Re: [PATCH v6 2/3] media: i2c: adv748x: add adv748x driver

[Hans Verkuil]

On 07/03/2017 05:00 PM, Kieran Bingham wrote:
> Hi Hans,
>
> On 03/07/17 15:45, Kieran Bingham wrote:
> > Hi Hans,
> >
> > Thanks for your review,
> >
> > On 03/07/17 14:51, Hans Verkuil wrote:
> > > On 06/27/2017 05:03 PM, Kieran Bingham wrote:
> > > > From: Kieran Bingham <kieran.bingham+renesas@xxxxxxxxxxxxxxxx>
> > > >
> > > > Provide support for the ADV7481 and ADV7482.
>
> ...
>
> > > > +/* -----------------------------------------------------------------------------
> > > > + * HDMI and CP
> > > > + */
> > > > +
> > > > +#define ADV748X_HDMI_MIN_WIDTH        640
> > > > +#define ADV748X_HDMI_MAX_WIDTH        1920
> > > > +#define ADV748X_HDMI_MIN_HEIGHT        480
> > > > +#define ADV748X_HDMI_MAX_HEIGHT        1200
> > > > +#define ADV748X_HDMI_MIN_PIXELCLOCK    0        /* unknown */
> > >
> > > 0 makes no sense. Something like 13000000 would work better (pixelclock rate for
> > > V4L2_DV_BT_CEA_720X480I59_94 is 13500000).
> >
> > This is another one that must have got lost somehow - you'd already told me this
> > and I'm really sure I changed it to the value you suggested ...
> >
> > /me is confused at code loss - Must have been a rebase gone bad. :-(
> >
> >
> > > > +#define ADV748X_HDMI_MAX_PIXELCLOCK    162000000
> > >
> > > You probably based that on the 1600x1200p60 format?
> >
> > No idea I'm afraid - it's the value that was set when I recieved the driver...
> >
> > > 162MHz is a bit low for an adv receiver. The adv7604 and adv8742 have a max rate
> > > of 225 MHz.
> > > This should be documented in the datasheet.
> >
> > Hrm ... haven't found it yet - I'll keep digging....
>
>
> I've found this as the most relevant reference:
>
> ================================================================================
> The ADV7481 HDMI capable receiver supports a maximum pixel clock frequency of
> 162 MHz, allowing HDTV formats up to 1080p, and display resolutions up to UXGA
> (1600 Ã 1200 at 60 Hz). The device integrates a consumer electronics control
> (CEC) controller that supports the capability discovery and control (CDC)
> feature. The HDMI input port has dedicated 5 V detect and Hot PlugTM assert pins.
> ================================================================================
>
> So that certainly looks like 162 MHz is the correct value.
>
> > > Besides, you need a bit of margin since detected pixelclock rates can be a bit off.
>
> Does that mean you would you recommend adding 0.5 MHz to the 162 MHz in a
> similar way as the minimum, or keep at 162 MHz ?
>
> (I'm assuming stay at 162 MHz, as the 7604 is set at 225MHz)

If the datasheet states that 162 MHz is max, then it should stay that way.

It's a bit peculiar: the HDMI spec allows for some variation (0.5%?) in pixelclock
rates. So a source may actually use a pixelclock rate up to 1.005 * 162 MHz. So I have
my doubts about whether 162 MHz is really the hard limit. It's hard to test, though.

And from the point of view of the API I don't think it matters.

Regards,

	Hans