Re: [PATCH v2 1/5] PCI: endpoint: Add RC-to-EP doorbell support using platform MSI controller

[Kishon Vijay Abraham I <kvijayab@amd.com>]

Hi Frank,

On 9/12/2023 3:39 AM, Frank Li wrote:
> This commit introduces a common method for sending messages from the Root
> Complex (RC) to the Endpoint (EP) by utilizing the platform MSI interrupt
> controller, such as ARM GIC, as an EP doorbell. Maps the memory assigned
> for the BAR region by the PCI host to the message address of the platform
> MSI interrupt controller in the PCI EP. As a result, when the PCI RC writes
> to the BAR region, it triggers an IRQ at the EP. This implementation serves
> as a common method for all endpoint function drivers.

This would help avoid the polling used in current EPF drivers. Thanks!
> 
> However, it currently supports only one EP physical function due to
> limitations in ARM MSI/IMS readiness.

Any such platform or architecture restrictions should not be handled in 
the endpoint core layer.
> 
> Signed-off-by: Frank Li <Frank.Li@nxp.com>
> ---
>   drivers/pci/endpoint/pci-epc-core.c | 192 ++++++++++++++++++++++++++++
>   drivers/pci/endpoint/pci-epf-core.c |  44 +++++++
>   include/linux/pci-epc.h             |   6 +
>   include/linux/pci-epf.h             |   7 +
>   4 files changed, 249 insertions(+)
> 
> diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> index 5a4a8b0be6262..d336a99c6a94f 100644
> --- a/drivers/pci/endpoint/pci-epc-core.c
> +++ b/drivers/pci/endpoint/pci-epc-core.c
> @@ -10,6 +10,7 @@
>   #include <linux/slab.h>
>   #include <linux/module.h>
>   
> +#include <linux/msi.h>
>   #include <linux/pci-epc.h>
>   #include <linux/pci-epf.h>
>   #include <linux/pci-ep-cfs.h>
> @@ -783,6 +784,197 @@ void pci_epc_bme_notify(struct pci_epc *epc)
>   }
>   EXPORT_SYMBOL_GPL(pci_epc_bme_notify);
>   
> +/**
> + * pci_epc_alloc_doorbell() - alloc an address space to let RC trigger EP side IRQ by write data to
> + *			      the space.
> + *
> + * @epc: the EPC device that need doorbell address and data from RC.
> + * @func_no: the physical endpoint function number in the EPC device.
> + * @vfunc_no: the virtual endpoint function number in the physical function.
> + * @num_msgs: the total number of doorbell messages
> + *
> + * Return: 0 success, other is failure
> + */
> +int pci_epc_alloc_doorbell(struct pci_epc *epc, u8 func_no, u8 vfunc_no, int num_msgs)
> +{
> +	int ret;
> +
> +	if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
> +		return -EINVAL;
> +
> +	if (vfunc_no > 0 && (!epc->max_vfs || vfunc_no > epc->max_vfs[func_no]))
> +		return -EINVAL;
> +
> +	if (!epc->ops->alloc_doorbell)
> +		return 0;
> +
> +	mutex_lock(&epc->lock);
> +	ret = epc->ops->alloc_doorbell(epc, func_no, vfunc_no, num_msgs);
> +	mutex_unlock(&epc->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(pci_epc_alloc_doorbell);
> +
> +/**
> + * pci_epc_free_doorbell() - free resource allocated by pci_epc_alloc_doorbell()
> + *
> + * @epc: the EPC device that need doorbell address and data from RC.
> + * @func_no: the physical endpoint function number in the EPC device.
> + * @vfunc_no: the virtual endpoint function number in the physical function.
> + *
> + * Return: 0 success, other is failure
> + */
> +void pci_epc_free_doorbell(struct pci_epc *epc, u8 func_no, u8 vfunc_no)
> +{
> +	if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
> +		return;
> +
> +	if (vfunc_no > 0 && (!epc->max_vfs || vfunc_no > epc->max_vfs[func_no]))
> +		return;
> +
> +	if (!epc->ops->free_doorbell)
> +		return;
> +
> +	mutex_lock(&epc->lock);
> +	epc->ops->free_doorbell(epc, func_no, vfunc_no);
> +	mutex_unlock(&epc->lock);
> +}
> +EXPORT_SYMBOL_GPL(pci_epc_free_doorbell);
> +
> +static irqreturn_t pci_epf_generic_doorbell_handler(int irq, void *data)
> +{
> +	struct pci_epf *epf = data;
> +
> +	if (epf->event_ops && epf->event_ops->doorbell)
> +		epf->event_ops->doorbell(epf, irq - epf->virq_base);
> +
> +	return IRQ_HANDLED;
> +}

