Date:   Fri, 29 Apr 2022 16:55:02 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     <ira.weiny@...el.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alison Schofield <alison.schofield@...el.com>,
        "Vishal Verma" <vishal.l.verma@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
        <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V8 04/10] cxl/pci: Create auxiliary devices for each DOE
 mailbox

On Thu, 14 Apr 2022 13:32:31 -0700
ira.weiny@...el.com wrote:

> From: Ira Weiny <ira.weiny@...el.com>
> 
> CXL kernel drivers optionally need to access DOE mailbox capabilities.
> Access to mailboxes for things such as CDAT, SPDM, and IDE are needed by
> the kernel while other access is designed towards user space usage.  An
> example of this is for CXL Compliance Testing (see CXL 2.0 14.16.4
> Compliance Mode DOE) which offers a mechanism to set different test
> modes for a device.
> 
> There is no anticipated need for the kernel to share an individual
> mailbox with user space.  Thus developing an interface to marshal access
> between the kernel and user space for a single mailbox is unnecessary
> overhead.  However, having the kernel relinquish some mailboxes to be
> controlled by user space is a reasonable compromise to share access to
> the device.
> 
> The auxiliary bus provides an elegant solution for this.  Each DOE
> capability is given its own auxiliary device.  This device is controlled
> by a kernel driver by default which restricts access to the mailbox.
> Unbinding the driver from a single auxiliary device (DOE mailbox
> capability) frees the mailbox for user space access.  This architecture
> also allows a clear picture on which mailboxes are kernel controlled vs
> not.
> 
> Iterate each DOE mailbox capability and create auxiliary bus devices.
> Follow on patches will define a driver for the newly created devices.
> 
> sysfs shows the devices.
> 
> $ ls -l /sys/bus/auxiliary/devices/
> total 0
> lrwxrwxrwx 1 root root 0 Mar 24 10:47 cxl_pci.doe.0 -> ../../../devices/pci0000:bf/0000:bf:00.0/0000:c0:00.0/cxl_pci.doe.0
> lrwxrwxrwx 1 root root 0 Mar 24 10:47 cxl_pci.doe.1 -> ../../../devices/pci0000:bf/0000:bf:01.0/0000:c1:00.0/cxl_pci.doe.1
> lrwxrwxrwx 1 root root 0 Mar 24 10:47 cxl_pci.doe.2 -> ../../../devices/pci0000:35/0000:35:00.0/0000:36:00.0/cxl_pci.doe.2
> lrwxrwxrwx 1 root root 0 Mar 24 10:47 cxl_pci.doe.3 -> ../../../devices/pci0000:35/0000:35:01.0/0000:37:00.0/cxl_pci.doe.3
> lrwxrwxrwx 1 root root 0 Mar 24 10:47 cxl_pci.doe.4 -> ../../../devices/pci0000:35/0000:35:00.0/0000:36:00.0/cxl_pci.doe.4
> lrwxrwxrwx 1 root root 0 Mar 24 10:47 cxl_pci.doe.5 -> ../../../devices/pci0000:bf/0000:bf:00.0/0000:c0:00.0/cxl_pci.doe.5
> lrwxrwxrwx 1 root root 0 Mar 24 10:47 cxl_pci.doe.6 -> ../../../devices/pci0000:35/0000:35:01.0/0000:37:00.0/cxl_pci.doe.6
> lrwxrwxrwx 1 root root 0 Mar 24 10:47 cxl_pci.doe.7 -> ../../../devices/pci0000:bf/0000:bf:01.0/0000:c1:00.0/cxl_pci.doe.7
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

oops. I just replied to v7. The point still stands though.
Repeated briefly below.

