Re: [PATCH v6 11/22] clk: sunxi-ng: a64: Add minimum rate for PLL_MIPI

From: Michael Nazzareno Trimarchi
Date: Fri Jul 05 2019 - 13:52:45 EST

Hi Maxime

On Wed, Jul 3, 2019 at 1:49 PM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
>
> On Tue, Jun 25, 2019 at 09:00:36PM +0530, Jagan Teki wrote:
> > On Tue, Jun 25, 2019 at 8:19 PM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
> > >
> > > On Thu, Jun 20, 2019 at 11:57:44PM +0530, Jagan Teki wrote:
> > > > On Fri, Jun 14, 2019 at 7:54 PM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
> > > > >
> > > > > On Wed, Jun 05, 2019 at 01:03:16PM +0530, Jagan Teki wrote:
> > > > > > On Wed, Jun 5, 2019 at 12:19 PM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
> > > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > I've reordered the mail a bit to work on chunks
> > > > > > >
> > > > > > > On Fri, May 24, 2019 at 03:37:42PM +0530, Jagan Teki wrote:
> > > > > > > > > I wish it was in your commit log in the first place, instead of having
> > > > > > > > > to exchange multiple mails over this.
> > > > > > > > >
> > > > > > > > > However, I don't think that's quite true, and it might be a bug in
> > > > > > > > > Allwinner's implementation (or rather something quite confusing).
> > > > > > > > >
> > > > > > > > > You're right that the lcd_rate and pll_rate seem to be generated from
> > > > > > > > > the pixel clock, and it indeed looks like the ratio between the pixel
> > > > > > > > > clock and the TCON dotclock is defined through the number of bits per
> > > > > > > > > lanes.
> > > > > > > > >
> > > > > > > > > However, in this case, dsi_rate is actually the same than lcd_rate,
> > > > > > > > > since pll_rate is going to be divided by dsi_div:
> > > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L791
> > > > > > > > >
> > > > > > > > > Since lcd_div is 1, it also means that in this case, dsi_rate ==
> > > > > > > > > dclk_rate.
> > > > > > > > >
> > > > > > > > > The DSI module clock however, is always set to 148.5 MHz. Indeed, if
> > > > > > > > > we look at:
> > > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L804
> > > > > > > > >
> > > > > > > > > We can see that the rate in clk_info is used if it's different than
> > > > > > > > > 0. This is filled by disp_al_lcd_get_clk_info, which, in the case of a
> > > > > > > > > DSI panel, will hardcode it to 148.5 MHz:
> > > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/disp_al.c#L164
> > > > > > > >
> > > > > > > > Let me explain, something more.
> > > > > > > >
> > > > > > > > According to bsp there are clk_info.tcon_div which I will explain below.
> > > > > > > > clk_info.dsi_div which is dynamic and it depends on bpp/lanes, so it
> > > > > > > > is 6 for 24bpp and 4 lanes devices.
> > > > > > > >
> > > > > > > > PLL rate here depends on dsi_div (not tcon_div)
> > > > > > > >
> > > > > > > > Code here
> > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L784
> > > > > > > >
> > > > > > > > is computing the actual set rate, which depends on dsi_rate.
> > > > > > > >
> > > > > > > > lcd_rate = dclk_rate * clk_info.dsi_div;
> > > > > > > > dsi_rate = pll_rate / clk_info.dsi_div;
> > > > > > > >
> > > > > > > > Say if the dclk_rate 148MHz then the dsi_rate is 888MHz which set rate
> > > > > > > > for above link you mentioned.
> > > > > > > >
> > > > > > > > Here are the evidence with some prints.
> > > > > > > >
> > > > > > > > https://gist.github.com/openedev/9bae2d87d2fcc06b999fe48c998b7043
> > > > > > > > https://gist.github.com/openedev/700de2e3701b2bf3ad1aa0f0fa862c9a
> > > > > > >
> > > > > > > Ok, so we agree up to this point, and the prints confirm that the
> > > > > > > analysis above is the right one.
> > > > > > >
> > > > > > > > > So, the DSI clock is set to this here:
> > > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L805
> > > > > > >
> > > > > > > Your patch doesn't address that, so let's leave that one alone.
> > > > > >
> > > > > > Basically this is final pll set rate when sun4i_dotclock.c called the
> > > > > > desired rate with ccu_nkm.c so it ended the final rate with parent as
> > > > > > Line 8 of
> > > > > > https://gist.github.com/openedev/700de2e3701b2bf3ad1aa0f0fa862c9a
> > > > >
> > > > > If that's important to the driver, it should be set explicitly then,
> > > > > and not work by accident.
> > > > >
> > > > > > > > > The TCON *module* clock (the one in the clock controller) has been set
> > > > > > > > > to lcd_rate (so the pixel clock times the number of bits per lane) here:
> > > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L800
> > > > > > > > >
> > > > > > > > > And the PLL has been set to the same rate here:
> > > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L794
> > > > > > > > >
> > > > > > > > > Let's take a step back now: that function we were looking at,
> > > > > > > > > lcd_clk_config, is called by lcd_clk_enable, which is in turn called
> > > > > > > > > by disp_lcd_enable here:
> > > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L1328
> > > > > > > > >
> > > > > > > > > The next function being called is disp_al_lcd_cfg, and that function
> > > > > > > > > will hardcode the TCON dotclock divider to 4, here:
> > > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/disp_al.c#L240
> > > > > > > >
> > > > > > > > tcon_div from BSP point-of-view of there are two variants
> > > > > > > > 00) clk_info.tcon_div which is 4 and same is set the divider position
> > > > > > > > in SUN4I_TCON0_DCLK_REG (like above link refer)
> > > > > > > > 01) tcon_div which is 4 and used for edge timings computation
> > > > > > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c#L12
> > > > > > > >
> > > > > > > > The real reason for 01) is again 4 is they set the divider to 4 in 00)
> > > > > > > > which is technically wrong because the dividers which used during
