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[103.229.16.4]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29651cd2418sm50884275ad.109.2025.11.06.23.45.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Nov 2025 23:45:39 -0800 (PST) From: Zhongqiu Han To: jonathan.lemon@gmail.com, vadim.fedorenko@linux.dev, richardcochran@gmail.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, zhongqiu.han@oss.qualcomm.com Subject: [PATCH] ptp: ocp: Document sysfs output format for backward compatibility Date: Fri, 7 Nov 2025 15:45:33 +0800 Message-ID: <20251107074533.416048-1-zhongqiu.han@oss.qualcomm.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTA3MDA2MCBTYWx0ZWRfXwT4R4yUpgaFY UhATkbhsMU+D4kTw7A6FZVn2rxjBBcs/R2FGzQgLwbUddZZmkV+RnLQIPiDK5rbetFhDgi4yS8h jdSJZ2tYJ1WmW7qBZXvK96/+H52k+k6ekkqOzdUVe75kPLSVeTFm98MSunINFoG2YzXP0UogD7+ bSAEC1GP8zaZBN2/JTGdsl6nefByIXNzscRe4ohJ5wIHzRRkHnMXrIqyyZ0hhw7Qq4bUPAAxD5S YQYVbzCFZfXJn33EAeaNm2wPEwXDQDh0yVV7+kZkfBIpOBxTOXd1wgq7c2YsCZgr9vijrG5sm8i MERxYrQFEq8eAp+Wpza/UXSBOWpudya2EMSW8ctfD/COo5AvM4KtFIXkTra0tVWoOUunjfODDS2 fgRtFDhMlItNZNXVmxgQUV8NMXHAHA== X-Proofpoint-ORIG-GUID: jULUF9MXihyO8yaQgJK94oMF9StBX3tz X-Authority-Analysis: v=2.4 cv=A+hh/qWG c=1 sm=1 tr=0 ts=690da3a5 cx=c_pps a=MTSHoo12Qbhz2p7MsH1ifg==:117 a=nuhDOHQX5FNHPW3J6Bj6AA==:17 a=6UeiqGixMTsA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=EUspDBNiAAAA:8 a=P3xlrWuPvaME_hMzoIMA:9 a=GvdueXVYPmCkWapjIL-Q:22 X-Proofpoint-GUID: jULUF9MXihyO8yaQgJK94oMF9StBX3tz X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-07_01,2025-11-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 lowpriorityscore=0 suspectscore=0 spamscore=0 bulkscore=0 malwarescore=0 impostorscore=0 phishscore=0 priorityscore=1501 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2510240001 definitions=main-2511070060 Content-Type: text/plain; charset="utf-8" Add a comment to ptp_ocp_tty_show() explaining that the sysfs output intentionally does not include a trailing newline. This is required for backward compatibility with existing userspace software that reads the sysfs attribute and uses the value directly as a device path. A previous attempt to add a newline to align with common kernel conventions broke userspace applications that were opening device paths like "/dev/ttyS4\n" instead of "/dev/ttyS4", resulting in ENOENT errors. This comment prevents future attempts to "fix" this behavior, which would break existing userspace applications. Link: https://lore.kernel.org/netdev/20251030124519.1828058-1-zhongqiu.han@= oss.qualcomm.com/ Link: https://lore.kernel.org/netdev/aef3b850-5f38-4c28-a018-3b0006dc2f08@l= inux.dev/ Suggested-by: Jakub Kicinski Signed-off-by: Zhongqiu Han Reviewed-by: Vadim Fedorenko --- drivers/ptp/ptp_ocp.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c index a5c363252986..eeebe4d149f7 100644 --- a/drivers/ptp/ptp_ocp.c +++ b/drivers/ptp/ptp_ocp.c @@ -3430,6 +3430,12 @@ ptp_ocp_tty_show(struct device *dev, struct device_a= ttribute *attr, char *buf) struct dev_ext_attribute *ea =3D to_ext_attr(attr); struct ptp_ocp *bp =3D dev_get_drvdata(dev); =20 + /* + * NOTE: This output does not include a trailing newline for backward + * compatibility. Existing userspace software uses this value directly + * as a device path (e.g., "/dev/ttyS4"), and adding a newline would + * break those applications. Do not add a newline to this output. + */ return sysfs_emit(buf, "ttyS%d", bp->port[(uintptr_t)ea->var].line); } =20 --=20 2.43.0