Message-ID: <e42daada-2471-6379-f06b-77d2e9044132@intel.com>
Date:   Thu, 1 Sep 2022 11:10:22 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Ira Weiny <ira.weiny@...el.com>
Cc:     Davidlohr Bueso <dave@...olabs.net>,
        Dan Williams <dan.j.williams@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>, a.manzanares@...sung.com,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org
Subject: Re: [RFC PATCH 0/9] CXL: Read and clear event logs


On 8/24/2022 3:07 AM, Jonathan Cameron wrote:
> On Mon, 22 Aug 2022 15:53:54 -0700
> Ira Weiny <ira.weiny@...el.com> wrote:
>
>> On Mon, Aug 22, 2022 at 09:18:02AM -0700, Davidlohr Bueso wrote:
>>> On Fri, 12 Aug 2022, ira.weiny@...el.com wrote:
>>>    
>>>> From: Ira Weiny <ira.weiny@...el.com>
>>>>
>>>> Event records inform the OS of various device events.  Events are not needed
>>>> for any kernel operation but various user level software will want to track
>>>> events.
>>>>
>>>> Add event reporting through the trace event mechanism.  On driver load read and
>>>> clear all device events.
>>>>
>>>> Normally interrupts will trigger new events to be reported as they occur.
>>>> Because the interrupt code is still being worked on this series provides a
>>>> cxl-test mechanism to create a series of events and trigger the reporting of
>>>> those events.
>>> Where is this irq code being worked on? I've asked about this for async mbox
>>> commands, and Jonathan has also posted some code for the PMU implementation.
>> I'm still trying to work out how to share irq's between PCI and CXL.  Mainly
>> for DOE.
>>
>> I thought that we could skip IRQ support for DOE completely and this would
>> support your proposal below.  But I just found that:
>>
>> "A device may interrupt the host when CDAT content changes using the MSI
>> associated with this DOE Capability instance."
> As of today that doesn't work because there is no status flag anywhere to let
> you know that was the interrupt source.
>
> It's been raised in appropriate places, but I can't say anymore on that
> until stuff is published.
>
> Hence I'd not worry about that corner for now.
>
>> So I guess it needs to be supported at some point.
>>
>>> Could we not just start with an initial MSI/MSI-X support? Then gradually
>>> interested users can be added? So each "feature" would need to do implement
>>> it's "get message number" and to install the isr just do the standard:
>>>
>>>       irq = pci_irq_vector(pdev, num);
>>>       irq_name = devm_kasprintf(dev, GFP_KERNEL, "%s_%s\n", dev_name(dev),
>>> 			       cxl_irq_cap_table[feature].name);
>>>       rc = devm_request_irq(dev, irq, isr_fn, IRQF_SHARED, irq_name, info);
>>>
>>> The only complexity I see for this is to know the number of vectors to request
>>> apriori, for which we'd have to get the larges value of all CXL features that
>>> can support interrupts. Something like the following?
>> Generally it seems ok but I have questions below.
>>
>>> One thing I have not
>>> considered in this is the DOE stuff.
>> I think this is the harder thing to support because of needing to allow both
>> the PCI layer and the CXL layer to create irqs.  Potentially at different
>> times.
> My reasoning on this is that IRQ creation has to be done by
> the PCI device driver.  That may result in some juggling and late starting
> or indeed restarting of DOE mailboxes once we can know the list of vectors.
> (e.g. query them by polling, then a later driver register can request enabling
> the DOE with an irq).
> Or it needs the ability to do dynamic increasing of the requested IRQ vectors.

