Spectrum Clock (SSC) functionality with related
> >> DT properties.
> >>
> >> Point 2 and 3 would go in the same series, unless someone does
> >> N.2 before I do... and N.3 requires a bit of extensive testing,
> >> which I have already partially started on the FxTec phone.
> >>
> >>> fwiw, this is the clk_summary diff with and without this patch:
> >>>
> >>> ------------------
> >>> 270,282c270,282
> >>> < dsi0_pll_out_div_clk 1 1 0
> >>> 887039941 0 0 50000 Y
> >>> < dsi0_pll_post_out_div_clk 0 0 0
> >>> 221759985 0 0 50000 Y
> >>> < dsi0_pll_bit_clk 2 2 0
> >>> 887039941 0 0 50000 Y
> >>> < dsi0_pclk_mux 1 1 0
> >>> 887039941 0 0 50000 Y
> >>> < dsi0_phy_pll_out_dsiclk 1 1 0
> >>> 147839991 0 0 50000 Y
> >>> < disp_cc_mdss_pclk0_clk_src 1 1 0
> >>> 147839991 0 0 50000 Y
> >>> < disp_cc_mdss_pclk0_clk 1 1 0
> >>> 147839991 0 0 50000 Y
> >>> < dsi0_pll_by_2_bit_clk 0 0 0
> >>> 443519970 0 0 50000 Y
> >>> < dsi0_phy_pll_out_byteclk 1 1 0
> >>> 110879992 0 0 50000 Y
> >>> < disp_cc_mdss_byte0_clk_src 2 2 0
> >>> 110879992 0 0 50000 Y
> >>> < disp_cc_mdss_byte0_div_clk_src 1 1
> >>> 0 55439996 0 0 50000 Y
> >>> < disp_cc_mdss_byte0_intf_clk 1 1
> >>> 0 55439996 0 0 50000 Y
> >>> < disp_cc_mdss_byte0_clk 1 1 0
> >>> 110879992 0 0 50000 Y
> >>> ---
> >>>> dsi0_pll_out_div_clk 1 1 0 887039978 0 0 50000 Y
> >>>> dsi0_pll_post_out_div_clk 0 0 0 221759994 0 0 50000 Y
> >>>> dsi0_pll_bit_clk 2 2 0 887039978 0 0 50000 Y
> >>>> dsi0_pclk_mux 1 1 0 887039978 0 0 50000 Y
> >>>> dsi0_phy_pll_out_dsiclk 1 1 0 147839997 0 0 50000 Y
> >>>> disp_cc_mdss_pclk0_clk_src 1 1 0 147839997 0 0 50000 Y
> >>>> disp_cc_mdss_pclk0_clk 1 1 0 147839997 0 0 50000 Y
> >>>> dsi0_pll_by_2_bit_clk 0 0 0 443519989 0 0 50000 Y
> >>>> dsi0_phy_pll_out_byteclk 1 1 0 110879997 0 0 50000 Y
> >>>> disp_cc_mdss_byte0_clk_src 2 2 0 110879997 0 0 50000 Y
> >>>> disp_cc_mdss_byte0_div_clk_src 1 1 0 55439999 0 0 50000 Y
> >>>> disp_cc_mdss_byte0_intf_clk 1 1 0 55439999 0 0 50000 Y
> >>>> disp_cc_mdss_byte0_clk 1 1 0 110879997 0 0 50000 Y
> >>> ------------------
> >>>
> >>>
> >>
> >> This is almost exactly what I saw on my devices as well, you get a
> >> difference of "just some Hz" (which can be totally ignored), because
> >> of how the calculation is done now.
> >>
> >> Thing is, what you see as PIXEL and BYTE clocks *before* the change is
> >> Linux thinking that your DSI is at that frequency, while the PLL will
> >> output *half* the rate, which is exactly what the patch fixes.
> >>
> >> "Fun" story is: the Xperia XZ1 (8998) and XZ (8996) have got the same
> >> display... by lowering the DSI rate on the MSM8996 phone by half, I
> >> get the same *identical* issues as the 8998 one without this patch.
> >> The clocks all match between one and another, because.. it's.. the same
> >> display, after all.
> >>
> >> It is because of the aforementioned test that I have raised doubts about
> >> the TI chip driver (or anything else really).. but then, anything is
> >> possible.
> >
> > It does look like, *so far* the TI bridge chip is only used on qc
> > platforms (according to grep'ing dts), so I suppose I can't rule out
> > bugs which cancel each other out. Although there are various other
> > bridges used (for ex, the sdm845 rb3 board has some dsi->hdmi bridge)
> >
>
> Argh...
>
> > I guess it would be useful if we could measure the clk somehow to
> > confirm that it is running at the rate we think it is..
> >
>
> I totally agree with you on this, I actually wanted to do it the proper
> way, but then these clocks are really too high for my cheap oscilloscope
> and I couldn't... :(