> > > > > > > > dotclock in above (dsi_div) should be used here as well. Since there
> > > > > > > > is no dynamic way of doing this BSP hard-coding these values.
> > > > > > > >
> > > > > > > > Patches 5,6,7 on this series doing this
> > > > > > > > https://patchwork.freedesktop.org/series/60847/
> > > > > > > >
> > > > > > > > Hope this explanation helps?
> > > > > > >
> > > > > > > It doesn't.
> > > > > > >
> > > > > > > The clock tree is this one:
> > > > > > >
> > > > > > > PLL(s) -> TCON module clock -> TCON dotclock.
> > > > > > >
> > > > > > > The links I mentioned above show that the clock set to lcd_rate is the
> > > > > > > TCON module clocks (and it should be the one taking the bpp and lanes
> > > > > > > into account), while the TCON dotclock uses a fixed divider of 4.
> > > > > >
> > > > > > Sorry, I can argue much other-than giving some code snips, according to [1]
> > > > > >
> > > > > > 00) Line 785, 786 with dclk_rate 148000000
> > > > > >
> > > > > > lcd_rate = dclk_rate * clk_info.dsi_div;
> > > > > > pll_rate = lcd_rate * clk_info.lcd_div;
> > > > > >
> > > > > > Since dsi_div is 6 (bpp/lanes), lcd_div 1
> > > > > >
> > > > > > lcd_rate = 888000000, pll_rate = 888000000
> > > > > >
> > > > > > 01) Line 801, 804 are final rates computed as per clock driver (say
> > > > > > ccu_nkm in mainline)
> > > > > >
> > > > > > lcd_rate_set=891000000
> > > > > >
> > > > > > As per your comments if it would be 4 then the desired numbers are
> > > > > > would be 592000000 not 888000000.
> > > > > >
> > > > > > This is what I'm trying to say in all mails, and same as verified with
> > > > > > 2-lanes devices as well where the dsi_div is 12 so the final rate is
> > > > > > 290MHz * 12
> > > > >
> > > > > In the code you sent, you're forcing a divider on the internal TCON
> > > > > clock, while that one is fixed in the BSP.
> > > > >
> > > > > There's indeed the bpp / lanes divider, but it's used in the *parent*
> > > > > clock of the one you're changing.
> > > > >
> > > > > And the dsi0_clk clock you pointed out in the code snippet is yet
> > > > > another clock, the MIPI DSI module clock.
> > > >
> > > > Correct, look like I refereed wrong reference in the above mail. sorry
> > > > for the noise.
> > > >
> > > > Actually I'm trying to explain about pll_rate here which indeed
> > > > depends on dsi.div
> > > > https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L786
> > > >
> > > > lcd_rate = dclk_rate * clk_info.dsi_div;
> > > > pll_rate = lcd_rate * clk_info.lcd_div;
> > > >
> > > > Say
> > > >
> > > > 1) For 148MHz dclk_rate with dsi_div is 6 (24/4) lcd_div is 1 which
> > > > resulting pll_rate is 888MHz.
> > > >
> > > > 2) For 30MHz dclk_rate with 4 lane and 24 RGB the resulting pll_rate is 180MHz
> > > >
> > > > 3) For 27.5MHz dclk_rate with 2 lane and 24 RGB the resulting pll_rate is 330MHz
> > > >
> > > > Here is the few more logs in code, for case 2)
> > > >
> > > > [ 1.920441] sun4i_dclk_round_rate: min_div = 6 max_div = 6, rate = 30000000
> > > > [ 1.920505] ideal = 180000000, rounded = 178200000
> > > > [ 1.920509] sun4i_dclk_round_rate: div = 6 rate = 29700000
> > > > [ 1.920514] sun4i_dclk_round_rate: min_div = 6 max_div = 6, rate = 30000000
> > > > [ 1.920532] ideal = 1800ls and one DSI-RGB bridge. All of them do use
> > PLL_MIPI (pll_rate) and it indeed depends on bpp/lanes
> >00000, rounded = 178200000
> > > > [ 1.920535] sun4i_dclk_round_rate: div = 6 rate = 29700000
> > > > [ 1.920572] sun4i_dclk_recalc_rate: val = 1, rate = 178200000
> > > > [ 1.920576] sun4i_dclk_recalc_rate: val = 1, rate = 178200000
> > > > [ 1.920597] rate = 178200000
> > > > [ 1.920599] parent_rate = 297000000
> > > > [ 1.920602] reg = 0x90c00000
> > > > [ 1.920605] _nkm.n = 3, nkm->n.offset = 0x1, nkm->n.shift = 8
> > > > [ 1.920609] _nkm.k = 2, nkm->k.offset = 0x1, nkm->k.shift = 4
> > > > [ 1.920612] _nkm.m = 10, nkm->m.offset = 0x1, nkm->m.shift = 0
> > > > [ 1.920958] sun4i_dclk_set_rate div 6
> > > > [ 1.920966] sun4i_dclk_recalc_rate: val = 6, rate = 29700000
> > > >
> > > > and clk_summary:
> > > >
> > > > pll-video0 1 1 1 297000000
> > > > 0 0 50000
> > > > hdmi 0 0 0 297000000
> > > > 0 0 50000
> > > > tcon1 0 0 0 297000000
> > > > 0 0 50000
> > > > pll-mipi 1 1 1 178200000
> > > > 0 0 50000
> > > > tcon0 2 2 1 178200000
> > > > 0 0 50000
> > > > tcon-pixel-clock 1 1 1 29700000
> > > > 0 0 50000
> > > > pll-video0-2x 0 0 0 594000000
> > > > 0 0 50000
> > >
> > > This discussion is going nowhere. I'm telling you that your patch
> > > doesn't apply the divider you want on the proper clock, and you're
> > > replying that indeed, you're applying it on the wrong clock.
> > >
> > > It might work by accident in your case, but the board I have here
> > > clearly indicates otherwise, so there's two possible way out here:
> > >
> > > - Either you apply that divider to the TCON *module* clock, and not
> > > the dclk
> > >
> > > - Or you point to somewhere in the allwinner code where the bpp /
> > > lanes divider is used for the dclk divider.
> >
> > I don't know how to proceed further on this, as you say it might work
> > in accident but I have tested this in A33, A64 and R40 with 4
> > different DSI panels and one DSI-RGB bridge. All of them do use
> > PLL_MIPI (pll_rate) and it indeed depends on bpp/lanes
> >
> > 4-lane, 24-bit: Novatek NT35596 panel
> > 4-lane, 24-bit: Feiyang, FY07024di26a30d panel
> > 4-lane, 24-bit: Bananapi-s070wv20 panel
> > 2-lane, 24-bit: Techstar,ts8550b panel
> >
> > and
> >
> > 4-lane, 24-bit, ICN6211 DSI-to-RGB bridge panel
> >
> > All above listed panels and bridges are working as per BSP and do
> > follow bpp/lanes and for DIVIDER 4 no panel is working.
>
> Look. I'm not saying that there's no issue, I'm saying that your
> patch, applied to the clock you're applying it to, doesn't make sense
> and isn't what the BSP does.

