linux-kernel - RE: [PATCH v5 9/9] cxl/pci: Register for and process CPER events

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Date: Wed, 3 Jan 2024 14:08:02 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Ira Weiny <ira.weiny@...el.com>, Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, Shiju Jose <shiju.jose@...wei.com>
CC: Yazen Ghannam <yazen.ghannam@....com>, Davidlohr Bueso
	<dave@...olabs.net>, Dave Jiang <dave.jiang@...el.com>, Alison Schofield
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, "Ard
 Biesheuvel" <ardb@...nel.org>, <linux-efi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>, Ira Weiny
	<ira.weiny@...el.com>
Subject: RE: [PATCH v5 9/9] cxl/pci: Register for and process CPER events

Ira Weiny wrote:
> If the firmware has configured CXL event support to be firmware first
> the OS can process those events through CPER records.  The CXL layer has
> unique DPA to HPA knowledge and standard event trace parsing in place.
> 
> CPER records contain Bus, Device, Function information which can be used
> to identify the PCI device which is sending the event.
> 
> Change the PCI driver registration to include registration of a CXL
> CPER callback to process events through the trace subsystem.
> 
> Use new scoped based management to simplify the handling of the PCI
> device object.
> 
> NOTE this patch depends on Dan's addition of a device guard[1].

Now that you added guard(pci_dev) earlier in the series you can just use
that here rather than guard(device).

[..]
> +#define CXL_EVENT_HDR_FLAGS_REC_SEVERITY GENMASK(1, 0)
> +static void cxl_cper_event_call(enum cxl_event_type ev_type,
> +				struct cxl_cper_event_rec *rec)
> +{
> +	struct cper_cxl_event_devid *device_id = &rec->hdr.device_id;
> +	struct pci_dev *pdev __free(pci_dev_put) = NULL;
> +	enum cxl_event_log_type log_type;
> +	struct cxl_dev_state *cxlds;
> +	unsigned int devfn;
> +	u32 hdr_flags;
> +
> +	devfn = PCI_DEVFN(device_id->device_num, device_id->func_num);
> +	pdev = pci_get_domain_bus_and_slot(device_id->segment_num,
> +					   device_id->bus_num, devfn);
> +	if (!pdev)
> +		return;
> +
> +	guard(device)(&pdev->dev);

Per above:
	guard(pci_dev)(pdev);

> +	if (pdev->driver != &cxl_pci_driver)
> +		return;
> +
> +	cxlds = pci_get_drvdata(pdev);
> +	if (!cxlds)
> +		return;
> +
> +	/* Fabricate a log type */
> +	hdr_flags = get_unaligned_le24(rec->event.generic.hdr.flags);
> +	log_type = FIELD_GET(CXL_EVENT_HDR_FLAGS_REC_SEVERITY, hdr_flags);
> +
> +	cxl_event_trace_record(cxlds->cxlmd, log_type, ev_type,
> +			       &uuid_null, &rec->event);
> +}
> +
> +static int __init cxl_pci_driver_init(void)
> +{
> +	int rc;
> +
> +	rc = pci_register_driver(&cxl_pci_driver);
> +	if (rc)
> +		return rc;
> +
> +	rc = cxl_cper_register_callback(cxl_cper_event_call);
> +	if (rc)
> +		pci_unregister_driver(&cxl_pci_driver);

I think this order should be flipped. That way any errors that might
arrive due to activity caused by probing have a chance to be serviced.
Any that fire while initial probing is happening will pause in
cxl_cper_event_call() and wait for probing to complete. Of course if
probing fails, all is lost, but I think there is some incremental
benefit to trying to catch those early records for things that are not
probing fatal.