Re: [PATCH 3/5] cxl/pci: Add DOE Auxiliary Devices

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Wed, 10 Nov 2021 17:31:23 -0800
Ira Weiny <ira.weiny@intel.com> wrote:

> On Mon, Nov 08, 2021 at 01:09:18PM +0000, Jonathan Cameron wrote:
> > On Fri, 5 Nov 2021 16:50:54 -0700
> > <ira.weiny@intel.com> wrote:
> >   
> > > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > 
> > > CXL devices have DOE mailboxes.  Create auxiliary devices which can be
> > > driven by the generic DOE auxiliary driver.  
> > 
> > I'd like Bjorn's input on the balance here between what is done
> > in cxl/pci.c and what should be in the PCI core code somewhere.
> > 
> > The tricky bit preventing this being done entirely as part of 
> > PCI device instantiation is the interrupts.
> >   
> > > 
> > > Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> > > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>  
> > 
> > Mostly new code, so not sure I should really be listed on this
> > one but I don't mind either way.
> > 
> > A few comments inline but overall this ended up nice and clean.
> >   
> > > 
> > > ---
> > > Changes from V4:
> > > 	Make this an Auxiliary Driver rather than library functions
> > > 	Split this out into it's own patch
> > > 	Base on the new cxl_dev_state structure
> > > 
> > > Changes from Ben
> > > 	s/CXL_DOE_DEV_NAME/DOE_DEV_NAME/
> > > ---
> > >  drivers/cxl/Kconfig |   1 +
> > >  drivers/cxl/cxl.h   |  13 +++++
> > >  drivers/cxl/pci.c   | 120 ++++++++++++++++++++++++++++++++++++++++++++
> > >  3 files changed, 134 insertions(+)
> > > 
> > > diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> > > index 67c91378f2dd..9d53720bea07 100644
> > > --- a/drivers/cxl/Kconfig
> > > +++ b/drivers/cxl/Kconfig
> > > @@ -16,6 +16,7 @@ if CXL_BUS
> > >  config CXL_MEM
> > >  	tristate "CXL.mem: Memory Devices"
> > >  	default CXL_BUS
> > > +	select PCI_DOE_DRIVER
> > >  	help
> > >  	  The CXL.mem protocol allows a device to act as a provider of
> > >  	  "System RAM" and/or "Persistent Memory" that is fully coherent
> > > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> > > index 5e2e93451928..f1241a7f2b7b 100644
> > > --- a/drivers/cxl/cxl.h
> > > +++ b/drivers/cxl/cxl.h
> > > @@ -75,6 +75,19 @@ static inline int cxl_hdm_decoder_count(u32 cap_hdr)
> > >  #define CXLDEV_MBOX_BG_CMD_STATUS_OFFSET 0x18
> > >  #define CXLDEV_MBOX_PAYLOAD_OFFSET 0x20
> > >  
> > > +/*
> > > + * Address space properties derived from:
> > > + * CXL 2.0 8.2.5.12.7 CXL HDM Decoder 0 Control Register
> > > + */
> > > +#define CXL_ADDRSPACE_RAM   BIT(0)
> > > +#define CXL_ADDRSPACE_PMEM  BIT(1)
> > > +#define CXL_ADDRSPACE_TYPE2 BIT(2)
> > > +#define CXL_ADDRSPACE_TYPE3 BIT(3)
> > > +#define CXL_ADDRSPACE_MASK  GENMASK(3, 0)  
> > 
> > Stray.  
> 
> Not sure what you mean here???
> 
> There were a number of defines which were unused but I left them in.
> 
> This came right out of your patch 3.
> 
> https://lore.kernel.org/linux-cxl/20210524133938.2815206-4-Jonathan.Cameron@huawei.com/
> 
> I can remove these defines if you want?

They don't have anything to do with DOE that I can see. Probably a side effect
of a merge that went wrong and I didn't notice!




> > 
> > Normally after device_add() suceeded we only ever call device_del()
> > as per the docs for device_add()
> > https://elixir.bootlin.com/linux/latest/source/drivers/base/core.c#L3277  
> 
> I think you are miss reading that comment.  Here auxiliary_device_add() has
> succeeded.  Therefore both device_del() and put_device() must be called.  In
> the case of auxiliary_device_add() failing we only call
> auxiliary_device_uninit() [put_device()].
> 
> So I think this is correct.
> 
> The other places I spot checked called device_del() _and_ put_device().

Yeah. I had that wrong. Ref counts will be wrong otherwise.


