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Wed, 27 May 2026 13:50:27 -0700 (PDT) Message-ID: Date: Thu, 28 May 2026 08:50:20 +1200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/6] drm/msm/dp: Limit voltage swing level to 2 for RA620 bridge To: Konrad Dybcio , linux-arm-msm@vger.kernel.org Cc: andersson@kernel.org, konradybcio@kernel.org, robin.clark@oss.qualcomm.com, lumag@kernel.org, abhinav.kumar@linux.dev, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260522060645.4399-1-graham.oconnor@gmail.com> <20260522060645.4399-4-graham.oconnor@gmail.com> <7e435e8c-ba0e-453a-b95c-450446dfc0ff@oss.qualcomm.com> Content-Language: en-GB, en-US From: Gekko In-Reply-To: <7e435e8c-ba0e-453a-b95c-450446dfc0ff@oss.qualcomm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Konrad I completely agree. This patch is a temporary hardware workaround for RA620 bridge support and should not have been submitted. Please disregard. Graham On 22/05/2026 21:28, Konrad Dybcio wrote: > On 5/22/26 8:06 AM, Graham O'Connor wrote: >> The RA620 DP-to-HDMI bridge used on the Radxa Dragon Q6A does not >> acknowledge DP link training at voltage swing level 3. The bridge >> requests maximum voltage swing but never completes link training >> when the driver attempts level 3, causing HDMI output to fail. >> >> Cap DP_TRAIN_LEVEL_MAX at 2 to match the behaviour of the vendor >> kernel, where link training completes successfully at level 2. >> This allows the RA620 bridge to establish a stable HDMI connection. >> >> Tested on Radxa Dragon Q6A (QCS6490) with RA620 DP-to-HDMI bridge >> >> Signed-off-by: Graham O'Connor >> --- >> drivers/gpu/drm/msm/dp/dp_link.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/msm/dp/dp_link.h b/drivers/gpu/drm/msm/dp/dp_link.h >> index 76125e9c0..ff0d8e99d 100644 >> --- a/drivers/gpu/drm/msm/dp/dp_link.h >> +++ b/drivers/gpu/drm/msm/dp/dp_link.h >> @@ -24,7 +24,7 @@ struct msm_dp_link_info { >> unsigned long capabilities; >> }; >> >> -#define DP_TRAIN_LEVEL_MAX 3 >> +#define DP_TRAIN_LEVEL_MAX 2 > > You're limiting this value for *all* devices featuring a Qualcomm > SoC with a DP controller. Instead, if this is really an issue that > results from the bridge's capabilities (which could potentially only > be a symptom, not the cause), this should be somehow limited to the > specific bridge itself > > Konrad