[02/11] video: ARM CLCD: support DT signal inversion flags
Ray Jui
ray.jui at broadcom.com
Fri Feb 19 17:23:33 PST 2016
Hi Linus,
On 2/19/2016 12:46 AM, Linus Walleij wrote:
> On Wed, Feb 17, 2016 at 7:10 PM, Ray Jui <ray.jui at broadcom.com> wrote:
>
>> A somewhat related question, how do you see the CLKSEL bit in the TIM2
>> register will be supported in the future? There are some cases where the
>> CLKSEL bit needs to be set, and therefore the "CLCDCLK" instead of "HCLK"
>> reference clock source is selected.
>
> I think it's very simple:
>
> The DT node usually looks like so:
>
> display at 10120000 {
> compatible = "arm,pl110", "arm,primecell";
> (...)
> clocks = <&oscclk4>, <&pclk>;
> clock-names = "clcd", "apb_pclk";
>
> Just add a custom attribute pointing to the
> reference clock in this array:
>
> clcd-reference-clock = <0>;
>
> If this is set to <1> "apb_pclk" (i.e. HCLK) is
> the reference, and that bit in TIM2 gets set.
This looks good!
>
> Do you have a system that needs this?
>
Yah, we have a system (Cygnus) that can either use the HCLK, or an
external clock generated from a PLL. To get certain pixel clock
frequencies (depending on the LCD panel we use), we need to use the
external clock source with the PLL configured to a particular VCO frequency.
We have not enabled full LCD/video support on that platform in the
mainline kernel, but we'll eventually get to it.
> Yours,
> Linus Walleij
>
Thanks,
Ray
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