Re: Question regarding clocks in the DW-HDMI DT bindings

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Andy,

(CC'ing Kieran Bingham)

On Monday 28 Nov 2016 19:34:59 Andy Yan wrote:
> On 2016年11月26日 03:26, Laurent Pinchart wrote:
> > On Friday 25 Nov 2016 17:08:13 Philipp Zabel wrote:
> >> Am Freitag, den 25.11.2016, 17:45 +0200 schrieb Laurent Pinchart:
> >>> On Friday 25 Nov 2016 10:56:55 Philipp Zabel wrote:
> >>>> Am Donnerstag, den 24.11.2016, 23:16 +0200 schrieb Laurent Pinchart:
> >>>>> Hi Andy,
> >>>>> 
> >>>>> As the author of the DW-HDMI DT bindings this question is addressed to
> >>>>> you, but information from anyone is more than welcome.
> >>>>> 
> >>>>> The DT bindings specify two clocks named "iahb" and "isfr" but don't
> >>>>> describe them. While I assume that the "isfr" clock corresponds to the
> >>>>> "isfrclk" input signal of the DW HDMI, there is no "iahb" clock
> >>>>> described in the IP core datasheet.
> >>>> 
> >>>> The Table 33-1 "HDMI clocks" in the i.MX6DQ reference manual [1] lists
> >>>> iahbclk (AHB bus clock), icecclk (32 kHz CEC clock), ihclk (module
> >>>> clock) and isfrclk (27 MHz internal SFR clock).
> >>>> 
> >>>> [1]
> >>>> http://www.nxp.com/assets/documents/data/en/reference-manuals/IMX6DQRM.
> >>>> pdf
> >>>> 
> >>>>> The DW HDMI IP exposes control registers through an APB, not an AHB.
> >>>>> There is a bus clock named "iapbclk", is "iahb" just an incorrect name
> >>>>> for that clock ?
> >>>> 
> >>>> According to figure 33-3 "HDMI TX Top Level Block Diagram" the control
> >>>> interface is AMBA AHB on i.MX6. Both iahbclk and ihclk are clocked by
> >>>> ahb_clk_root on i.MX6.
> >>>> 
> >>>> Register 5 (HDMI_CONFIG1_ID) contains a few bits (confsfrdir, confi2c,
> >>>> confocp, confapb, confahb) that indicate which control interface is
> >>>> used.
> >>> 
> >>> That's interesting. The DW HDMI TX documentation I found (1.40a-ea00,
> >>> Early Adopter Edition) only has the confahb bit in that register. Do you
> >>> know which version of the IP is used in iMX.6 ? I wonder whether the
> >>> above
> >>> is a Freescale-specific modification to the IP core.
> >> 
> >> The driver reports:r
> >> 
> >> dwhdmi-imx 120000.hdmi: Detected HDMI controller 0x13:0xa:0xa0:0xc1
> >> 
> >> That is DESIGN_ID 0x13, REVISION_ID 0x0a.
> >> 
> >>> I'm also a bit puzzled by the differences in the HDMI PHY between
> >>> Freescale and Renesas. The Renesas datasheet documents three registers
> >>> only for the PHY (other might exist and be undocumented), and while they
> >>> contain fields similar to the ones documented in the Freescale
> >>> datasheet,
> >>> the exact register layouts are different.
> >> 
> >> Do you mean the HDMI_PHY_* registers in the HDMI TX register space or
> >> the separate HDMI PHY i2c registers? The PHY may very well be completely
> >> different. I think OMAP5 HDMI driver uses the same DesignWare HDMI TX as
> >> i.MX6, but not the same PHY.
> > 
> > I meant the HDMI PHY I2C registers, yes. If the PHYs are really
> > SoC-specific maybe we should move the supporting code to the platform
> > glue driver.
>
> Yes,  it's really have this case, Some Soc uses DW HDMI controller,
> but uses another  different phy. So it's worth moving the phy related
> code to soc platform glue driver.

OK, sounds like we have a plan. Kieran, here's work for you :-)

> > Would anyone happen to have access to the Synopsys HDMI TX PHY
> > documentation ?

-- 
Regards,

Laurent Pinchart

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