linux-kernel - Re: [PATCH] drm/msm/dp: delete DP_RECOVERED_CLOCK_OUT

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Date:   Mon, 1 Aug 2022 13:08:13 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     Stephen Boyd <swboyd@...omium.org>, <agross@...nel.org>,
        <airlied@...ux.ie>, <bjorn.andersson@...aro.org>,
        <daniel@...ll.ch>, <dianders@...omium.org>,
        <dmitry.baryshkov@...aro.org>, <robdclark@...il.com>,
        <sean@...rly.run>, <vkoul@...nel.org>
CC:     <quic_aravindh@...cinc.com>, <quic_sbillaka@...cinc.com>,
        <freedreno@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/dp: delete DP_RECOVERED_CLOCK_OUT_EN to fix tps4



On 8/1/2022 12:51 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-08-01 12:42:50)
>> Data Symbols scrambled is required for tps4 at link training 2.
>> Therefore SCRAMBLING_DISABLE bit should not be set for tps4 to
>> work.
>> RECOVERED_CLOCK_OUT_EN is for enable simple EYE test for jitter
>> measurement with minimal equipment for embedded applications purpose
>> and is not required to be set during normal operation.
>> Current implementation always have RECOVERED_CLOCK_OUT_EN bit set
>> which cause SCRAMBLING_DISABLE bit wrongly set at tps4 which prevent
>> tps4 from working.
>> This patch delete setting RECOVERED_CLOCK_OUT_EN to fix SCRAMBLING_DISABLE
>> be wrongly set at tps4.
>>
>> Fixes: 956653250b21 ("drm/msm/dp: add support of tps4 (training pattern 4) for HBR3")
>>
>> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
>> ---
>>   drivers/gpu/drm/msm/dp/dp_ctrl.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> index ab6aa13..013ca02 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> @@ -1214,7 +1214,7 @@ static int dp_ctrl_link_train_2(struct dp_ctrl_private *ctrl,
>>          if (ret)
>>                  return ret;
>>
>> -       dp_ctrl_train_pattern_set(ctrl, pattern | DP_RECOVERED_CLOCK_OUT_EN);
>> +       dp_ctrl_train_pattern_set(ctrl, pattern);
> This line is from the first patch introducing this driver. Even if this
> is fixing tps4 support, it sounds like the bit should never have been
> enabled in the first place. Why isn't the fixes tag targeted at the
> first commit? Does it hurt to apply it without commit 956653250b21?
agree, it should be fixed to first patch