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

[Chen-Yu Tsai]

On Thu, Jun 21, 2018 at 3:37 AM, Jernej Škrabec <jernej.skrabec at siol.net> 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 Škrabec <jernej.skrabec at siol.net>
> 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 Škrabec
>> >>
>> >> <jernej.skrabec at siol.net> 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 at siol.net>
>> >> >> > ---
>> >> >> >
>> >> >> >  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. 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?

> 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.

Regards
ChenYu