tcon-pixel clock is the rate that you want to achive on display side and
if you have 4 lanes 32bit or lanes and different bit number that you need
to have a clock that is able to put outside bits and speed equal to
pixel-clock * bits / lanes. so If you want a pixel-clock of 40 mhz
and you have 32bits and 4 lanes you need to have a clock of
40 * 32 / 4 in no-burst mode. I think that this is done but most of the display.
Now in burst mode I don't know how should work the calculation of the
clock for the
require bandwidth and even I understand your comment I would like to have your
clock tree after you boot on the display side and if it is possible I
want to assemble a kit
like you have.

>
> You can keep on arguing that your patch is perfect as is, but the fact
> that there's regressions proves otherwise.
>

Well when you push your code you said that you have tested on more
then one display.
Can I know where are the others?

> > The panels/bridges I have has tested in BSP and as you mentioned in

> > another mail, your panel is not tested in BSP - this is the only
> > difference. I did much reverse-engineering on PLL_MIPI clocking in BSP
> > so I'm afraid what can I do next on this, If you want to look further
> > on BSP I would suggest to verify on pll_rate side. If you feel
> > anything I'm missing please let me know.
>
> I already told you how we can make some progress in the mail you
> quoted, but you chose to ignore that.
>

Yes, the idea is to make progress. Thank you about your helping

Michael

> Until there's been some progress on either points mentionned above,
> I'm just going to stop answering on this topic.
>
> Maxime
>
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com



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