Re: [PATCH 01/11] cxl/pci: Add generic MSI-X/MSI irq support

[Ira Weiny]

On Wed, Nov 16, 2022 at 02:53:41PM +0000, Jonathan Cameron wrote:
> On Thu, 10 Nov 2022 10:57:48 -0800
> ira.weiny@xxxxxxxxx wrote:
> 
> > From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> > 
> > Currently the only CXL features targeted for irq support require their
> > message numbers to be within the first 16 entries.  The device may
> > however support less than 16 entries depending on the support it
> > provides.
> > 
> > Attempt to allocate these 16 irq vectors.  If the device supports less
> > then the PCI infrastructure will allocate that number.  Store the number
> > of vectors actually allocated in the device state for later use
> > by individual functions.
> See later patch review, but I don't think we need to store the number
> allocated because any vector is guaranteed to be below that point

Only as long as we stick to those functions which are guaranteed to be under
16.  If a device supports more than 16 and code is added to try and enable that
irq this base support will not cover that.

> (QEMU code is wrong on this at the momemt, but there are very few vectors
>  so it hasn't mattered yet).

How so?  Does the spec state that a device must report at least 16 vectors?

> 
> Otherwise, pcim fun deals with some of the cleanup you are doing again
> here for us so can simplify this somewhat. See inline.

Yea it is broken.

> 
> Jonathan
> 
> 
> 
> > 
> > Upon successful allocation, users can plug in their respective isr at
> > any point thereafter, for example, if the irq setup is not done in the
> > PCI driver, such as the case of the CXL-PMU.
> > 
> > Cc: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> > Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> > Co-developed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> > Signed-off-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> > 
> > ---
> > Changes from Ira
> > 	Remove reviews
> > 	Allocate up to a static 16 vectors.
> > 	Change cover letter
> > ---
> >  drivers/cxl/cxlmem.h |  3 +++
> >  drivers/cxl/cxlpci.h |  6 ++++++
> >  drivers/cxl/pci.c    | 32 ++++++++++++++++++++++++++++++++
> >  3 files changed, 41 insertions(+)
> > 
> > diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> > index 88e3a8e54b6a..b7b955ded3ac 100644
> > --- a/drivers/cxl/cxlmem.h
> > +++ b/drivers/cxl/cxlmem.h
> > @@ -211,6 +211,7 @@ struct cxl_endpoint_dvsec_info {
> >   * @info: Cached DVSEC information about the device.
> >   * @serial: PCIe Device Serial Number
> >   * @doe_mbs: PCI DOE mailbox array
> > + * @nr_irq_vecs: Number of MSI-X/MSI vectors available
> >   * @mbox_send: @dev specific transport for transmitting mailbox commands
> >   *
> >   * See section 8.2.9.5.2 Capacity Configuration and Label Storage for
> > @@ -247,6 +248,8 @@ struct cxl_dev_state {
> >  
> >  	struct xarray doe_mbs;
> >  
> > +	int nr_irq_vecs;
> > +
> >  	int (*mbox_send)(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *cmd);
> >  };
> >  
> > diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
> > index eec597dbe763..b7f4e2f417d3 100644
> > --- a/drivers/cxl/cxlpci.h
> > +++ b/drivers/cxl/cxlpci.h
> > @@ -53,6 +53,12 @@
> >  #define	    CXL_DVSEC_REG_LOCATOR_BLOCK_ID_MASK			GENMASK(15, 8)
> >  #define     CXL_DVSEC_REG_LOCATOR_BLOCK_OFF_LOW_MASK		GENMASK(31, 16)
> >  
> > +/*
> > + * NOTE: Currently all the functions which are enabled for CXL require their
> > + * vectors to be in the first 16.  Use this as the max.
> > + */
> > +#define CXL_PCI_REQUIRED_VECTORS 16
> > +
> >  /* Register Block Identifier (RBI) */
> >  enum cxl_regloc_type {
> >  	CXL_REGLOC_RBI_EMPTY = 0,
> > diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> > index faeb5d9d7a7a..62e560063e50 100644
> > --- a/drivers/cxl/pci.c
> > +++ b/drivers/cxl/pci.c
> > @@ -428,6 +428,36 @@ static void devm_cxl_pci_create_doe(struct cxl_dev_state *cxlds)
> >  	}
> >  }
> >  
> > +static void cxl_pci_free_irq_vectors(void *data)
> > +{
> > +	pci_free_irq_vectors(data);
> > +}
> > +
> > +static void cxl_pci_alloc_irq_vectors(struct cxl_dev_state *cxlds)
> > +{
> > +	struct device *dev = cxlds->dev;
> > +	struct pci_dev *pdev = to_pci_dev(dev);
> > +	int nvecs;
> > +	int rc;
> > +
> > +	nvecs = pci_alloc_irq_vectors(pdev, 1, CXL_PCI_REQUIRED_VECTORS,
> > +				   PCI_IRQ_MSIX | PCI_IRQ_MSI);
> > +	if (nvecs < 0) {
> > +		dev_dbg(dev, "Not enough interrupts; use polling instead.\n");
> > +		return;
> > +	}
> > +
> > +	rc = devm_add_action_or_reset(dev, cxl_pci_free_irq_vectors, pdev);
> The pci managed code always gives me a headache because there is a lot of magic
> under the hood if you ever called pcim_enable_device() which we did.
> 
> Chasing through
> 
> pci_alloc_irq_vectors_affinity()->
> either
> 	__pci_enable_msix_range()
> or
> 	__pci_enable_msi_range()
> 
> they are similar
> 	pci_setup_msi_context()
> 		pci_setup_msi_release()
> 			adds pcmi_msi_release devm action.
> and that frees the vectors for us.
> So we don't need to do it here.

:-/

So what is the point of pci_free_irq_vectors()?  This is very confusing to have
a function not called pcim_* [pci_alloc_irq_vectors()] do 'pcim stuff'.

Ok I'll drop this extra because I see it now.

> 
> 
> > +	if (rc) {
> > +		dev_dbg(dev, "Device managed call failed; interrupts disabled.\n");
> > +		/* some got allocated, clean them up */
> > +		cxl_pci_free_irq_vectors(pdev);
> We could just leave them lying around for devm cleanup to sweep up eventually
> or free them as you have done here.

And besides this extra call is flat out broken.  cxl_pci_free_irq_vectors() is
already called at this point if devm_add_action_or_reset() failed...  But I see
this is not required.

I do plan to add a big ol' comment as to why we don't need to mirror the call
with the corresponding 'free'.

I'll respin,
Ira

> 
> > +		return;
> > +	}
> > +
> > +	cxlds->nr_irq_vecs = nvecs;
> > +}
> > +
> >  static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> >  {
> >  	struct cxl_register_map map;
> > @@ -494,6 +524,8 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> >  	if (rc)
> >  		return rc;
> >  
> > +	cxl_pci_alloc_irq_vectors(cxlds);
> > +
> >  	cxlmd = devm_cxl_add_memdev(cxlds);
> >  	if (IS_ERR(cxlmd))
> >  		return PTR_ERR(cxlmd);
>