linux-kernel - Re: [linux-sunxi] Re: [RFC PATCH 07/11] drm: sun4i: add support for the TV encoder in H3 SoC

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Message-ID: <CAGb2v66aD=G+V75N-_nYo=dGqhxpKhadM84h9G-B34=dnDwCbg@mail.gmail.com>
Date:   Sat, 20 May 2017 09:37:53 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Jernej Škrabec <jernej.skrabec@...l.net>
Cc:     linux-sunxi <linux-sunxi@...glegroups.com>,
        Icenowy Zheng <icenowy@...c.io>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [linux-sunxi] Re: [RFC PATCH 07/11] drm: sun4i: add support for
 the TV encoder in H3 SoC

On Sat, May 20, 2017 at 2:23 AM, Jernej Škrabec <jernej.skrabec@...l.net> wrote:
> Hi,
>
> Dne petek, 19. maj 2017 ob 20:08:18 CEST je Icenowy Zheng napisal(a):
>> 于 2017年5月20日 GMT+08:00 上午2:03:30, Maxime Ripard <maxime.ripard@...e-
> electrons.com> 写到:
>> >On Thu, May 18, 2017 at 12:43:50AM +0800, Icenowy Zheng wrote:
>> >> Allwinner H3 features a TV encoder similar to the one in earlier
>> >
>> >SoCs,
>> >
>> >> but with some different points about clocks:
>> >> - It has a mod clock and a bus clock.
>> >> - The mod clock must be at a fixed rate to generate signal.
>> >
>> >Why?
>>
>> It's experiment result by Jernej.
>>
>> The clock rates in BSP kernel is also specially designed
>> (PLL_DE at 432MHz) in order to be able to feed the TVE.
>
> My experiments and search through BSP code showed that TVE seems to have
> additional fixed predivider 8. So if you want to generate 27 MHz clock, unit
> has to be feed with 216 MHz.
>
> TVE has only one PLL source PLL_DE. And since 216 MHz is a bit low for DE2,
> BSP defaults to 432 MHz for PLL_DE and use divider 2 to generate 216 MHz. This
> clock is then divided by 8 internaly to get final 27 MHz.
>
> Please note that I don't have any hard evidence to support that, only
> experimental data. However, only that explanation make sense to me.
>
> BTW, BSP H3/H5 TV driver supports only PAL and NTSC which both use 27 MHz base
> clock. Further experiments are needed to check if there is any possibility to
> have other resolutions by manipulating clocks and give other proper settings.
> I plan to do that, but not in very near future.

You only have composite video output, and those are the only 2 standard
resolutions that make any sense.

ChenYu