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[78.88.45.245]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-670702eec4fsm2433859a12.6.2026.04.13.04.43.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Apr 2026 04:43:51 -0700 (PDT) Message-ID: Date: Mon, 13 Apr 2026 13:43:49 +0200 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC] thunderbolt: Skip reading Rsvd SB registers on older-gen hardware To: Mika Westerberg , Konrad Dybcio Cc: Andreas Noever , Mika Westerberg , Yehezkel Bernat , Greg Kroah-Hartman , Gil Fine , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260413-topic-usb4_limit_sb_reads-v1-1-778a6eb37f7b@oss.qualcomm.com> <20260413114015.GO3552@black.igk.intel.com> Content-Language: en-US From: Konrad Dybcio In-Reply-To: <20260413114015.GO3552@black.igk.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Authority-Analysis: v=2.4 cv=PuijqQM3 c=1 sm=1 tr=0 ts=69dcd6fa cx=c_pps a=EVbN6Ke/fEF3bsl7X48z0g==:117 a=FpWmc02/iXfjRdCD7H54yg==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yOCtJkima9RkubShWh1s:22 a=EUspDBNiAAAA:8 a=rX3LUgZ8ABPdRQFCJgUA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=a_PwQJl-kcHnX1M80qC6:22 X-Proofpoint-ORIG-GUID: 0_Rc9_-IijVbkgfttNpTZXbNnnWuopMU X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDEzMDExNSBTYWx0ZWRfX/XpnadNMFLKm 7lobtlmzp3HWVIMCFRiqjbc5i7VXD8ajom0cgmAFauAvbEW3UpT/Aadz8my/wTEvMeBt5ySaQWW VfIeN3CPoqcsqbh2qzO2ACmq6QGISgzdnRAsJgWfYgzltmGvq0EGst9mjlc4YqufM6+ebE/Wc3J xwcb3EBQJOJsSMKjob9XTkrENR1rapwYZAfkMW6reM4e24yMrS71SsLA4c2vH90+U7xdxuRbvoO AT6QMhjrIq+vEzRzJ9KW/I+azVXVWRMC+jsYhcS1ooZGSnl6hfMVsMvD42NThmsj+SJeGpVS8TU 1OrYxItboL9Gv6gcvvWnK76k6nErAY2UXUdGpv7sIqZpyXqIHSTeRWssnKtVcaRa3aeQ94ZS2gX +HkWAN1mgWl/NRmLk0itLZTiyZtmj0ZOUauZCFRKAmeskZErwdUeLlbUko38cPj1nB0gryGRX4L 2EPERB5TcipQD979CNA== X-Proofpoint-GUID: 0_Rc9_-IijVbkgfttNpTZXbNnnWuopMU 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=2026-04-13_03,2026-04-13_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 suspectscore=0 spamscore=0 phishscore=0 malwarescore=0 clxscore=1015 impostorscore=0 adultscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604130115 On 4/13/26 1:40 PM, Mika Westerberg wrote: > On Mon, Apr 13, 2026 at 12:54:41PM +0200, Konrad Dybcio wrote: >> From: Konrad Dybcio >> >> The Linux TBT subsystem supports hardware aligned with the latest >> USB4 v2.0 specification. In some places though, it assumes registers >> only defined in that specification version (previously marked as >> Reserved) are always accessible. >> >> Every version of the spec states: >> >> """ >> Unless specified otherwise, the Connection Manager shall not write a >> register with a value that is marked as “Rsvd”. Writing a register with >> a value that is marked as “Rsvd” results in undefined behavior. >> """ >> >> The effective list of SB registers that need this guarding currently >> exclusively contains ones that aren't used outside the debugfs dump >> logic, so just add the required checks there. >> >> Fixes: 54e418106c76 ("thunderbolt: Add debugfs interface") >> Signed-off-by: Konrad Dybcio >> --- >> drivers/thunderbolt/debugfs.c | 20 ++++++++++++-------- >> drivers/thunderbolt/retimer.c | 11 ++++++++++- >> drivers/thunderbolt/sb_regs.h | 11 ++++++----- >> drivers/thunderbolt/tb.h | 2 ++ >> 4 files changed, 30 insertions(+), 14 deletions(-) > > This is alternative for the v2 patch you sent earlier, right? I prefer that > one over this. I think they're complementary. This patch ensures compliance with the quoted part of the spec, while the other one improves the UX and aids debugging. Konrad