tglx was working on dynamic MSIX a while back. not sure the state of 
that now

https://lore.kernel.org/lkml/87a6hof5sr.ffs@tglx/T/

DJ

>
>>> Thanks,
>>> Davidlohr
>>>
>>> ------
>>> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
>>> index 88e3a8e54b6a..b334d2f497c1 100644
>>> --- a/drivers/cxl/cxlmem.h
>>> +++ b/drivers/cxl/cxlmem.h
>>> @@ -245,6 +245,8 @@ struct cxl_dev_state {
>>> 	resource_size_t component_reg_phys;
>>> 	u64 serial;
>>>
>>> +	int irq_type; /* MSI-X, MSI */
>>> +
>>> 	struct xarray doe_mbs;
>>>
>>> 	int (*mbox_send)(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *cmd);
>>> diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
>>> index eec597dbe763..95f4b91f43b1 100644
>>> --- a/drivers/cxl/cxlpci.h
>>> +++ b/drivers/cxl/cxlpci.h
>>> @@ -53,15 +53,6 @@
>>>   #define	    CXL_DVSEC_REG_LOCATOR_BLOCK_ID_MASK			GENMASK(15, 8)
>>>   #define     CXL_DVSEC_REG_LOCATOR_BLOCK_OFF_LOW_MASK		GENMASK(31, 16)
>>>
>>> -/* Register Block Identifier (RBI) */
>>> -enum cxl_regloc_type {
>>> -	CXL_REGLOC_RBI_EMPTY = 0,
>>> -	CXL_REGLOC_RBI_COMPONENT,
>>> -	CXL_REGLOC_RBI_VIRT,
>>> -	CXL_REGLOC_RBI_MEMDEV,
>>> -	CXL_REGLOC_RBI_TYPES
>>> -};
>> Why move this?
>>
>>> -
>>>   static inline resource_size_t cxl_regmap_to_base(struct pci_dev *pdev,
>>> 						 struct cxl_register_map *map)
>>>   {
>>> @@ -75,4 +66,44 @@ int devm_cxl_port_enumerate_dports(struct cxl_port *port);
>>>   struct cxl_dev_state;
>>>   int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm);
>>>   void read_cdat_data(struct cxl_port *port);
>>> +
>>> +#define CXL_IRQ_CAPABILITY_TABLE				\
>>> +	C(ISOLATION, "isolation", NULL),			\
>>> +	C(PMU, "pmu_overflow", NULL), /* per pmu instance */	\
>>> +	C(MBOX, "mailbox", NULL), /* primary-only */		\
>>> +	C(EVENT, "event", NULL),
>> This is defining get_max_msgnum to NULL right?
>>
>>> +
>>> +#undef C
>>> +#define C(a, b, c) CXL_IRQ_CAPABILITY_##a
>>> +enum  { CXL_IRQ_CAPABILITY_TABLE };
>>> +#undef C
>>> +#define C(a, b, c) { b, c }
>>> +/**
>>> + * struct cxl_irq_cap - CXL feature that is capable of receiving MSI/MSI-X irqs.
>>> + *
>>> + * @name: Name of the device generating this interrupt.
>>> + * @get_max_msgnum: Get the feature's largest interrupt message number. In cases
>>> + *                  where there is only one instance it also indicates which
>>> + *                  MSI/MSI-X vector is used for the interrupt message generated
>>> + *                  in association with the feature. If the feature does not
>>> + *                  have the Interrupt Supported bit set, then return -1.
>>> + */
>>> +struct cxl_irq_cap {
>>> +	const char *name;
>>> +	int (*get_max_msgnum)(struct cxl_dev_state *cxlds);
>>> +};
>>> +
>>> +static const
>>> +struct cxl_irq_cap cxl_irq_cap_table[] = { CXL_IRQ_CAPABILITY_TABLE };
>>> +#undef C
>> Why all this macro magic?
> Agreed. I'm rarely persuaded it's a good idea to do this sort of trickery
> and it definitely isn't worth the readabilty problems unless there a
> large number of users.
>
>>> +
>>> +/* Register Block Identifier (RBI) */
>>> +enum cxl_regloc_type {
>>> +	CXL_REGLOC_RBI_EMPTY = 0,
