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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Oct 2025 00:44:51.7553 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 201aa90b-7820-40da-44bd-08de053ab9f3 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CH1PEPF0000A348.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB6061 On Wed, Sep 24, 2025 at 10:54:37AM -0700, Jacob Pan wrote: > While polling for n spaces in the cmdq, the current code instead checks > if the queue is full. If the queue is almost full but not enough space > ( polling has exceeded timeout limit. This does sound like an issue that is missing a warning print. > This patch polls for the availability of exact space instead of full and > emit timeout warning accordingly. And the solution sounds plausible as well. > @@ -806,10 +769,28 @@ int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu, > do { > u64 old; > > + queue_poll_init(smmu, &qp); > while (!queue_has_space(&llq, n + sync)) { > local_irq_restore(flags); > - if (arm_smmu_cmdq_poll_until_not_full(smmu, cmdq, &llq)) > - dev_err_ratelimited(smmu->dev, "CMDQ timeout\n"); > + /* > + * Try to update our copy of cons by grabbing exclusive cmdq access. If > + * that fails, spin until somebody else updates it for us. > + */ > + if (arm_smmu_cmdq_exclusive_trylock_irqsave(cmdq, flags)) { > + WRITE_ONCE(cmdq->q.llq.cons, readl_relaxed(cmdq->q.cons_reg)); > + arm_smmu_cmdq_exclusive_unlock_irqrestore(cmdq, flags); > + llq.val = READ_ONCE(cmdq->q.llq.val); > + local_irq_save(flags); > + continue; > + } > + > + ret = queue_poll(&qp); > + if (ret == -ETIMEDOUT) { > + dev_err_ratelimited(smmu->dev, "CPU %d CMDQ Timeout, C: %08x, CW:%x P: 0x%08x PW: %x cmdq.lock 0x%x\n", > + smp_processor_id(), Q_IDX(&llq, llq.cons), Q_WRP(&llq, llq.cons), Q_IDX(&llq, llq.prod), Q_WRP(&llq, llq.prod), atomic_read(&cmdq->lock)); > + queue_poll_init(smmu, &qp); > + } > + llq.val = READ_ONCE(cmdq->q.llq.val); > local_irq_save(flags); But, couldn't we write a new arm_smmu_cmdq_poll_until_enough_space() simply replacing arm_smmu_cmdq_exclusive_unlock_irqrestore()? This whole unwrapped piece is really not easy to read :( Also, the new error message has too much debugging info, which could be trimmed away, IMHO. Though kernel coding now does allow a higher limit per line, that 200-ish-character line is a bit overdone :-/ Nicolin