Re: [Xen-devel] [PATCH v4 2/5] lib: devres: add pcim_iomap_wc() variants

[Bjorn Helgaas <bhelgaas@xxxxxxxxxx>]

[+cc linux-pci]

Hi Luis,

On Wed, Apr 29, 2015 at 02:36:09PM -0700, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
> 
> Now that we have pci_iomap_wc() add the respective devres helpers.

I guess I'm still confused about the relationship between pci_iomap_wc()
and arch_phys_wc_add().

Do you expect every caller of pcim_iomap_wc() to also call
arch_phys_wc_add()?

If so, I'm not sure how pcim_iomap_wc() fits into the picture.  A driver
can call both pcim_iomap_wc() and arch_phys_wc_add(), but the driver
doesn't explicitly do the unmap, so where would the arch_phys_wc_del()
happen?

If not, how does a driver know whether it should call arch_phys_wc_add()?

> ...
>  /**
> + * pcim_iomap_wc_regions - Request and iomap PCI BARs with write-combining
> + * @pdev: PCI device to map IO resources for
> + * @mask: Mask of BARs to request and iomap
> + * @name: Name used when requesting regions
> + *
> + * Request and iomap regions specified by @mask with a preference for
> + * write-combining.
> + */
> +int pcim_iomap_wc_regions(struct pci_dev *pdev, int mask, const char *name)
> +{
> +     void __iomem * const *iomap;
> +     int i, rc;
> +
> +     iomap = pcim_iomap_table(pdev);
> +     if (!iomap)
> +             return -ENOMEM;
> +
> +     for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
> +             unsigned long len;
> +
> +             if (!(mask & (1 << i)))
> +                     continue;
> +
> +             rc = -EINVAL;
> +             len = pci_resource_len(pdev, i);
> +             if (!len)
> +                     goto err_inval;
> +
> +             rc = pci_request_region(pdev, i, name);
> +             if (rc)
> +                     goto err_inval;
> +
> +             rc = -ENOMEM;
> +             if (!pcim_iomap_wc(pdev, i, 0))
> +                     goto err_region;

Is there a user for this?  Are there really devices where *all* the BARs
can be mapped with WC?  Are there enough of them to make it worth adding
this?

I don't see users of either pcim_iomap_wc() or pcim_iomap_wc_regions() so
far.  Did I miss them, or do you just expect them in the near future?

Bjorn

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