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[78.88.45.245]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-670703f5b31sm621074a12.11.2026.04.10.07.29.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Apr 2026 07:29:46 -0700 (PDT) Message-ID: <7d65539f-ece6-4e7c-a13e-6b12920346fa@oss.qualcomm.com> Date: Fri, 10 Apr 2026 16:29:43 +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] thunderbolt: debugfs: Don't stop reading SB registers if just one fails To: Mika Westerberg Cc: Konrad Dybcio , Andreas Noever , Mika Westerberg , Yehezkel Bernat , usb4-upstream@oss.qualcomm.com, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260409-topic-tbt_sb_debugfs-v1-1-131540e0cc2b@oss.qualcomm.com> <20260409120457.GH3552@black.igk.intel.com> <75c962d1-7ade-483b-bbc9-a6c6140fc0e9@oss.qualcomm.com> <20260409143203.GI3552@black.igk.intel.com> Content-Language: en-US From: Konrad Dybcio In-Reply-To: <20260409143203.GI3552@black.igk.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDEwMDEzNSBTYWx0ZWRfX/SNnbtd14smz bcjgQ5e24KvQF1NXM6EL3RCW5Qw1mmKwJO24qEz2fVr5x5XtZmWQ35420Tyc1dNUIAoe0UrahNy 1SdPIR+TCAFK8GiGdikyUmD8vY843Nqt89Yfsuk8RmhUibQ/IKsEhb5ra3RvvhZe0guTcJlhls7 LZ+jNEBkxGr63SrCtdQrQTuIME4vA/ve0g82Vqs3+X5z8Qy0aki+Vnscf2QwTGGgXkcZLLxMYjf i8C5QvMOy/CDRCLc5raK4ghNlKEV9lt+ZNr/iuIaoMA1wm/QIB0iPPPNLvFBnh+oFX5IA8guoF9 7Ok1daGgluVt6KQhdnmVyq8/iNrjJyz/EbkMJiV6AtnbeinXZYDHWEymdIeoPaWsHtiHthvNhsQ 6pqY8EbtyFoZLC57ltNfzEvMZ//ynAShl/G4zuL4VABNcsFXiDaHLtJTa+guJLSl1fG8r3jr93g B7o99IVadh9JhWkst/A== X-Proofpoint-GUID: qgiUnlBR-afq65HdjxY89Gvjv2u272Of X-Authority-Analysis: v=2.4 cv=d6fFDxjE c=1 sm=1 tr=0 ts=69d9095d cx=c_pps a=HLyN3IcIa5EE8TELMZ618Q==:117 a=FpWmc02/iXfjRdCD7H54yg==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=eoimf2acIAo5FJnRuUoq:22 a=t5gs6XZINShnl3d-aGYA:9 a=QEXdDO2ut3YA:10 a=bTQJ7kPSJx9SKPbeHEYW:22 X-Proofpoint-ORIG-GUID: qgiUnlBR-afq65HdjxY89Gvjv2u272Of 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=2026-04-10_04,2026-04-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 phishscore=0 lowpriorityscore=0 malwarescore=0 clxscore=1015 impostorscore=0 adultscore=0 bulkscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604100135 On 4/9/26 4:32 PM, Mika Westerberg wrote: > On Thu, Apr 09, 2026 at 02:59:22PM +0200, Konrad Dybcio wrote: >> On 4/9/26 2:04 PM, Mika Westerberg wrote: [...] >>> I assume you have tested this on a hardware that supports this too, right? >> >> Hardware that exposes that register this does not exercise the altered >> code path. > > Well it may happen now that previously we got -EIO from some other register > and we stopped there, now this changes and we actually continue reading so > this definitely should be tested. The only register before USB4_SB_GEN4_TXFFE that isn't in-spec for both retimers in v1.0 and v2.0 is USB4_SB_LRD_TUNING (0x07). The PS8830 interestingly reports all zeroes (not a bounce). The registers following USB4_SB_GEN4_TXFFE in the array are USB4_SB_VERSION and USB4_SB_DATA. The former is not accessed anywhere else in the code, at first glance. The latter is, during NVM r/w and in margining ops, which have definitely been in use for a long time. Plus both of them are the v1.0 spec. The USB4_SB_GEN4_TXFFE specifically isn't (the retimer supplement pdf lists it as Rsvd, the main spec pdf omits it in the SB register table), as it wasn't previously useful (since Gen4 came about in v2.0). I don't think there's an easy way to limit the reading of this register since the bit indicating Gen4 capability is in USB4_SB_LINK_CONF (0x0c), which is Rsvd on retimers regardless of the spec revision. A connected port could easily have higher/lower capabilities, too. So all in all, my understanding is that any bugs caused by this patch (which would have to be in the form of "reading a register causes a wrongful change in behavior") would really surface spec non-compliance from a retimer, which should be quirked out explicitly if that's the case. I only have hardware with various Parade retimers, none of which claim Gen4 support. Konrad