Re: [linux-sunxi] Re: [PATCH v2 11/27] drm/sun4i: tcon: Add support for tcon-top gate

[Jernej Åkrabec]

Dne Äetrtek, 21. junij 2018 ob 17:35:45 CEST je Jernej Åkrabec napisal(a):
> Dne Äetrtek, 21. junij 2018 ob 03:23:27 CEST je Chen-Yu Tsai napisal(a):
> > On Thu, Jun 21, 2018 at 3:37 AM, Jernej Åkrabec <jernej.skrabec@xxxxxxxx>
> 
> wrote:
> > > Dne sobota, 16. junij 2018 ob 07:48:38 CEST je Chen-Yu Tsai napisal(a):
> > >> On Sat, Jun 16, 2018 at 1:33 AM, Jernej Åkrabec
> > >> <jernej.skrabec@xxxxxxxx>
> > > 
> > > wrote:
> > >> > Dne petek, 15. junij 2018 ob 19:13:17 CEST je Chen-Yu Tsai 
napisal(a):
> > >> >> On Sat, Jun 16, 2018 at 12:41 AM, Jernej Åkrabec
> > >> >> 
> > >> >> <jernej.skrabec@xxxxxxxx> wrote:
> > >> >> > Hi,
> > >> >> > 
> > >> >> > Dne petek, 15. junij 2018 ob 10:31:10 CEST je Maxime Ripard
> 
> napisal(a):
> > >> >> >> Hi,
> > >> >> >> 
> > >> >> >> On Tue, Jun 12, 2018 at 10:00:20PM +0200, Jernej Skrabec wrote:
> > >> >> >> > TV TCONs connected to TCON TOP have to enable additional gate
> > >> >> >> > in
> > >> >> >> > order
> > >> >> >> > to work.
> > >> >> >> > 
> > >> >> >> > Add support for such TCONs.
> > >> >> >> > 
> > >> >> >> > Signed-off-by: Jernej Skrabec <jernej.skrabec@xxxxxxxx>
> > >> >> >> > ---
> > >> >> >> > 
> > >> >> >> >  drivers/gpu/drm/sun4i/sun4i_tcon.c | 11 +++++++++++
> > >> >> >> >  drivers/gpu/drm/sun4i/sun4i_tcon.h |  4 ++++
> > >> >> >> >  2 files changed, 15 insertions(+)
> > >> >> >> > 
> > >> >> >> > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > >> >> >> > b/drivers/gpu/drm/sun4i/sun4i_tcon.c index
> > >> >> >> > 08747fc3ee71..0afb5a94a414
> > >> >> >> > 100644
> > >> >> >> > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > >> >> >> > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > >> >> >> > @@ -688,6 +688,16 @@ static int sun4i_tcon_init_clocks(struct
> > >> >> >> > device
> > >> >> >> > *dev,
> > >> >> >> > 
> > >> >> >> >             dev_err(dev, "Couldn't get the TCON bus clock\n");
> > >> >> >> >             return PTR_ERR(tcon->clk);
> > >> >> >> >     
> > >> >> >> >     }
> > >> >> >> > 
> > >> >> >> > +
> > >> >> >> > +   if (tcon->quirks->has_tcon_top_gate) {
> > >> >> >> > +           tcon->top_clk = devm_clk_get(dev, "tcon-top");
> > >> >> >> > +           if (IS_ERR(tcon->top_clk)) {
> > >> >> >> > +                   dev_err(dev, "Couldn't get the TCON TOP bus
> > >> >> >> > clock\n");
> > >> >> >> > +                   return PTR_ERR(tcon->top_clk);
> > >> >> >> > +           }
> > >> >> >> > +           clk_prepare_enable(tcon->top_clk);
> > >> >> >> > +   }
> > >> >> >> > +
> > >> >> >> 
> > >> >> >> Is it required for the TCON itself to operate, or does the TCON
> > >> >> >> requires the TCON TOP, which in turn requires that clock to be
> > >> >> >> functional?
> > >> >> >> 
> > >> >> >> I find it quite odd to have a clock that isn't meant for a
> > >> >> >> particular
> > >> >> >> device to actually be wired to another device. I'm not saying
> > >> >> >> this
> > >> >> >> isn't the case, but it would be a first.
> > >> >> > 
> > >> >> > Documentation doesn't say much about that gate. I did few tests
> > >> >> > and
> > >> >> > TCON
> > >> >> > registers can be read and written even if TCON TOP TV TCON gate is
> > >> >> > disabled. However, there is no image, as expected.
> > >> >> 
> > >> >> The R40 manual does include it in the diagram, on page 504. There's
> > >> >> also
> > >> >> a
> > >> >> mux to select whether the clock comes directly from the CCU or the
> > >> >> TV
> > >> >> encoder (a feedback mode?). I assume this is the gate you are
> > >> >> referring
> > >> >> to
> > >> >> here, in which case it is not a bus clock, but rather the TCON
> > >> >> module
> > >> >> or
> > >> >> channel clock, strangely routed.
> > >> >> 
> > >> >> > More interestingly, I enabled test pattern directly in TCON to
> > >> >> > eliminate
> > >> >> > influence of the mixer. As soon as I disabled that gate, test
> > >> >> > pattern
> > >> >> > on
> > >> >> > HDMI screen was gone, which suggest that this gate influences
> > >> >> > something
> > >> >> > inside TCON.
> > >> >> > 
> > >> >> > Another test I did was that I moved enable/disable gate code to
> > >> >> > sun4i_tcon_channel_set_status() and it worked just as well.
> > >> >> > 
> > >> >> > I'll ask AW engineer what that gate actually does, but from what I
> > >> >> > saw,
> > >> >> > I
> > >> >> > would say that most appropriate location to enable/disable TCON
> > >> >> > TOP
> > >> >> > TV
> > >> >> > TCON
> > >> >> > gate is TCON driver. Alternatively, TCON TOP driver could check if