>>> +	CXL_REGLOC_RBI_COMPONENT,
>>> +	CXL_REGLOC_RBI_VIRT,
>>> +	CXL_REGLOC_RBI_MEMDEV,
>>> +	CXL_REGLOC_RBI_TYPES
>>> +};
>>> +
>>>   #endif /* __CXL_PCI_H__ */
>>> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
>>> index faeb5d9d7a7a..c0fe78e0559b 100644
>>> --- a/drivers/cxl/pci.c
>>> +++ b/drivers/cxl/pci.c
>>> @@ -387,6 +387,52 @@ static int cxl_setup_regs(struct pci_dev *pdev, enum cxl_regloc_type type,
>>> 	return rc;
>>>   }
>>>
>>> +static void cxl_pci_free_irq_vectors(void *data)
>>> +{
>>> +	pci_free_irq_vectors(data);
>>> +}
>>> +
>>> +static int cxl_pci_alloc_irq_vectors(struct cxl_dev_state *cxlds)
>>> +{
>>> +	struct device *dev = cxlds->dev;
>>> +	struct pci_dev *pdev = to_pci_dev(dev);
>>> +	int rc, i, vectors = -1;
>>> +
>>> +	for (i = 0; i < ARRAY_SIZE(cxl_irq_cap_table); i++) {
>>> +		int irq;
>>> +
>>> +		if (!cxl_irq_cap_table[i].get_max_msgnum)
>>> +			continue;
>>> +
>>> +		irq = cxl_irq_cap_table[i].get_max_msgnum(cxlds);
>>> +		vectors = max_t(int, irq, vectors);
>>> +	}
>>> +
>>> +	if (vectors == -1)
>>> +		return -EINVAL; /* no irq support whatsoever */
>>> +
>>> +	vectors++;
>> This is pretty much what earlier versions of the DOE code did with the
>> exception of only have 1 get_max_msgnum() calls defined (for DOE).  But there
>> was a lot of debate about how to share vectors with the PCI layer.  And
>> eventually we got rid of it.  I'm still trying to figure it out.  Sorry for
>> being slow.
> I'm not yet setting huge advantage in wrapping this up. For now a set of
> linear calls to establish the max irq vector is more readable.  Sure
> down the line moving to this may make sense.
>
>> Perhaps we do this for this series.  However, won't we have an issue if we want
>> to support switch events?
> We 'could' extend existing stuff in the portdrv code (which is ultimately
> where this general approach was copied from ;) but I suspect doing that
> for non generic PCI stuff is going to be controversial.
>
> That whole infrastructure in PCI may need a rewrite.
>
>> Ira
>>
>>> +	rc = pci_alloc_irq_vectors(pdev, vectors, vectors, PCI_IRQ_MSIX);
>>> +	if (rc < 0) {
>>> +		rc = pci_alloc_irq_vectors(pdev, vectors, vectors, PCI_IRQ_MSI);
>>> +		if (rc < 0)
>>> +			return rc;
>>> +
>>> +		cxlds->irq_type = PCI_IRQ_MSI;
>>> +	} else {
>>> +		cxlds->irq_type = PCI_IRQ_MSIX;
>>> +	}
>>> +
>>> +	if (rc != vectors) {
>>> +		pci_err(pdev, "Not enough interrupts; use polling where supported\n");
>>> +		/* Some got allocated; clean them up */
>>> +		cxl_pci_free_irq_vectors(pdev);
>>> +		return -ENOSPC;
>>> +	}
>>> +
>>> +	return devm_add_action_or_reset(dev, cxl_pci_free_irq_vectors, pdev);
>>> +}
>>> +
>>>   static void cxl_pci_destroy_doe(void *mbs)
>>>   {
>>> 	xa_destroy(mbs);
>>> @@ -476,6 +522,9 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>>>
>>> 	cxlds->component_reg_phys = cxl_regmap_to_base(pdev, &map);
>>>
>>> +	if (cxl_pci_alloc_irq_vectors(cxlds))
>>> +		cxlds->irq_type = 0;
>>> +
>>> 	devm_cxl_pci_create_doe(cxlds);
>>>
>>> 	rc = cxl_pci_setup_mailbox(cxlds);

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