Date:   Wed, 5 Jun 2019 13:03:16 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Chen-Yu Tsai <wens@...e.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-amarula <linux-amarula@...rulasolutions.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v6 11/22] clk: sunxi-ng: a64: Add minimum rate for PLL_MIPI

On Wed, Jun 5, 2019 at 12:19 PM Maxime Ripard <maxime.ripard@...tlin.com> 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

>
> > > 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 your patches, you're using the bpp / lanes divider on the TCON
> dotclock, ie, the wrong clock.
>
> Again, I'm not saying that my analysis of the source code is correct
> here. But you haven't said anything to prove it's wrong either.

Don't understand what proves are remaining, I have explained each line
from BSP and saying pll rate is depends on dsi_div which is bpp/lanes
not wrt tcon_div on BSP (which is set to default 4) and which indeed
verified in A33, R40. all the code using bpp/lanes.

Please let me know if you need any more information to look?

[1] https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L805

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