> > >> >> > any
> > >> >> > TV
> > >> >> > TCON is in use and enable appropriate gate. However, that doesn't
> > >> >> > sound
> > >> >> > right to me for some reason.
> > >> >> 
> > >> >> If what I said above it true, then yes, the appropriate location to
> > >> >> enable
> > >> >> it is the TCON driver, but moreover, the representation of the clock
> > >> >> tree
> > >> >> should be fixed such that the TCON takes the clock from the TCON TOP
> > >> >> as
> > >> >> its
> > >> >> channel/ module clock instead. That way you don't need this patch,
> > >> >> but
> > >> >> you'd add another for all the clock routing.
> > >> > 
> > >> > Can you be more specific? I not sure what you mean here.
> > >> 
> > >> For clock related properties in the device tree:
> > >> 
> > >> &tcon_top {
> > >> 
> > >>     clocks = <&ccu CLK_BUS_TCON_TOP>,
> > >>     
> > >>              <&ccu CLK_TCON_TV0>,
> > >>              <&tve0>,
> > >>              <&ccu CLK_TCON_TV1>,
> > >>              <&tve1>;
> > >>     
> > >>     clock-names = "bus", "tcon-tv0", "tve0", "tcon-tv1", "tve1";
> > >>     clock-output-names = "tcon-top-tv0", "tcon-top-tv1";
> > >> 
> > >> };
> > >> 
> > >> &tcon_tv0 {
> > >> 
> > >>     clocks = <&ccu CLK_BUS_TCON_TV0>, <&tcon_top 0>'
> > >>     clock-names = "ahb", "tcon-ch1";
> > >> 
> > >> };
> > >> 
> > >> A diagram would look like:
> > >>                    | This part is TCON TOP |
> > >>                    
> > >>                    v                       v
> > >> 
> > >> CCU CLK_TCON_TV0 --|----\                  |
> > >> 
> > >>                    |     mux ---- gate ----|-- TCON_TV0
> > >> 
> > >> TVE0 --------------|----/                  |
> > >> 
> > >> And the same goes for TCON_TV1 and TVE1.
> > >> 
> > >> The user manual is a bit lacking on how TVE outputs a clock though.
> > > 
> > > I didn't yet received any response on HW details from AW till now, but I
> > > would like to post new version of patches soon.
> > > 
> > > While chaining like you described could be implemented easily, I don't
> > > think it really represents HW as it is. Tests showed that these two
> > > clocks are independent, otherwise register writes/reads wouldn't be
> > > possible with tcon- top gate disabled. I chose tcon-top bus clock as a
> > > parent becase if it is not enabled, it simply won't work.
> > 
> > AFAIK with the TCONs, even when the TCON channel clock (not the bus clock)
> > is disabled, register accesses still work.
> 
> You're right, I just tested that.
> 
> > I'm saying that the TCON TOP
> > gate is downstream from the TCON channel clock in the CCU. These are not
> > related to the TCON bus clock in the CCU, which affects register access.
> > 
> > Did Allwinner provide any information regarding the hierarchy of the
> > clocks?
> No reponse for now.
> 
> > > However, if everyone feels chaining is the best way to implement it,
> > > I'll
> > > do it.
> > 
> > I would like to get it right and match actual hardware. My proposal is
> > based on my understanding from the diagrams in the user manual.
> 
> So for now, your explanation is the most reasonable. Should we go ahead and
> implement your idea?
> 
> Please note that H6 has TCON-TOP too, but it has only one LCD TCON and one
> TV TCON instead of two of each kind. That means we will have hole in
> indices (tcon_lcd0 is 1, tcon_tv0 is 3, which is aligned with R40) and
> different TCON- TOP binding (no tcon_tv1 channel clock), but setup is
> exactly the same.

I just noticed issue with this proposal. If we have following clock chain for 
HDMI, everythings is ok:

TCON-TV0 -> TCON-TOP-TV0

TCON TV sets TCON-TOP-TV0 clock rate, which in turn sets TCON-TV0 clock and 
everything works.

However, when TVE will be configured, it would look like this:

TVE0 -> TCON-TOP-TV0

TVE driver will set TVE0 clock to 216 MHz and TCON TV would set TCON-TOP-TV0 
rate which in turn sets TVE0 clock to something like 13.5 MHz (or whatever is 
the right clock rate for PAL and NTSC). As you can see, same clock is set to 
two different rates by two different drivers.

It *might* still work, since encoders set clock rate after TCON (at least that 
is my experience for HDMI pipeline), but that is still wrong.

To overcome above issue, I would stick to original proposal with additional 
clock specified in TCON TV DT node. That way TCON driver would always set 
clock rate to TCON-TV0 clock. If TVE0 is enabled, TCON wouldn't interfere with 
setting clock rate, because TCON-TV0 clock would be decoupled in TCON-TOP mux.

What do you think?

Best regards,
Jernej