Re: [PATCH v3 4/5] PCI/IOV: Allow extending VF BAR within original resource boundary

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Oct 10, 2024 at 12:32:02PM +0200, Michał Winiarski wrote:
> VF MMIO resource reservation, either created by system firmware and
> inherited by Linux PCI subsystem or created by the subsystem itself,
> contains enough space to fit the BAR of all SR-IOV Virtual Functions
> that can potentially be created (total VFs supported by the device).

It's *possible* that this is true, but there's no guarantee that
firmware has assigned enough space for all BARs of all possible VFs.

> This can be leveraged when the device is exposing lower than optimal BAR
> size as a default, allowing access to the entire resource when lower
> number of VFs are created.
> It is achieved by dynamically resizing the BAR to largest possible value
> that allows to fit all newly created VFs within the original resource
> boundary.

Add blank lines between paragraphs.

This log doesn't actually say what the patch does.  It describes a
possible configuration and ways that it may be used, and even *how*
something might be done, but something along the lines of the subject
line should be included in the commit log.

> +static void pci_iov_resource_do_extend(struct pci_dev *dev, int resno, u16 num_vfs)

Please wrap to fit in 80 columns like the rest of the file.

> +int pci_iov_resource_extend(struct pci_dev *dev, int resno, bool enable)

Please add kerneldoc here to help users of this exported function.

> @@ -480,6 +560,11 @@ static ssize_t sriov_numvfs_store(struct device *dev,
>  		goto exit;
>  	}
>  
> +	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {
> +		if (pdev->sriov->rebar_extend[i])
> +			pci_iov_resource_do_extend(pdev, i + PCI_IOV_RESOURCES, num_vfs);

Wrap to fit in 80 columns.

Bjorn