Subject: Re: [PATCH 03/11] drm/bridge/synopsys: dw-hdmi: Enable workaround for
 v1.32a
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        dri-devel@lists.freedesktop.org
Cc: Jernej Skrabec <jernej.skrabec@siol.net>,
        maxime.ripard@free-electrons.com, airlied@linux.ie,
        robh+dt@kernel.org, mark.rutland@arm.com, wens@csie.org,
        architt@codeaurora.org, a.hajda@samsung.com,
        Jose.Abreu@synopsys.com, devicetree@vger.kernel.org,
        mturquette@baylibre.com, sboyd@codeaurora.org,
        linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com,
        linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org
References: <20171230210203.24115-1-jernej.skrabec@siol.net>
 <20171230210203.24115-4-jernej.skrabec@siol.net> <3367423.0HCaRuLuz8@avalon>
From: Neil Armstrong <narmstrong@baylibre.com>
Organization: Baylibre
Message-ID: <9e9269be-fde7-7654-30c0-85a26760b9ad@baylibre.com>
Date: Tue, 9 Jan 2018 16:29:47 +0100
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Sender: linux-kernel-owner@vger.kernel.org

Hi,

I think this question is for Jose.

On 09/01/2018 13:56, Laurent Pinchart wrote:
> Hi Jernej,
> 
> Thank you for the patch.
> 
> On Saturday, 30 December 2017 23:01:55 EET Jernej Skrabec wrote:
>> Allwinner SoCs have dw hdmi controller v1.32a which exhibits same
>> magenta line issue as i.MX6Q and i.MX6DL. Enable workaround for it.

We observe the same issue on Amlogic SoCs with the dw hdmi controller v2.01a.

Rockchip seems to also use count=1 for 0x200a, 0x201a and 0x211a in
https://github.com/rockchip-linux/kernel/commit/cafa8ebd5f4df41425d6f2f61633d5bc64f20e65

Changelog is :
The issue can be worked around by issuing a TMDS software reset and
then write one of the FC registers several times. After tested, the
number of iterations of RK3399/RK3328(v2.11a), RK3368(v2.01a),
RK3288(v2.00a) is one.

Can you confirm it is necessary ?

Neil

>>
>> Tests show that one iteration is enough.
>>
>> Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
> 
> This does not break R-Car DU, so
> 
> Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
>> ---
>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c index
>> a38db40ce990..7ca14d7325b5 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> @@ -1634,9 +1634,10 @@ static void dw_hdmi_clear_overflow(struct dw_hdmi
>> *hdmi) * then write one of the FC registers several times.
>>  	 *
>>  	 * The number of iterations matters and depends on the HDMI TX revision
>> -	 * (and possibly on the platform). So far only i.MX6Q (v1.30a) and
>> -	 * i.MX6DL (v1.31a) have been identified as needing the workaround, with
>> -	 * 4 and 1 iterations respectively.
>> +	 * (and possibly on the platform). So far i.MX6Q (v1.30a), i.MX6DL
>> +	 * (v1.31a) and multiple Allwinner SoCs (v1.32a) have been identified
>> +	 * as needing the workaround, with 4 iterations for v1.30a and 1
>> +	 * iteration for others.
>>  	 */
>>
>>  	switch (hdmi->version) {
>> @@ -1644,6 +1645,7 @@ static void dw_hdmi_clear_overflow(struct dw_hdmi
>> *hdmi) count = 4;
>>  		break;
>>  	case 0x131a:
>> +	case 0x132a:
>>  		count = 1;
>>  		break;
>>  	default:
>