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From: Saurabh Anand <saurabh.anand@oss.qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>,
	Vinod Koul <vkoul@kernel.org>,
	Neil Armstrong <neil.armstrong@linaro.org>,
	Manivannan Sadhasivam <mani@kernel.org>,
	Rob Clark <robin.clark@oss.qualcomm.com>,
	Dmitry Baryshkov <lumag@kernel.org>,
	Abhinav Kumar <abhinav.kumar@linux.dev>,
	Jessica Zhang <jesszhan0024@gmail.com>,
	Sean Paul <sean@poorly.run>,
	Marijn Suijten <marijn.suijten@somainline.org>,
	David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>
Cc: linux-arm-msm@vger.kernel.org, linux-phy@lists.infradead.org,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	freedreno@lists.freedesktop.org,
	Ritesh Kumar <quic_riteshk@quicinc.com>,
	Vishnuvardhan Prodduturi <quic_vproddut@quicinc.com>,
	Mani Chandana Kuntumalla <quic_mkuntuma@quicinc.com>,
	Mahadevan P <mahadevan.p@oss.qualcomm.com>
Subject: Re: [PATCH 3/4] drm/msm/dp: skip LTTPR init when no LTTPRs are present
Date: Mon, 7 Sep 2026 15:14:33 +0530	[thread overview]
Message-ID: <fa897e53-2ebe-4322-bf73-98788854083d@oss.qualcomm.com> (raw)
In-Reply-To: <315db50d-6553-412d-8fca-a4b4441f881b@oss.qualcomm.com>


On 24-08-2026 18:45, Konrad Dybcio wrote:
> On 8/24/26 1:28 PM, Saurabh Anand wrote:
>> drm_dp_lttpr_count() returns 0 when no LTTPRs are detected and a
>> negative value on error. The previous code passed the result directly
>> to drm_dp_lttpr_init() without checking, which would call into the
>> LTTPR transparency-mode setup with a zero or negative repeater count.
>>
>> Add an early return for lttpr_count <= 0 to skip the init entirely
>> when there are no repeaters in the link, matching the expected usage
>> of drm_dp_lttpr_init().
> Reading the body of that function, I'm not sure your statement is true

drm_dp_lttpr_count() returns 0 when no LTTPRs are detected and a
negative error code when the LTTPR common capabilities report an invalid
or unsupported repeater count.

drm_dp_lttpr_init() already handles the zero-count case by returning
early. However, when passed a negative count, it still writes transparent
mode before returning -ENODEV.

I will update the commit message giving more details.

>
> Konrad

-- 
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  reply	other threads:[~2026-09-07  9:44 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-08-24 11:28 [PATCH 0/4] drm/msm/dp, phy: qcom: improve DP Type-C reconnect handling Saurabh Anand
2026-08-24 11:28 ` [PATCH 1/4] phy: qcom: qmp-combo: delay Type-C mux switch while DP PHY is initializing Saurabh Anand
2026-08-24 11:44   ` sashiko-bot
2026-09-02  7:48   ` Manivannan Sadhasivam
2026-09-07  9:47     ` Saurabh Anand
2026-08-24 11:28 ` [PATCH 2/4] drm/msm/dp: clear force_link_train flag when link training succeeds Saurabh Anand
2026-08-24 11:40   ` sashiko-bot
2026-08-24 13:17   ` Konrad Dybcio
2026-09-07  9:35     ` Saurabh Anand
2026-08-24 11:28 ` [PATCH 3/4] drm/msm/dp: skip LTTPR init when no LTTPRs are present Saurabh Anand
2026-08-24 11:35   ` sashiko-bot
2026-08-24 13:15   ` Konrad Dybcio
2026-09-07  9:44     ` Saurabh Anand [this message]
2026-08-24 11:28 ` [PATCH 4/4] drm/msm/dp: continue link training downgrade when cable is still plugged Saurabh Anand
2026-08-24 11:40   ` sashiko-bot

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