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Wed, 08 Jul 2026 23:28:34 -0700 (PDT) X-Received: by 2002:a05:6a00:cd6:b0:848:30c3:45d6 with SMTP id d2e1a72fcca58-84842ef886amr5946271b3a.14.1783578513823; Wed, 08 Jul 2026 23:28:33 -0700 (PDT) Received: from [192.168.31.103] ([152.58.31.181]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-847f6b9a832sm8089294b3a.18.2026.07.08.23.28.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Jul 2026 23:28:33 -0700 (PDT) Message-ID: <6b53fa97-0fae-4ba2-a774-ae8df2c2ad4e@oss.qualcomm.com> Date: Thu, 9 Jul 2026 11:58:27 +0530 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] i2c: qcom-geni: Add dynamic transfer timeout based on transfer length and frequency To: Konrad Dybcio , mukesh.savaliya@oss.qualcomm.com, viken.dadhaniya@oss.qualcomm.com, andi.shyti@kernel.org, sumit.semwal@linaro.org, christian.koenig@amd.com Cc: linux-i2c@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, naresh.maramaina@oss.qualcomm.com References: <20260705135739.4038826-1-aniket.randive@oss.qualcomm.com> <4f865aaf-a400-4dc6-acaa-80dc22a36af7@oss.qualcomm.com> Content-Language: en-US From: Aniket RANDIVE In-Reply-To: <4f865aaf-a400-4dc6-acaa-80dc22a36af7@oss.qualcomm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-GUID: Gri31t7dSGa7OTjkPsIRk0quV_izchk7 X-Proofpoint-ORIG-GUID: Gri31t7dSGa7OTjkPsIRk0quV_izchk7 X-Authority-Analysis: v=2.4 cv=GIg41ONK c=1 sm=1 tr=0 ts=6a4f3f93 cx=c_pps a=rEQLjTOiSrHUhVqRoksmgQ==:117 a=9AXozQ6IwN0d4JI31gUtBA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=Um2Pa8k9VHT-vaBCBUpS:22 a=5GfgTEDUgWdp11RPFvgA:9 a=QEXdDO2ut3YA:10 a=2VI0MkxyNR6bbpdq8BZq:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA5MDA1OSBTYWx0ZWRfX++TVpFLyT/60 O+wDZ01i7xWI54svuULnJQiZCw5icK+OgoJrIgT6AFW0/lf0MqxCwWnai9pfq73E8pRN3TA5jH+ ckNRzLy7+kPtQH1KGwVGgdSF1c39k5cSrRPvQpiuZ7SlET5zlFbb8JwHZUBUpTcpuwest5x8n/B Dn/bMbn2Qr2JcHznydNmBULcgTBKnkFg9sxxtnyndmF+WBRxwC/e7tMiBwbHK/GG+nh6NjIxnXi J1FH/Zp4+J64P6uM4u+8oLiLqR68fHsMWWmYF1KCMS1wdgokTN4hU299ZzBli4TAlIJY1LoBFFU /US7KNK8uicLY9/BvAVm60OBNYvOI7bKe/9H2/KeUy1i0U854EyBZC2hK36vD90DH/6b3uTzLGA TPbt9nJ0H5cSLrhcSomNa9h9FhnZ7tk4upK9DnDkNnTCVbjiqbCkv88MVeXpqGja+ZjC69Lj2sZ xKKco3m/sTrkcn0dvPQ== X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA5MDA1OSBTYWx0ZWRfX264Ni+YgL0h1 yL36eY8cXaRiSC3/PtzUTPSl86eBR+CklocTLf0hIv5FEafvo3F0kWGnChZwzPkhah0MCrW7p9n OgFZCbBYpGaHKKr1MOq0Km7wJpxXzUg= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-09_01,2026-07-08_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 clxscore=1015 suspectscore=0 adultscore=0 priorityscore=1501 spamscore=0 malwarescore=0 bulkscore=0 impostorscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607090059 Thanks Konrad for the review. Sorry, I missed your comments on the v2 patch and ended up posting v3. I'm happy to post a v4 incorporating your feedback once the discussion concludes. On 7/6/2026 5:11 PM, Konrad Dybcio wrote: > On 7/5/26 3:57 PM, Aniket Randive wrote: >> The driver uses a static XFER_TIMEOUT of HZ (1 second) for all transfers >> regardless of message length or bus frequency, causing unnecessary >> delays on error paths. >> >> Compute the timeout dynamically from message length and bus frequency >> with a 10x safety margin over the theoretical wire time and a 300ms >> floor. For GPI multi-descriptor transfers, use the maximum message >> length across all queued messages as the per-completion timeout. > > What's the reason for a 0.3 s floor? The floor accounts for I2C clock stretching. The spec allows slaves to hold SCL low indefinitely during internal processing. A dynamically computed xfer time alone gives no time for that. 300ms value covers worst-case stretching while still detecting real hangs 3x faster than the old 1s static timeout. Thanks, Aniket > > Why a 10x safety margin specifically? > > [...] The multiplier covers the gap between theoretical xfer time and actual completion time (DMA descriptor setup, interrupt latency, and scheduling jitter on a loaded system) Without it, short transfers would have almost no extra time before a spurious timeout. Thanks, Aniket > >> +static unsigned long geni_i2c_xfer_timeout(struct geni_i2c_dev *gi2c, size_t len) >> +{ >> + size_t bit_cnt = len * 9; >> + size_t bit_usec = (bit_cnt * USEC_PER_SEC) / gi2c->clk_freq_out; > > mult_frac() > > Konrad Good catch. I'll switch the calculation to mult_frac() as suggested in the next v4 patch. Thanks, Aniket