IMO the handler should be directly implemented in the EPF drivers. There 
should be one API which returns the virq and the msi_msg to the EPF 
driver and the EPF driver should do request_irq.
> +
> +static void pci_epc_generic_write_msi_msg(struct msi_desc *desc, struct msi_msg *msg)
> +{
> +	struct pci_epc *epc = NULL;
> +	struct class_dev_iter iter;
> +	struct pci_epf *epf;
> +	struct device *dev;
> +
> +	class_dev_iter_init(&iter, pci_epc_class, NULL, NULL);
> +	while ((dev = class_dev_iter_next(&iter))) {
> +		if (dev->parent != desc->dev)
> +			continue;

Ideally the msi_desc should be associated directly with the EPF device.
> +
> +		epc = to_pci_epc(dev);
> +
> +		class_dev_iter_exit(&iter);
> +		break;
> +	}
> +
> +	if (!epc)
> +		return;
> +
> +	/* Only support one EPF for doorbell */
> +	epf = list_first_entry_or_null(&epc->pci_epf, struct pci_epf, list);
> +
> +	if (!epf)
> +		return;

If this is a platform restriction, this should be moved elsewhere.
> +
> +	if (epf->msg && desc->msi_index < epf->num_msgs)
> +		epf->msg[desc->msi_index] = *msg;
> +}
> +
> +
> +/**
> + * pci_epc_generic_alloc_doorbell() - Common help function. Allocate address space from MSI
> + *                                    controller
> + *
> + * @epc: the EPC device that need doorbell address and data from RC.
> + * @func_no: the physical endpoint function number in the EPC device.
> + * @vfunc_no: the virtual endpoint function number in the physical function.
> + * @num_msgs: the total number of doorbell messages
> + *
> + * Remark: use this function only if EPC driver just register one EPC device.
> + *
> + * Return: 0 success, other is failure
> + */
> +int pci_epc_generic_alloc_doorbell(struct pci_epc *epc, u8 func_no, u8 vfunc_no, int num_msgs)
> +{
> +	struct pci_epf *epf;
> +	struct device *dev;
> +	int virq, last;
> +	int ret;
> +	int i;
> +
> +	if (IS_ERR_OR_NULL(epc))
> +		return -EINVAL;
> +
> +	/* Currently only support one func and one vfunc for doorbell */
> +	if (func_no || vfunc_no)
> +		return -EINVAL;
> +
> +	epf = list_first_entry_or_null(&epc->pci_epf, struct pci_epf, list);
> +	if (!epf)
> +		return -EINVAL;
> +
> +	dev = epc->dev.parent;
> +	ret = platform_msi_domain_alloc_irqs(dev, num_msgs, pci_epc_generic_write_msi_msg);
> +	if (ret) {
> +		dev_err(dev, "Failed to allocate MSI\n");
> +		return -ENOMEM;
> +	}

The alloc_irqs should be for a EPF device IMO.
> +
> +	last = -1;
> +	for (i = 0; i < num_msgs; i++) {
> +		virq = msi_get_virq(dev, i);
> +		if (i == 0)
> +			epf->virq_base = virq;
> +
> +		ret = request_irq(virq, pci_epf_generic_doorbell_handler, 0,
> +				  kasprintf(GFP_KERNEL, "pci-epc-doorbell%d", i), epf);
> +
> +		if (ret) {
> +			dev_err(dev, "Failed to request doorbell\n");
> +			goto err_free_irq;
> +		}
> +		last = i;
> +	}
> +
> +	return 0;
> +
> +err_free_irq:
> +	for (i = 0; i < last; i++)
> +		kfree(free_irq(epf->virq_base + i, epf));
> +	platform_msi_domain_free_irqs(dev);
> +
> +	return -EINVAL;
> +}

Thanks,
Kishon