Ok, there might actually be a way to do this.. there is a testclock
utility (added sboyd who wrote it in CC):

https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/refs/heads/main/chipset-qc845/dev-util/testclock/files/testclock.py

there is a similar thing for sc7180.. for other devices, I guess it
would require some porting..

Looking at disp_cc_mdss_byte0_clk and disp_cc_mdss_pclk0_clk on
sc7180, the rates returned by testclock roughly match what is in
clk_summary, ie. within rounding error

BR,
-R

> >
> >
> >>>>>
> >>>>>>> In any case, just to be perfectly transparent, while being here waiting
> >>>>>>> for review, this patch series got tested on more smartphones, even ones
> >>>>>>> that I don't personally own, with different displays.
> >>>>>>>
> >>>>>>> For your reference, here's a list (all MSM8998..):
> >>>>>>> - OnePlus 5 (1920x1080)
> >>>>>>> - F(x)Tec Pro 1 (2160x1080)
> >>>>>>> - Sony Xperia XZ1 Compact (1280x720)
> >>>>>>> - Sony Xperia XZ1 (1920x1080)
> >>>>>>> - Sony Xperia XZ Premium (3840x2160)
> >>>>>>>
> >>>>>>
> >>>>>> Yeah, no worries, I wasn't trying to imply that the patch was untested.
> >>>>>>
> >>
> >> I know, of course!
> >>
> >>>>>> Out of curiosity, are any of those video mode panels?
> >>
> >> Yes and "also":
> >> The FxTec Pro1 has a video mode panel, for which I'm trying to upstream
> >> the driver...look here: https://lore.kernel.org/patchwork/patch/1365228/
> >>
> >> The Xperia XZ Premium has a Sharp LS055D1SX04 panel under NT35950, which
> >> can be configured as command or as video mode... I tried both modes, but
> >> there is some issue with the DPU1/DSI drivers and *DUAL DSI*, as cmd
> >> does work with some tearing, but video doesn't even start (downstream it
> >> works).
> >>
> >> So the only video mode panel that I could test is that BOE panel on the
> >> FxTec phone (single dsi), which works just great.
> >>
> >>>>>>
> >>>>>>>
> >>>>>>>> Also, something (I assume DSI related) that I was testing on
> >>>>>>>> msm-next-staging seems to have effected the colors on the panel (ie.
> >>>>>>>> they are more muted).. which seems to persist across reboots (ie. when
> >>>>>>>
> >>>>>>> So much "fun". This makes me think something about the PCC block doing
> >>>>>>> the wrong thing (getting misconfigured).
> >>>>>>>
> >>>>>>>> switching back to a good kernel), and interestingly if I reboot from a
> >>>>>>>> good kernel I see part of the login prompt (or whatever was previously
> >>>>>>>> on-screen) in the firmware ui screen !?! (so maybe somehow triggered
> >>>>>>>> the display to think it is in PSR mode??)
> >>>>>>>>
> >>>>>>>
> >>>>>>> From a fast read, the SN65DSI86 is on I2C.. giving it a wrong dsi clock
> >>>>>>> cannot produce (logically, at least) this, so I say that it is very
> >>>>>>> unlikely for this to be a consequence of the 10nm pll fixes...
