Subject: Re: [PATCH v19 01/22] cxl/mem: Arrange for always-synchronous memdev attach

From: Jonathan Cameron <[email-masked]>
Date: Tue, 7 Oct 2025 13:42:24 +0100

On Tue, 7 Oct 2025 13:40:53 +0100
Jonathan Cameron <[email-masked]> wrote:

> On Mon, 6 Oct 2025 11:01:09 +0100
> <[email-masked]> wrote:
> 
> > From: Alejandro Lucero <[email-masked]>
> > 
> > In preparation for CXL accelerator drivers that have a hard dependency on
> > CXL capability initialization, arrange for the endpoint probe result to be
> > conveyed to the caller of devm_cxl_add_memdev().
> > 
> > As it stands cxl_pci does not care about the attach state of the cxl_memdev
> > because all generic memory expansion functionality can be handled by the
> > cxl_core. For accelerators, that driver needs to know perform driver
> > specific initialization if CXL is available, or exectute a fallback to PCIe
> > only operation.
> > 
> > By moving devm_cxl_add_memdev() to cxl_mem.ko it removes async module
> > loading as one reason that a memdev may not be attached upon return from
> > devm_cxl_add_memdev().
> > 
> > The diff is busy as this moves cxl_memdev_alloc() down below the definition
> > of cxl_memdev_fops and introduces devm_cxl_memdev_add_or_reset() to
> > preclude needing to export more symbols from the cxl_core.
> > 
> > Signed-off-by: Dan Williams <[email-masked]>
> 
> Alejandro, SoB chain broken here which makes this currently unmergeable.
> 
> Should definitely have your SoB as you sent the patch to the list and need
> to make a statement that you believe it to be fine to do so (see the Certificate
> of origin stuff in the docs).  Also, From should always be one of the authors.
> If Dan wrote this as the SoB suggests then From should be set to him..
> 
> git commit --amend --author="Dan Williams <[email-masked]>"
> 
> Will fix that up.  Then either you add your SoB on basis you just 'handled'
> the patch but didn't make substantial changes, or your SoB and a Codeveloped-by
> if you did make major changes.  If it is minor stuff you can an
> a sign off with # what changed 
> comment next to it.
> 
> A few minor comments inline.

oops. I see this was part of Dan's series that has merged by now...

Never mind unless you want to take any of the suggested tweaks forwards.

