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Wed, 06 May 2026 01:09:03 -0700 (PDT) Received: from brgl-qcom.home ([2a01:cb1d:dc:7e00:1cd7:fa68:b1e1:a93e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e530c1d07sm10955095e9.9.2026.05.06.01.09.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 May 2026 01:09:02 -0700 (PDT) From: Bartosz Golaszewski To: Linus Walleij , Bartosz Golaszewski , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Maxime Ripard , Chanhong Jung Cc: Bartosz Golaszewski , linux-gpio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/2] gpio: 74x164: seed the chain from DT at probe time Date: Wed, 6 May 2026 10:09:00 +0200 Message-ID: <177805490864.4124.505982607018854833.b4-ty@oss.qualcomm.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260429035134.1023330-1-happycpu@gmail.com> References: <20260429035134.1023330-1-happycpu@gmail.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Proofpoint-GUID: xOjlPlf_UfqHqCScjW9sPMpEKHbseU4j X-Proofpoint-ORIG-GUID: xOjlPlf_UfqHqCScjW9sPMpEKHbseU4j X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA2MDA3OCBTYWx0ZWRfX1y/wR9ZlFkHc WxnI6RV/lmlai2ZUQwxyrtYlbNo/mn0k1Z7aLpbD1brraO9ThLs4WcMS+pDKhdD+YKHSF+lEA45 1rHg2fCVJgOFe6epJ6baIkvtPoHMo7gVAjuQ9OqNQ++cRsO7/UXfFOBXC9c+pc4NU+s3xoHMfXl bvvalpqVD/4VpswSkedTfK04LD/q+da0aQzoL6BUczT5k6aVM555eyKjvBonHhkZ+Ng/+V3qvio qai3lIK3Dp3osRdg80L7MRB8TesK/RKhZ0D4zWn53RPLMgc3bI7bma6zIFs2WM5MXFMoxrn8N6L Cipz+sNKf61KduHLtHqEXpTmqjC/EqUAc1h+k9JiVDXdJkCb4765mRX6pI3OeeEFxD1dJRj7Le+ ALGdRaOkVc9VE1QbI99N3+eXRMVLiOwPciIHx5ZgA9tY9DBTXp46hKT9X/zgfA0DrM7VbbK8vM7 VumgKeso4C0zlCIvPCA== X-Authority-Analysis: v=2.4 cv=A8xc+aWG c=1 sm=1 tr=0 ts=69faf720 cx=c_pps a=WeENfcodrlLV9YRTxbY/uA==:117 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=gowsoOTTUOVcmtlkKump:22 a=VwQbUJbxAAAA:8 a=EUspDBNiAAAA:8 a=h0xZeIPYvt9JjOhX5-wA:9 a=QEXdDO2ut3YA:10 a=kacYvNCVWA4VmyqE58fU:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-05_03,2026-04-30_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 phishscore=0 bulkscore=0 clxscore=1015 lowpriorityscore=0 malwarescore=0 adultscore=0 impostorscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605060078 On Wed, 29 Apr 2026 12:51:32 +0900, Chanhong Jung wrote: > This v2 reuses the existing lines-initial-states bitmask, as suggested > by Linus Walleij, instead of inventing a new property. That sidesteps > both the v1 review concerns at once: there is no vendor-specific > property to argue about, and the bit-N-equals-line-N convention is > already documented for nxp,pcf8575. > > Background (carried over from v1): > The 74HC595 / 74LVC594 family is push-pull output only. There is no > read-back path, no defined power-on state for the parallel outputs, and > __gen_74x164_write_config() always shifts the full chain on every > transaction. The driver therefore publishes whatever sits in > chip->buffer on the very first ->set() call, and today that buffer is > fresh from kzalloc(), so all outputs come up low. On boards with active- > low indicators or other signals whose initial level matters, the 0x00 > publish glitches the chain before user space (or gpio-leds default-state > walking) gets a chance to run. > > [...] Reluctantly applied. [1/2] dt-bindings: gpio: fairchild,74hc595: add lines-initial-states property https://git.kernel.org/brgl/c/d6e1a94888f5a4306c9998944a0f29f7bcd49411 [2/2] gpio: 74x164: support lines-initial-states for boot-time output state https://git.kernel.org/brgl/c/cb77f8933467d08c8896674cd39ca98550a70fd6 Best regards, -- Bartosz Golaszewski