> 
> >   
> > > +}
> > > +
> > > +static DEFINE_IDA(cxl_doe_adev_ida);
> > > +static void __doe_dev_release(struct auxiliary_device *adev)
> > > +{
> > > +	struct pci_doe_dev *doe_dev = container_of(adev, struct pci_doe_dev,
> > > +						   adev);
> > > +
> > > +	ida_free(&cxl_doe_adev_ida, adev->id);
> > > +	kfree(doe_dev);
> > > +}
> > > +
> > > +static void cxl_doe_dev_release(struct device *dev)
> > > +{
> > > +	struct auxiliary_device *adev = container_of(dev,
> > > +						struct auxiliary_device,
> > > +						dev);
> > > +	__doe_dev_release(adev);
> > > +}
> > > +
> > > +static int cxl_setup_doe_devices(struct cxl_dev_state *cxlds)  
> > 
> > Pass in the struct device, or maybe even the struct pci_dev as
> > nothing in here is using the cxl_dev_state.  
> 
> Ah yea can I leave this per the next patch?  Or I can change it then change it
> to cxlds in the next patch.  But I would rather leave it.

I think we will end up reworking this anyway, but maybe there will
still be a cxl_setup_doe_devices wrapper involved.

> 
> >   
> > > +{
> > > +	struct device *dev = cxlds->dev;
> > > +	struct pci_dev *pdev = to_pci_dev(dev);
> > > +	int irqs, rc;
> > > +	u16 pos = 0;
> > > +
> > > +	/*
> > > +	 * An implementation of a cxl type3 device may support an unknown
> > > +	 * number of interrupts. Assume that number is not that large and
> > > +	 * request them all.
> > > +	 */
> > > +	irqs = pci_msix_vec_count(pdev);
> > > +	rc = pci_alloc_irq_vectors(pdev, irqs, irqs, PCI_IRQ_MSIX);
> > > +	if (rc != irqs) {
> > > +		/* No interrupt available - carry on */
> > > +		dev_dbg(dev, "No interrupts available for DOE\n");
> > > +	} else {
> > > +		/*
> > > +		 * Enabling bus mastering could be done within the DOE
> > > +		 * initialization, but as it potentially has other impacts
> > > +		 * keep it within the driver.
> > > +		 */
> > > +		pci_set_master(pdev);
> > > +		rc = devm_add_action_or_reset(dev,
> > > +					      cxl_mem_free_irq_vectors,
> > > +					      pdev);
> > > +		if (rc)
> > > +			return rc;
> > > +	}
> > > +  
> > 
> > Above here is driver specific...
> > Everything from here is is generic so perhaps move it to the PCI core?
> > Alternatively wait until we have users that aren't CXL.  
> 
> I'm still looking for where in the PCI core this would be appropriate to
> place...

Yeah, this needs Bjorn's input. One option would be to move from a soft
dependency to a hard one on the pci-doe module and just put this in there
as an exported utility function.

> 
> >   
> > > +	pos = pci_find_next_ext_capability(pdev, pos, PCI_EXT_CAP_ID_DOE);
> > > +
> > > +	while (pos > 0) {
> > > +		struct auxiliary_device *adev;
> > > +		struct pci_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 = pos;
> > > +
> > > +		/* Set up struct auxiliary_device */
> > > +		adev = &new_dev->adev;
> > > +		id = ida_alloc(&cxl_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_doe_dev_release;
> > > +		adev->dev.parent = dev;
> > > +
> > > +		if (auxiliary_device_init(adev)) {
> > > +			__doe_dev_release(adev);
> > > +			return -EIO;
> > > +		}
> > > +
> > > +		if (auxiliary_device_add(adev)) {
> > > +			auxiliary_device_uninit(adev);
> > > +			return -EIO;
> > > +		}
> > > +
> > > +		rc = devm_add_action_or_reset(dev, cxl_destroy_doe_device, adev);
> > > +		if (rc)
> > > +			return rc;
> > > +
> > > +		if (device_attach(&adev->dev) != 1)
> > > +			dev_err(&adev->dev,
> > > +				"Failed to attach a driver to DOE device %d\n",
> > > +				adev->id);  
> > 
> > I wondered about this and how it would happen.
> > Given soft dependency only between the drivers it's possible but error or info?
> > I'd go with dev_info().  It is an error I'd bail out and used deferred probing
> > to try again when it will succeed.  
> 
> I made this dev_err() on purpose.  And I don't know about the deferred probing.
> Maybe deferred probing on the CDAT read but even that I think is going to be a
> pain.
> 
> The sequence I can think of is:
> 
> cxl_pci loaded
> 	[finds all devices]
> 	[soft loads pci_doe]
> 	[device_attach works]
> Admin unloads pci_doe
> 	[hot-plug new device]
> 	[device_attach fails]
> 	[cdat will fail until driver is loaded]
> 
> I spoke with Dan about this and while this is unfortunate it is what the user
> asked for.  So I prefer dev_err() above to make sure that there is an
> indication of why this device is potentially not going to work.
I'm fine with it being dev_err(), but make it a hard error if it happens.
I don't like potentially not working, and would rather see definitely not
working in this case - so have the function return an error code.

Jonathan
> 
> Thanks for the review,
> Ira
>