> 
> ---
> Changes from V7:
> 	Minor code clean ups
> 	Rebased on cxl-pending
> 
> Changes from V6:
> 	Move all the auxiliary device stuff to the CXL layer
> 
> Changes from V5:
> 	Split the CXL specific stuff off from the PCI DOE create
> 	auxiliary device code.
> ---
>  drivers/cxl/Kconfig  |   1 +
>  drivers/cxl/cxlpci.h |  21 +++++++
>  drivers/cxl/pci.c    | 127 +++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 149 insertions(+)
> 
> diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> index f64e3984689f..ac0f5ca95431 100644
> --- a/drivers/cxl/Kconfig
> +++ b/drivers/cxl/Kconfig
> @@ -16,6 +16,7 @@ if CXL_BUS
>  config CXL_PCI
>  	tristate "PCI manageability"
>  	default CXL_BUS
> +	select AUXILIARY_BUS
>  	help
>  	  The CXL specification defines a "CXL memory device" sub-class in the
>  	  PCI "memory controller" base class of devices. Device's identified by
> diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
> index 329e7ea3f36a..2ad8715173ce 100644
> --- a/drivers/cxl/cxlpci.h
> +++ b/drivers/cxl/cxlpci.h
> @@ -2,6 +2,7 @@
>  /* Copyright(c) 2020 Intel Corporation. All rights reserved. */
>  #ifndef __CXL_PCI_H__
>  #define __CXL_PCI_H__
> +#include <linux/auxiliary_bus.h>
>  #include <linux/pci.h>
>  #include "cxl.h"
>  
> @@ -72,4 +73,24 @@ static inline resource_size_t cxl_regmap_to_base(struct pci_dev *pdev,
>  }
>  
>  int devm_cxl_port_enumerate_dports(struct cxl_port *port);
> +
> +/**
> + * struct cxl_doe_dev - CXL DOE auxiliary bus device
> + *
> + * @adev: Auxiliary bus device
> + * @pdev: PCI device this belongs to
> + * @cap_offset: Capability offset
> + * @use_irq: Set if IRQs are to be used with this mailbox
> + *
> + * This represents a single DOE mailbox device.  CXL devices should create this
> + * device and register it on the Auxiliary bus for the CXL DOE driver to drive.
> + */
> +struct cxl_doe_dev {
> +	struct auxiliary_device adev;
> +	struct pci_dev *pdev;
> +	int cap_offset;
> +	bool use_irq;
> +};
> +#define DOE_DEV_NAME "doe"
> +
>  #endif /* __CXL_PCI_H__ */
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index e7ab9a34d718..41a6f3eb0a5c 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -8,6 +8,7 @@
>  #include <linux/mutex.h>
>  #include <linux/list.h>
>  #include <linux/pci.h>
> +#include <linux/pci-doe.h>
>  #include <linux/io.h>
>  #include "cxlmem.h"
>  #include "cxlpci.h"
> @@ -564,6 +565,128 @@ static void cxl_dvsec_ranges(struct cxl_dev_state *cxlds)
>  	info->ranges = __cxl_dvsec_ranges(cxlds, info);
>  }
>  
> +static void cxl_pci_free_irq_vectors(void *data)
> +{
> +	pci_free_irq_vectors(data);
> +}
> +
> +static DEFINE_IDA(pci_doe_adev_ida);
> +
> +static void cxl_pci_doe_dev_release(struct device *dev)
> +{
> +	struct auxiliary_device *adev = container_of(dev,
> +						struct auxiliary_device,
> +						dev);
> +	struct cxl_doe_dev *doe_dev = container_of(adev, struct cxl_doe_dev,
> +						   adev);
> +
> +	ida_free(&pci_doe_adev_ida, adev->id);
> +	kfree(doe_dev);
> +}
> +
> +static void cxl_pci_doe_destroy_device(void *ad)
> +{
> +	auxiliary_device_delete(ad);
> +	auxiliary_device_uninit(ad);
> +}
> +
> +/**
> + * cxl_pci_create_doe_devices - Create auxiliary bus DOE devices for all DOE
> + *				mailboxes found
> + *
> + * @pci_dev: The PCI device to scan for DOE mailboxes
> + *
> + * There is no coresponding destroy of these devices.  This function associates
> + * the DOE auxiliary devices created with the pci_dev passed in.  That
> + * association is device managed (devm_*) such that the DOE auxiliary device
> + * lifetime is always less than or equal to the lifetime of the pci_dev.
> + *
> + * RETURNS: 0 on success -ERRNO on failure.
> + */
> +static int cxl_pci_create_doe_devices(struct pci_dev *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	bool use_irq = true;
> +	int irqs = 0;
> +	u16 off = 0;
> +	int rc;
> +
> +	pci_doe_for_each_off(pdev, off)
> +		irqs++;
I believe this is insufficient because there may be other irqs in use
on the device.  In a similar fashion to that done in pcie/portdrv_core.c
I think we need to instead find the maximum msi/msix vector number
by reading the config space.  Then we request one more vector
than that max value to ensure the vector we need has been requested.