J
> 
> Thanks,
> 
> Jonathan
> 
> 
> > ---
> >  drivers/cxl/Kconfig       |  2 +-
> >  drivers/cxl/core/memdev.c | 97 ++++++++++++++++-----------------------
> >  drivers/cxl/mem.c         | 30 ++++++++++++
> >  drivers/cxl/private.h     | 11 +++++
> >  4 files changed, 82 insertions(+), 58 deletions(-)
> >  create mode 100644 drivers/cxl/private.h
> > 
> > diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> > index 028201e24523..111e05615f09 100644
> > --- a/drivers/cxl/Kconfig
> > +++ b/drivers/cxl/Kconfig
> > @@ -22,6 +22,7 @@ if CXL_BUS
> >  config CXL_PCI
> >  	tristate "PCI manageability"
> >  	default CXL_BUS
> > +	select CXL_MEM
> >  	help
> >  	  The CXL specification defines a "CXL memory device" sub-class in the
> >  	  PCI "memory controller" base class of devices. Device's identified by
> > @@ -89,7 +90,6 @@ config CXL_PMEM
> >  
> >  config CXL_MEM
> >  	tristate "CXL: Memory Expansion"
> > -	depends on CXL_PCI
> >  	default CXL_BUS
> >  	help
> >  	  The CXL.mem protocol allows a device to act as a provider of "System
> > diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> > index c569e00a511f..2bef231008df 100644
> > --- a/drivers/cxl/core/memdev.c
> > +++ b/drivers/cxl/core/memdev.c
> 
> > -
> > -err:
> > -	kfree(cxlmd);
> > -	return ERR_PTR(rc);
> >  }
> > +EXPORT_SYMBOL_NS_GPL(devm_cxl_memdev_add_or_reset, "CXL");
> >  
> >  static long __cxl_memdev_ioctl(struct cxl_memdev *cxlmd, unsigned int cmd,
> >  			       unsigned long arg)
> > @@ -1023,50 +1012,44 @@ static const struct file_operations cxl_memdev_fops = {
> >  	.llseek = noop_llseek,
> >  };
> >  
> > -struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
> > -				       struct cxl_dev_state *cxlds)
> > +struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds)
> >  {
> >  	struct cxl_memdev *cxlmd;
> >  	struct device *dev;
> >  	struct cdev *cdev;
> >  	int rc;
> >  
> > -	cxlmd = cxl_memdev_alloc(cxlds, &cxl_memdev_fops);
> > -	if (IS_ERR(cxlmd))
> > -		return cxlmd;
> > +	cxlmd = kzalloc(sizeof(*cxlmd), GFP_KERNEL);
> 
> It's a little bit non obvious due to the device initialize mid way
> through this, but given there are no error paths after that you can
> currently just do.
> 	struct cxl_memdev *cxlmd __free(kfree) =
> 		cxl_memdev_alloc(cxlds, &cxl_memdev_fops);
> and
> 	return_ptr(cxlmd);
> 
> in the good path.  That lets you then just return rather than having
> the goto err: handling for the error case that currently frees this
> manually.
> 
> Unlike the change below, this one I think is definitely worth making.
> 
> 
> > +	if (!cxlmd)
> > +		return ERR_PTR(-ENOMEM);
> >  
> > -	dev = &cxlmd->dev;
> > -	rc = dev_set_name(dev, "mem%d", cxlmd->id);
> > -	if (rc)
> > +	rc = ida_alloc_max(&cxl_memdev_ida, CXL_MEM_MAX_DEVS - 1, GFP_KERNEL);
> > +	if (rc < 0)
> >  		goto err;
> > -
> > -	/*
> > -	 * Activate ioctl operations, no cxl_memdev_rwsem manipulation
> > -	 * needed as this is ordered with cdev_add() publishing the device.
> > -	 */
> > +	cxlmd->id = rc;
> > +	cxlmd->depth = -1;
> >  	cxlmd->cxlds = cxlds;
> >  	cxlds->cxlmd = cxlmd;
> >  
> > -	cdev = &cxlmd->cdev;
> > -	rc = cdev_device_add(cdev, dev);
> > -	if (rc)
> > -		goto err;
> > +	dev = &cxlmd->dev;
> > +	device_initialize(dev);
> > +	lockdep_set_class(&dev->mutex, &cxl_memdev_key);
> > +	dev->parent = cxlds->dev;
> > +	dev->bus = &cxl_bus_type;
> > +	dev->devt = MKDEV(cxl_mem_major, cxlmd->id);
> > +	dev->type = &cxl_memdev_type;
> > +	device_set_pm_not_required(dev);
> > +	INIT_WORK(&cxlmd->detach_work, detach_memdev);
> >  
> > -	rc = devm_add_action_or_reset(host, cxl_memdev_unregister, cxlmd);
> > -	if (rc)
> > -		return ERR_PTR(rc);
> > +	cdev = &cxlmd->cdev;
> > +	cdev_init(cdev, &cxl_memdev_fops);
> >  	return cxlmd;
> >  
> >  err:
> > -	/*
> > -	 * The cdev was briefly live, shutdown any ioctl operations that
> > -	 * saw that state.
> > -	 */
> > -	cxl_memdev_shutdown(dev);
> > -	put_device(dev);
> > +	kfree(cxlmd);
> >  	return ERR_PTR(rc);
> >  }
> > -EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");
> > +EXPORT_SYMBOL_NS_GPL(cxl_memdev_alloc, "CXL");
> >  
> >  static void sanitize_teardown_notifier(void *data)
> >  {
> > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > index f7dc0ba8905d..144749b9c818 100644
> > --- a/drivers/cxl/mem.c
> > +++ b/drivers/cxl/mem.c
> > @@ -7,6 +7,7 @@
> >  
> >  #include "cxlmem.h"
> >  #include "cxlpci.h"
> > +#include "private.h"
> >  #include "core/core.h"
> >  
> >  /**
> > @@ -203,6 +204,34 @@ static int cxl_mem_probe(struct device *dev)
> >  	return devm_add_action_or_reset(dev, enable_suspend, NULL);
> >  }
> >  
> > +/**
> > + * devm_cxl_add_memdev - Add a CXL memory device
> > + * @host: devres alloc/release context and parent for the memdev
> > + * @cxlds: CXL device state to associate with the memdev
> > + *
> > + * Upon return the device will have had a chance to attach to the
> > + * cxl_mem driver, but may fail if the CXL topology is not ready
> > + * (hardware CXL link down, or software platform CXL root not attached)
> > + */
> > +struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
> > +				       struct cxl_dev_state *cxlds)
> > +{
> > +	struct cxl_memdev *cxlmd = cxl_memdev_alloc(cxlds);
> 
> Bit marginal but you could do a DEFINE_FREE() for cxlmd 
> similar to the one that exists for put_cxl_port
> 
> You would then need to steal the pointer for the devm_ call at the
> end of this function.
> 
> 
> > +	int rc;
> > +
> > +	if (IS_ERR(cxlmd))
> > +		return cxlmd;
> > +
> > +	rc = dev_set_name(&cxlmd->dev, "mem%d", cxlmd->id);
> > +	if (rc) {
> > +		put_device(&cxlmd->dev);
> > +		return ERR_PTR(rc);
> > +	}
> > +
> > +	return devm_cxl_memdev_add_or_reset(host, cxlmd);
> > +}
> > +EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");