linux-kernel - Re: [PATCH 1/2] cxl/pci: Add generic MSI-X/MSI irq support

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Date:   Tue, 18 Oct 2022 10:36:19 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Davidlohr Bueso <dave@...olabs.net>
CC:     <dan.j.williams@...el.com>, <ira.weiny@...el.com>,
        <dave.jiang@...el.com>, <alison.schofield@...el.com>,
        <bwidawsk@...nel.org>, <vishal.l.verma@...el.com>,
        <a.manzanares@...sung.com>, <linux-cxl@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] cxl/pci: Add generic MSI-X/MSI irq support

On Mon, 17 Oct 2022 20:00:09 -0700
Davidlohr Bueso <dave@...olabs.net> 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. For now the table is empty.
> 
> Create an infrastructure to query the max vectors required for the CXL
> device. Upon successful allocation, users can plug in their respective isr
> at any point thereafter, which is supported by a new cxlds->has_irq flag,
> for example, if the irq setup is not done in the PCI driver, such as
> the case of the CXL-PMU.
> 
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>

A few nitpicks inline.

With the comment one tidied up (other one optional)
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

I'll rebase my cpmu code on top of this shortly.

Jonathan


> ---
>  drivers/cxl/cxlmem.h |  3 ++
>  drivers/cxl/pci.c    | 72 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 75 insertions(+)
> 
> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> index 88e3a8e54b6a..72b69b003302 100644
> --- a/drivers/cxl/cxlmem.h
> +++ b/drivers/cxl/cxlmem.h
> @@ -211,6 +211,7 @@ struct cxl_endpoint_dvsec_info {
>   * @info: Cached DVSEC information about the device.
>   * @serial: PCIe Device Serial Number
>   * @doe_mbs: PCI DOE mailbox array
> + * @has_irq: PCIe MSI-X/MSI support
>   * @mbox_send: @dev specific transport for transmitting mailbox commands
>   *
>   * See section 8.2.9.5.2 Capacity Configuration and Label Storage for
> @@ -247,6 +248,8 @@ struct cxl_dev_state {
>  
>  	struct xarray doe_mbs;
>  
> +	bool has_irq;
> +
>  	int (*mbox_send)(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *cmd);
>  };
>  
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index faeb5d9d7a7a..9c3e95ebaa26 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -428,6 +428,73 @@ static void devm_cxl_pci_create_doe(struct cxl_dev_state *cxlds)
>  	}
>  }
>  
> +/**
> + * struct cxl_irq_cap - CXL feature that is capable of receiving MSI-X/MSI irqs.
> + *
> + * @name: Name of the device/component 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[] = {
> +	NULL
> +};
> +
> +static void cxl_pci_free_irq_vectors(void *data)
> +{
> +	pci_free_irq_vectors(data);
> +}
> +
> +/*
> + * Attempt to allocate the largest amount of necessary vectors.
> + *
> + * Returns 0 upon a successful allocation of *all* vectors, or a

Technically not all vectors.  If we wanted to do that we could
just directly query that via pci_msix_vec_count() etc that gets
it from the MSIX capability. That's frowned upon because it's common
to stick lots of extra vectors on the end for stuff that linux never
cares about (debug etc, or optional features).

All vectors up to the maximum one the code uses would be more accurate.

> + * negative value otherwise.
> + */
> +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);
> +	}
> +
> +	/*
> +	 * Semantically lack of irq support is not an error, but we
> +	 * still fail to allocate, so return negative.
> +	 */
> +	if (vectors == -1)
> +		return -1;
> +
> +	vectors++;
> +	rc = pci_alloc_irq_vectors(pdev, vectors, vectors,
> +				   PCI_IRQ_MSIX | PCI_IRQ_MSI);
> +	if (rc < 0)
> +		return rc;
> +
> +	if (rc != vectors) {
> +		dev_dbg(dev, "Not enough interrupts; use polling instead.\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;
> @@ -494,6 +561,11 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	if (rc)
>  		return rc;
>  
> +	if (!cxl_pci_alloc_irq_vectors(cxlds)) {
> +		cxlds->has_irq = true;
> +	} else
> +		cxlds->has_irq = false;
> +
	cxlds->has_irq = !(cxl_pci_aloc_irq_vectors(cxlds) < 0);

maybe...

>  	cxlmd = devm_cxl_add_memdev(cxlds);
>  	if (IS_ERR(cxlmd))
>  		return PTR_ERR(cxlmd);