[PATCH] drm/rockchip: Update crtc fixup to account for fractional clk change
Chris Morgan
macromorgan at hotmail.com
Thu Sep 16 11:45:17 PDT 2021
On Thu, Sep 16, 2021 at 10:08:05AM -0700, Doug Anderson wrote:
> Hi,
>
> On Tue, Sep 14, 2021 at 4:14 AM Heiko Stübner <heiko at sntech.de> wrote:
> >
> > Hi,
> >
> > Am Mittwoch, 8. September 2021, 15:53:56 CEST schrieb Chris Morgan:
> > > From: Chris Morgan <macromorgan at hotmail.com>
> > >
> > > After commit 928f9e268611 ("clk: fractional-divider: Hide
> > > clk_fractional_divider_ops from wide audience") was merged it appears
> > > that the DSI panel on my Odroid Go Advance stopped working. Upon closer
> > > examination of the problem, it looks like it was the fixup in the
> > > rockchip_drm_vop.c file was causing the issue. The changes made to the
> > > clk driver appear to change some assumptions made in the fixup.
> > >
> > > After debugging the working 5.14 kernel and the no-longer working
> > > 5.15 kernel, it looks like this was broken all along but still
> > > worked, whereas after the fractional clock change it stopped
> > > working despite the issue (it went from sort-of broken to very broken).
> > >
> > > In the 5.14 kernel the dclk_vopb_frac was being requested to be set to
> > > 17000999 on my board. The clock driver was taking the value of the
> > > parent clock and attempting to divide the requested value from it
> > > (17000000/17000999 = 0), then subtracting 1 from it (making it -1),
> > > and running it through fls_long to get 64. It would then subtract
> > > the value of fd->mwidth from it to get 48, and then bit shift
> > > 17000999 to the left by 48, coming up with a very large number of
> > > 7649082492112076800. This resulted in a numerator of 65535 and a
> > > denominator of 1 from the clk driver. The driver seemingly would
> > > try again and get a correct 1:1 value later, and then move on.
> > >
> > > Output from my 5.14 kernel (with some printfs for good measure):
> > > [ 2.830066] rockchip-drm display-subsystem: bound ff460000.vop (ops vop_component_ops)
> > > [ 2.839431] rockchip-drm display-subsystem: bound ff450000.dsi (ops dw_mipi_dsi_rockchip_ops)
> > > [ 2.855980] Clock is dclk_vopb_frac
> > > [ 2.856004] Scale 64, Rate 7649082492112076800, Oldrate 17000999, Parent Rate 17000000, Best Numerator 65535, Best Denominator 1, fd->mwidth 16
> > > [ 2.903529] Clock is dclk_vopb_frac
> > > [ 2.903556] Scale 0, Rate 17000000, Oldrate 17000000, Parent Rate 17000000, Best Numerator 1, Best Denominator 1, fd->mwidth 16
> > > [ 2.903579] Clock is dclk_vopb_frac
> > > [ 2.903583] Scale 0, Rate 17000000, Oldrate 17000000, Parent Rate 17000000, Best Numerator 1, Best Denominator 1, fd->mwidth 16
> > >
> > > Contrast this with 5.15 after the clk change where the rate of 17000999
> > > was getting passed and resulted in numerators/denomiators of 17001/
> > > 17000.
> > >
> > > Output from my 5.15 kernel (with some printfs added for good measure):
> > > [ 2.817571] rockchip-drm display-subsystem: bound ff460000.vop (ops vop_component_ops)
> > > [ 2.826975] rockchip-drm display-subsystem: bound ff450000.dsi (ops dw_mipi_dsi_rockchip_ops)
> > > [ 2.843430] Rate 17000999, Parent Rate 17000000, Best Numerator 17018, Best Denominator 17017
> > > [ 2.891073] Rate 17001000, Parent Rate 17000000, Best Numerator 17001, Best Denominator 17000
> > > [ 2.891269] Rate 17001000, Parent Rate 17000000, Best Numerator 17001, Best Denominator 17000
> > > [ 2.891281] Rate 17001000, Parent Rate 17000000, Best Numerator 17001, Best Denominator 17000
> > >
> > > After tracing through the code it appeared that this function here was
> > > adding a 999 to the requested frequency because of how the clk driver
> > > was rounding/accepting those frequencies. I believe after the changes
> > > made in the commit listed above the assumptions listed in this driver
> > > are no longer true. When I remove the + 999 from the driver the DSI
> > > panel begins to work again.