> >>>>>>>
> >>>>>>
> >>>>>> Note that the bridge can also be programmed via dsi cmd mode packets,
> >>>>>> which I believe is the case on the 835 laptops (or at least one of
> >>>>>> them).. but all the things I have are using i2c as the control path.
> >>>>>>
> >>>>>>> ...unless the bootloader is not configuring the DSI rates, but that's
> >>>>>>> also veeeeery unlikely (it always does, or it always does not).
> >>>>>>
> >>>>>> I haven't looked at the bootloader display code, but booting back to
> >>>>>> an old/good kernel didn't change anything.. even powering off didn't.
> >>>>>> But the ghost image seemed to fade after some time, and by the next
> >>>>>> morning it was fine. Which is strange. (But tbf, I'm more a gpu guy
> >>>>>> who works on display only when necessary.. ie. a gpu without a display
> >>>>>> isn't so much fun ;-))
> >>>>>>
> >>
> >> OpenCL all the way! lol :D
> >>
> >> On Qualcomm platforms, the first thing that I've ever done was to bring
> >> up displays on 8974 Sony platforms... (we're talking about years ago).
> >>
> >> I'm a lil more on the display side of things (but growing a beard while
> >> waiting between a frame and another due to no GPU isn't so much fun
> >> either!).
> >>
> >>>>>>>> Not sure if that is caused by these patches, but if I can figure out
> >>>>>>>> how to get the panel back to normal I can bisect. I think for now
> >>>>>>>> I'll drop this series. Possibly it could be a
> >>>>>>>> two-wrongs-makes-a-right situation that had things working before, but
> >>>>>>>> I think someone from qcom who knows the DSI IP should take a look.
> >>>>>>>>
> >>>>>>>
> >>>>>>> I would be happy if someone from Qualcomm takes a look: after all, there
> >>>>>>> is no documentation and they're the only ones that can verify this kind
> >>>>>>> of stuff. Please, Qualcomm.
> >>>>>>
> >>>>>> Hopefully someone can take a look.
> >>>>>>
> >>>>>>> Besides that, if there's anything I can help with to solve this riddle,
> >>>>>>> I'm here for you.
> >>>>>>
> >>>>>> Thanks, like I said I'll try applying the patches one by one and see
> >>>>>> if I can narrow down what made the panel go funny, and we can go from
> >>>>>> there
> >>>>>>
> >>>>>> BR,
> >>>>>> -R
> >>>>>>
> >>>>>>> Yours,
> >>>>>>> -- Angelo
> >>>>>>>
> >>>>>>>> BR,
> >>>>>>>> -R
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxxx>
> >>>>>>>>> ---
> >>>>>>>>> drivers/gpu/drm/msm/dsi/pll/dsi_pll_10nm.c | 22 +++++++++-------------
> >>>>>>>>> 1 file changed, 9 insertions(+), 13 deletions(-)
> >>>>>>>>>
> >>>>>>>>> diff --git a/drivers/gpu/drm/msm/dsi/pll/dsi_pll_10nm.c b/drivers/gpu/drm/msm/dsi/pll/dsi_pll_10nm.c
> >>>>>>>>> index 8b66e852eb36..5be562dfbf06 100644
> >>>>>>>>> --- a/drivers/gpu/drm/msm/dsi/pll/dsi_pll_10nm.c
