linux-kernel - Re: [PATCH] cxl: Add generic MSI/MSI-X interrupt support

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Date:   Wed, 12 Oct 2022 15:57:48 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Davidlohr Bueso <dave@...olabs.net>, dan.j.williams@...el.com
Cc:     ira.weiny@...el.com, Jonathan.Cameron@...wei.com,
        alison.schofield@...el.com, vishal.l.verma@...el.com,
        bwidawsk@...nel.org, a.manzanares@...sung.com,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org
Subject: Re: [PATCH] cxl: Add generic MSI/MSI-X interrupt support


On 10/12/2022 11:04 AM, Davidlohr Bueso wrote:
> Introduce a generic irq table for CXL components/features that can have
> standard irq support - DOE requires dynamic vector sizing and is not
> considered here.
>
> Create an infrastructure to query the max vectors required for the CXL
> device.
>
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>

LGTM. Although it would be nice to see the other half of the picture. 
i.e. having the mailbox consuming the vector via request_irq() as an 
example.

Reviewed-by: Dave Jiang <dave.jiang@...el.com>


> ---
>   drivers/cxl/pci.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 63 insertions(+)
>
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index faeb5d9d7a7a..467f2d568e3e 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -428,6 +428,66 @@ static void devm_cxl_pci_create_doe(struct cxl_dev_state *cxlds)
>   	}
>   }
>   
> +/**
> + * 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.  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[] = {
> +	{ "isolation", NULL },
> +	{ "pmu_overflow", NULL },
> +	{ "mailbox", NULL },
> +	{ "event", NULL },
> +};
> +
> +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++;
> +	rc = pci_alloc_irq_vectors(pdev, vectors, vectors,
> +				   PCI_IRQ_MSIX | PCI_IRQ_MSI);
> +	if (rc < 0)
> +		return rc;
> +
> +	if (rc != vectors) {
> +		dev_err(dev, "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 int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>   {
>   	struct cxl_register_map map;
> @@ -498,6 +558,9 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>   	if (IS_ERR(cxlmd))
>   		return PTR_ERR(cxlmd);
>   
> +	/* TODO: When there are users, this return value must be checked */
> +	cxl_pci_alloc_irq_vectors(cxlds);
> +
>   	if (resource_size(&cxlds->pmem_res) && IS_ENABLED(CONFIG_CXL_PMEM))
>   		rc = devm_cxl_add_nvdimm(&pdev->dev, cxlmd);
>