> > >
> > > Output from my 5.15 kernel with 999 removed (printfs added):
> > > [ 2.852054] rockchip-drm display-subsystem: bound ff460000.vop (ops vop_component_ops)
> > > [ 2.864483] rockchip-drm display-subsystem: bound ff450000.dsi (ops dw_mipi_dsi_rockchip_ops)
> > > [ 2.880869] Clock is dclk_vopb_frac
> > > [ 2.880892] Rate 17000000, Parent Rate 17000000, Best Numerator 1, Best Denominator 1
> > > [ 2.928521] Clock is dclk_vopb_frac
> > > [ 2.928551] Rate 17000000, Parent Rate 17000000, Best Numerator 1, Best Denominator 1
> > > [ 2.928570] Clock is dclk_vopb_frac
> > > [ 2.928574] Rate 17000000, Parent Rate 17000000, Best Numerator 1, Best Denominator 1
> > >
> > > I have tested the change extensively on my Odroid Go Advance (Rockchip
> > > RK3326) and it appears to work well. However, this change will affect
> > > all Rockchip SoCs that use this driver so I believe further testing
> > > is warranted. Please note that without this change I can confirm
> > > at least all PX30s with DSI panels will stop working with the 5.15
> > > kernel.
> > >
> > > Signed-off-by: Chris Morgan <macromorgan at hotmail.com>
> >
> > With 5.15-rc1 on:
> > - rk3288-pinky+eDP (was working -> still working)
> > - rk3399-kevin+eDP (was working -> still working)
> > - px30-minievb (was broken -> working again)
> >
> > Tested-by: Heiko Stuebner <heiko at sntech.de>
> >
> >
> > I've also added Doug, maybe he remembers some historic artifact
> > to keep in mind about the original patch.
>
> So when you say "was working" -> "still working", how did you test
> that? Did you just confirm that something was showing up on the
> screen, or did you check debugfs and make sure that the PLLs were all
> being set correctly? Also, I can't quite remember if the problems here
> were related to the internal display (and on which rockchip device) or
> HDMI where we could have a whole lot more possible pixel clocks. I can
> dig if need be. ...but I'm fairly certain that we can't just delete
> the "+ 999" and expect everything to work. All of the stuff in the
> comment above the "+ 999" is still as true today as it was when I
> wrote it. DRM is still in kHz and the Rockchip clock driver still
> rounds down.
>
> I suspect that the problem here is that the logic I wrote up just
> doesn't work great if your display clock is made by a "frac" clock.
> That's pretty much what I was saying when I wrote the comment:
>
> > NOTE: if the PLL (maybe through a divider) could actually make
> > a clock rate 999 Hz higher instead of the one we want then this
> > could be a problem.
>
> Maybe we can come up with a solution, though.
>
> So one thing is that I'd suspect that the problem is actually a bug
> with the fractional clock driver. "Best Numerator 17001, Best
> Denominator 17000" is probably not a valid thing to set and the clock
> driver should know this and seek out a different rate. I haven't dug
> through your code paths but, for instance, the comments above
> rockchip_fractional_approximation() say that denominator must be 20x
> the numerator if you want a good clock. That's clearly not the case
> here. There could also be maximum values of the numerator /
> denominator that are being ignored. I would sorta bet that if the frac
> clock driver was fixed that a clock anywhere between 17000000 and
> 17000999 would work just fine for you.
>
> In any case, despite the clock driver being screwy, probably this
> would fix it for you (untested) and is a better solution I think:
>
> rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000);
> if (rate / 1000 != adjusted_mode->clock)
> rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000 + 999);
This appears to work for me at least. I'll resubmit a patch with this
as the solution. Thank you.
>
> Basically: if we can happen to make the rate exactly then we're good.
> Otherwise then try bumping up by 999.
>
>
> > > ---
> > > drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 21 +++------------------
> > > 1 file changed, 3 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > > index ba9e14da41b4..bfef4f52dce6 100644
> > > --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > > @@ -1169,31 +1169,16 @@ static bool vop_crtc_mode_fixup(struct drm_crtc *crtc,
> > > *
> > > * - DRM works in in kHz.
> > > * - Clock framework works in Hz.
> > > - * - Rockchip's clock driver picks the clock rate that is the
> > > - * same _OR LOWER_ than the one requested.
> > > *
> > > * Action plan:
> > > *
> > > - * 1. When DRM gives us a mode, we should add 999 Hz to it. That way
> > > - * if the clock we need is 60000001 Hz (~60 MHz) and DRM tells us to
> > > - * make 60000 kHz then the clock framework will actually give us
> > > - * the right clock.
> > > - *
> > > - * NOTE: if the PLL (maybe through a divider) could actually make
> > > - * a clock rate 999 Hz higher instead of the one we want then this
> > > - * could be a problem. Unfortunately there's not much we can do
> > > - * since it's baked into DRM to use kHz. It shouldn't matter in
> > > - * practice since Rockchip PLLs are controlled by tables and
> > > - * even if there is a divider in the middle I wouldn't expect PLL
> > > - * rates in the table that are just a few kHz different.
> > > - *
> > > - * 2. Get the clock framework to round the rate for us to tell us
> > > + * 1. Get the clock framework to round the rate for us to tell us
> > > * what it will actually make.
> > > *
> > > - * 3. Store the rounded up rate so that we don't need to worry about
> > > + * 2. Store the rounded up rate so that we don't need to worry about
> > > * this in the actual clk_set_rate().
> > > */
> > > - rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000 + 999);
> > > + rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000);
> > > adjusted_mode->clock = DIV_ROUND_UP(rate, 1000);
> > >
> > > return true;
> > >
> >
> >
> >
> >
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