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

Koralahalli Channabasappa, Smita
2025-10-30T19:57:25Z

Hi Alejandro,

I need patches 1–3 from this series as prerequisites for the
Soft-Reserved coordination work, so I wanted to check in on your plans
for the next revision.

Link to the discussion:
https://lore.kernel.org/all/aPbOfFPIhtu5npaG@aschofie-mobl2.lan/

Are patches 1–3 already being updated as part of your v20 work?
If so, I can wait and pick them up from v20 directly.

If v20 is still in progress and may take some time, I can probably carry
patches 1–3 at the start of my series, and if that helps, I can fold in
the review comments by Jonathan while keeping authorship as is. I would
only adjust wording in the commit descriptions to reflect the
Soft-Reserved coordination context.

Alternatively, if you prefer to continue carrying them in the Type-2
series, I can simply reference them as prerequisites instead.

I’m fine with either approach just trying to avoid duplicated effort and
keep review in one place.

Thanks
Smita

On 10/29/2025 4:20 AM, Alejandro Lucero Palau wrote:
>
> On 10/7/25 13:40, Jonathan Cameron wrote:
>> On Mon, 6 Oct 2025 11:01:09 +0100
>> <alejandro.lucero-palau@amd.com> wrote:
>>
>>> From: Alejandro Lucero <alucerop@amd.com>
>>>
>>> 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 <dan.j.williams@intel.com>
>> 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 <dan.j.williams@intel.com>"
>>
>> 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.
>
>
> Understood. I'll ask Dan what he prefers.
>
>
>>
>> A few minor comments inline.
>>
>> 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.
>
>
> I agree so I'll do it. The below suggestion is also needed ...
>
>
>>
>>> +    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.
>
>
> We are not freeing cxlmd in case of errors after we got the allocation,
> so I think it makes sense.
>
>
> Thank you.
>
>
>>
>>> +    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");
>