> >>>>>>>>> +++ b/drivers/gpu/drm/msm/dsi/pll/dsi_pll_10nm.c
> >>>>>>>>> @@ -165,11 +165,7 @@ static void dsi_pll_calc_dec_frac(struct dsi_pll_10nm *pll)
> >>>>>>>>>
> >>>>>>>>> pll_freq = pll->vco_current_rate;
> >>>>>>>>>
> >>>>>>>>> - if (config->disable_prescaler)
> >>>>>>>>> - divider = fref;
> >>>>>>>>> - else
> >>>>>>>>> - divider = fref * 2;
> >>>>>>>>> -
> >>>>>>>>> + divider = fref;
> >>>>>>>>> multiplier = 1 << config->frac_bits;
> >>>>>>>>> dec_multiple = div_u64(pll_freq * multiplier, divider);
> >>>>>>>>> dec = div_u64_rem(dec_multiple, multiplier, &frac);
> >>>>>>>>> @@ -266,9 +262,11 @@ static void dsi_pll_ssc_commit(struct dsi_pll_10nm *pll)
> >>>>>>>>>
> >>>>>>>>> static void dsi_pll_config_hzindep_reg(struct dsi_pll_10nm *pll)
> >>>>>>>>> {
> >>>>>>>>> + struct dsi_pll_config *config = &pll->pll_configuration;
> >>>>>>>>> void __iomem *base = pll->mmio;
> >>>>>>>>> + u32 val = config->disable_prescaler ? 0x0 : 0x80;
> >>>>>>>>>
> >>>>>>>>> - pll_write(base + REG_DSI_10nm_PHY_PLL_ANALOG_CONTROLS_ONE, 0x80);
> >>>>>>>>> + pll_write(base + REG_DSI_10nm_PHY_PLL_ANALOG_CONTROLS_ONE, val);
> >>>>>>>>> pll_write(base + REG_DSI_10nm_PHY_PLL_ANALOG_CONTROLS_TWO, 0x03);
> >>>>>>>>> pll_write(base + REG_DSI_10nm_PHY_PLL_ANALOG_CONTROLS_THREE, 0x00);
> >>>>>>>>> pll_write(base + REG_DSI_10nm_PHY_PLL_DSM_DIVIDER, 0x00);
> >>>>>>>>> @@ -499,17 +497,15 @@ static unsigned long dsi_pll_10nm_vco_recalc_rate(struct clk_hw *hw,
> >>>>>>>>> frac |= ((pll_read(base + REG_DSI_10nm_PHY_PLL_FRAC_DIV_START_HIGH_1) &
> >>>>>>>>> 0x3) << 16);
> >>>>>>>>>
> >>>>>>>>> - /*
> >>>>>>>>> - * TODO:
> >>>>>>>>> - * 1. Assumes prescaler is disabled
> >>>>>>>>> - */
> >>>>>>>>> multiplier = 1 << config->frac_bits;
> >>>>>>>>> - pll_freq = dec * (ref_clk * 2);
> >>>>>>>>> - tmp64 = (ref_clk * 2 * frac);
> >>>>>>>>> + pll_freq = dec * ref_clk;
> >>>>>>>>> + tmp64 = ref_clk * frac;
> >>>>>>>>> pll_freq += div_u64(tmp64, multiplier);
> >>>>>>>>> -
> >>>>>>>>> vco_rate = pll_freq;
> >>>>>>>>>
> >>>>>>>>> + if (config->disable_prescaler)
> >>>>>>>>> + vco_rate = div_u64(vco_rate, 2);
> >>>>>>>>> +
> >>>>>>>>> DBG("DSI PLL%d returning vco rate = %lu, dec = %x, frac = %x",
> >>>>>>>>> pll_10nm->id, (unsigned long)vco_rate, dec, frac);
> >>>>>>>>>
> >>>>>>>>> --
> >>>>>>>>> 2.29.2
> >>>>>>>>>
> >>>>>>>
> >>
>

Next message: Dan Carpenter: "Re: [PATCH 4.4 24/28] can: dev: prevent potential information leak in can_fill_info()"
Previous message: Andrea Mayer: "[PATCH net-next] seg6: fool-proof the processing of SRv6 behavior attributes"
In reply to: AngeloGioacchino Del Regno: "Re: [PATCH 3/5] drm/msm/dsi_pll_10nm: Fix bad VCO rate calculation and prescaler"
Next in thread: Rob Clark: "Re: [PATCH 3/5] drm/msm/dsi_pll_10nm: Fix bad VCO rate calculation and prescaler"
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