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[2001:14bb:ac:ffd6:501:5ae1:b167:ae27]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-54b0957ffcfsm27071e87.138.2025.03.27.10.40.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Mar 2025 10:40:10 -0700 (PDT) Message-ID: <07c48ba0-dcf5-4ece-8beb-f225652c5014@oss.qualcomm.com> Date: Thu, 27 Mar 2025 19:40:07 +0200 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 v2] drm/dp: fallback to minimum when PWM bit count is zero To: Christopher Obbard , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, Johan Hovold , Rui Miguel Silva , Abel Vesa References: <20250327-wip-obbardc-qcom-t14s-oled-panel-brightness-v2-1-16dc3ee00276@linaro.org> Content-Language: en-US From: Dmitry Baryshkov In-Reply-To: <20250327-wip-obbardc-qcom-t14s-oled-panel-brightness-v2-1-16dc3ee00276@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-ORIG-GUID: lGKnaVWtKyvTBPHwJYz4J_zysmE0Nc2J X-Proofpoint-GUID: lGKnaVWtKyvTBPHwJYz4J_zysmE0Nc2J X-Authority-Analysis: v=2.4 cv=Q43S452a c=1 sm=1 tr=0 ts=67e58d7d cx=c_pps a=qKBjSQ1v91RyAK45QCPf5w==:117 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=Vs1iUdzkB0EA:10 a=VwQbUJbxAAAA:8 a=KKAkSRfTAAAA:8 a=8uZFVrZtLw_Y6pPcPrcA:9 a=QEXdDO2ut3YA:10 a=NFOGd7dJGGMPyQGDc5-O:22 a=cvBusfyB2V15izCimMoJ:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1095,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-03-27_03,2025-03-26_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 impostorscore=0 lowpriorityscore=0 bulkscore=0 spamscore=0 suspectscore=0 adultscore=0 mlxlogscore=999 malwarescore=0 mlxscore=0 priorityscore=1501 clxscore=1015 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2502280000 definitions=main-2503270120 On 27/03/2025 19:25, Christopher Obbard wrote: > According to the eDP specification (e.g., VESA eDP 1.4b, section 3.3.10.2), > if DP_EDP_PWMGEN_BIT_COUNT is less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, > the sink is required to use the MIN value as the effective bit count. > > Some eDP panels report DP_EDP_PWMGEN_BIT_COUNT as 0 while still providing > valid non-zero MIN and MAX capability values. This patch updates the logic > to use the CAP_MIN value in such cases, ensuring correct scaling of AUX-set > backlight brightness values. > > This improves compatibility with panels like the Samsung ATNA40YK20 used > on the Lenovo T14s Gen6 (Snapdragon variant with OLED) which report a > bit count of 0 but declares an 11-bit PWM capability range. > > Co-developed-by: Rui Miguel Silva > Signed-off-by: Rui Miguel Silva > Signed-off-by: Christopher Obbard > --- > Changes in v2: > - Split backlight brightness patch from T14s OLED enablement series. > - Use PWMGEN_CAP_MIN rather than MAX (Dmitry). > - Rework commit message to reference eDP spec. > - Rebase on drm-misc-next. > - Link to v1: https://lore.kernel.org/all/20250325-wip-obbardc-qcom-t14s-oled-panel-v2-4-e9bc7c9d30cc@linaro.org/ > --- > drivers/gpu/drm/display/drm_dp_helper.c | 50 ++++++++++++++++++++++----------- > 1 file changed, 33 insertions(+), 17 deletions(-) > > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c > index dbce1c3f49691fc687fee2404b723c73d533f23d..0b843d5b634f89f144b62b30311834d118b79ba9 100644 > --- a/drivers/gpu/drm/display/drm_dp_helper.c > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > @@ -4083,7 +4083,7 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > { > int fxp, fxp_min, fxp_max, fxp_actual, f = 1; > int ret; > - u8 pn, pn_min, pn_max; > + u8 pn, pn_min, pn_max, bl_caps; > > if (!bl->aux_set) > return 0; > @@ -4094,8 +4094,39 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > aux->name, ret); > return -ENODEV; > } > - > pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > + > + ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > + if (ret != 1) { > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > + aux->name, ret); > + return 0; > + } > + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > + > + ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > + if (ret != 1) { > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > + aux->name, ret); > + return 0; > + } > + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > + > + ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_ADJUSTMENT_CAP, &bl_caps); > + if (ret != 1) { > + bl_caps = 0; > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read backlight adjustment cap: %d\n", > + aux->name, ret); > + } > + > + /* > + * Some eDP panels report brightness byte count support, but the byte count > + * reading is 0 (e.g. Samsung ATNA40YK20) so use pn_min instead. > + */ > + if (!pn && (bl_caps & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT) > + && pn_min) > + pn = pn_min; I wonder, what stops you from implementing this part according to the standard, rather than adding a hack for 0 value. > + > bl->max = (1 << pn) - 1; > if (!driver_pwm_freq_hz) > return 0; -- With best wishes Dmitry