Jonathan

> +	pci_info(pdev, "Found %d DOE mailbox's\n", irqs);
> +
> +	/*
> +	 * Allocate enough vectors for the DOE's
> +	 */
> +	rc = pci_alloc_irq_vectors(pdev, irqs, irqs, PCI_IRQ_MSI |
> +						     PCI_IRQ_MSIX);
> +	if (rc != irqs) {
> +		pci_err(pdev,
> +			"Not enough interrupts for all the DOEs; use polling\n");
> +		use_irq = false;
> +		/* Some got allocated; clean them up */
> +		if (rc > 0)
> +			cxl_pci_free_irq_vectors(pdev);
> +	} else {
> +		/*
> +		 * Enabling bus mastering is require for MSI/MSIx.  It could be
> +		 * done later within the DOE initialization, but as it
> +		 * potentially has other impacts keep it here when setting up
> +		 * the IRQ's.
> +		 */
> +		pci_set_master(pdev);
> +		rc = devm_add_action_or_reset(dev,
> +					      cxl_pci_free_irq_vectors,
> +					      pdev);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	pci_doe_for_each_off(pdev, off) {
> +		struct auxiliary_device *adev;
> +		struct cxl_doe_dev *new_dev;
> +		int id;
> +
> +		new_dev = kzalloc(sizeof(*new_dev), GFP_KERNEL);
> +		if (!new_dev)
> +			return -ENOMEM;
> +
> +		new_dev->pdev = pdev;
> +		new_dev->cap_offset = off;
> +		new_dev->use_irq = use_irq;
> +
> +		/* Set up struct auxiliary_device */
> +		adev = &new_dev->adev;
> +		id = ida_alloc(&pci_doe_adev_ida, GFP_KERNEL);
> +		if (id < 0) {
> +			kfree(new_dev);
> +			return -ENOMEM;
> +		}
> +
> +		adev->id = id;
> +		adev->name = DOE_DEV_NAME;
> +		adev->dev.release = cxl_pci_doe_dev_release;
> +		adev->dev.parent = dev;
> +
> +		if (auxiliary_device_init(adev)) {
> +			cxl_pci_doe_dev_release(&adev->dev);
> +			return -EIO;
> +		}
> +
> +		if (auxiliary_device_add(adev)) {
> +			auxiliary_device_uninit(adev);
> +			return -EIO;
> +		}
> +
> +		rc = devm_add_action_or_reset(dev, cxl_pci_doe_destroy_device,
> +					      adev);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	return 0;
> +}
> +
>  static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  {
>  	struct cxl_register_map map;
> @@ -630,6 +753,10 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	if (rc)
>  		return rc;
>  
> +	rc = cxl_pci_create_doe_devices(pdev);
> +	if (rc)
> +		return rc;
> +
>  	cxl_dvsec_ranges(cxlds);
>  
>  	cxlmd = devm_cxl_add_memdev(cxlds);

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