Re: [PATCH] media: arch: sh: migor: Fix TW9910 PDN gpio

[jacopo mondi <jacopo@jmondi.org>]

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Hi Laurent, Geert,

On Wed, May 30, 2018 at 02:52:31PM +0300, Laurent Pinchart wrote:
> Hi Geert,
>
> On Wednesday, 30 May 2018 12:30:49 EEST Geert Uytterhoeven wrote:
> > Hi Jacopo,
> >
> > On Wed, May 30, 2018 at 11:13 AM, Jacopo Mondi wrote:
> > > The TW9910 PDN gpio (power down) is listed as active high in the chip
> > > manual. It turns out it is actually active low as when set to physical
> > > level 0 it actually turns the video decoder power off.
> >
> > So the picture "Typical TW9910 External Circuitry" in the datasheet, which
> > ties PDN to GND permanently, is wrong?

Also the definition of PDN pin in TW9910 manual, as reported by Laurent made me
think the pin had to stay in logical state 1 to have the chip powered
down. That's why my initial 'ACTIVE_HIGH' flag. The chip was not
recognized, but I thought it was a local problem of the Migo-R board I
was using.

Then one day I tried inverting the pin active state just to be sure,
and it started being fully operational :/

>
> The SH PTT2 line is connected directory to the TW9910 PDN signal, without any
> inverter on the board. The PDN signal is clearly documented as active-high in
> the TW9910 datasheet. Something is thus weird.

I suspect the 'active high' definition in datasheet is different from
our understanding. Their 'active' means the chip is operational, which
is not what one would expect from a powerdown pin.

>
> Jacopo, is it possible to measure the PDN signal on the board as close as
> possible to the TW9910 to see if it works as expected ?

Not for me. The board is in Japan and my multimeter doesn't have cables
that long, unfortunately.

Thanks
   j

>
> --
> Regards,
>
> Laurent Pinchart
>
>
>

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