linux-kernel - Re: [PATCH RFC 1/8] drm/bridge: dw-hdmi: Add SCDC and TMDS Scrambling support

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Message-ID: <18593437.RcPPLLf6y1@avalon>
Date:   Fri, 23 Nov 2018 16:33:18 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     architt@...eaurora.org, a.hajda@...sung.com,
        dri-devel@...ts.freedesktop.org, linux-amlogic@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Nickey Yang <nickey.yang@...k-chips.com>,
        Huicong Xu <xhc@...k-chips.com>
Subject: Re: [PATCH RFC 1/8] drm/bridge: dw-hdmi: Add SCDC and TMDS Scrambling support

Hi Neil,

On Friday, 23 November 2018 16:29:15 EET Neil Armstrong wrote:
> On 23/11/2018 15:25, Laurent Pinchart wrote:
> > On Friday, 23 November 2018 16:02:14 EET Neil Armstrong wrote:
> >> Add support for SCDC Setup for TMDS Clock > 3.4GHz and enable TMDS
> >> Scrambling when supported or mandatory.
> >> 
> >> This patch also adds an helper to setup the control bit to support
> >> the hight TMDS Bit Period/TMDS Clock-Period Ratio as required with
> > 
> > s/hight/high/ ?
> 
> Thanks for catching !
> 
> >> TMDS Clock > 3.4GHz for HDMI2.0 3840x2160@...50 modes.
> > 
> > Why do you need a helper for this, is there no way it could be handled
> > internally ?
> 
> I could, but all the platforms would also do it internally... seems better
> to have common helper, no ? And it will be usable by the PHY models handler
> in the dw-hdmi driver aswell.

I meant internally in the dw-hdmi driver, not in the glue layer.

> >> These changes were based on work done by Huicong Xu <xhc@...k-chips.com>
> >> and Nickey Yang <nickey.yang@...k-chips.com> to support HDMI2.0 modes
> >> on the Rockchip 4.4 BSP kernel at [1]
> >> 
> >> [1] https://github.com/rockchip-linux/kernel/tree/release-4.4
> >> 
> >> Cc: Nickey Yang <nickey.yang@...k-chips.com>
> >> Cc: Huicong Xu <xhc@...k-chips.com>
> >> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
> >> ---
> >> 
> >>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 45 +++++++++++++++++++++--
> >>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.h |  1 +
> >>  include/drm/bridge/dw_hdmi.h              |  1 +
> >>  3 files changed, 44 insertions(+), 3 deletions(-)
> >> 
> >> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> >> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c index
> >> 5971976284bf..523508af70b0 100644
> >> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> >> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c

[snip]

> >> @@ -1562,6 +1581,26 @@ static void hdmi_av_composer(struct dw_hdmi *hdmi,
> >>  		vsync_len /= 2;
> >>  	}
> >> 
> >> +	/* Scrambling Control */
> >> +	if (hdmi_info->scdc.supported) {
> >> +		if (vmode->mpixelclock > 340000000 ||
> >> +		    hdmi_info->scdc.scrambling.low_rates) {
> >> +			drm_scdc_readb(&hdmi->i2c->adap, SCDC_SINK_VERSION,
> >> +				       &bytes);
> >> +			drm_scdc_writeb(&hdmi->i2c->adap, SCDC_SOURCE_VERSION,
> >> +					bytes);
> > 
> > Shouldn't the source version be min(sink version, highest supported source
> > version) ?
> 
> How should the "highest supported source version" be defined ?

That's the highest version supported by the DW HDMI TX controller, and is an 
intrinsic property of the IP core. With the above code, a sink newer than the 
DW HDMI TX will incorrectly be told that the source supports the same version 
as the sink.

> >> +			drm_scdc_set_scrambling(&hdmi->i2c->adap, 1);
> >> +			hdmi_writeb(hdmi, (u8)~HDMI_MC_SWRSTZ_TMDSSWRST_REQ,
> >> +				    HDMI_MC_SWRSTZ);
> >> +			hdmi_writeb(hdmi, 1, HDMI_FC_SCRAMBLER_CTRL);
> >> +		} else {
> >> +			hdmi_writeb(hdmi, 0, HDMI_FC_SCRAMBLER_CTRL);
> >> +			hdmi_writeb(hdmi, (u8)~HDMI_MC_SWRSTZ_TMDSSWRST_REQ,
> >> +				    HDMI_MC_SWRSTZ);
> >> +			drm_scdc_set_scrambling(&hdmi->i2c->adap, 0);
> >> +		}
> >> +	}
> >> +
> >>  	/* Set up horizontal active pixel width */
> >>  	hdmi_writeb(hdmi, mode->hdisplay >> 8, HDMI_FC_INHACTV1);
> >>  	hdmi_writeb(hdmi, mode->hdisplay, HDMI_FC_INHACTV0);

[snip]

-- 
Regards,

Laurent Pinchart