Re: [PATCH 2/4] PCI: Add pci_rebar_bytes_to_size()

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Jan 07, 2021 at 06:50:15PM +0100, Nirmoy Das wrote:
> Users of pci_resize_resource() need a way to calculate bar size
> from desired bytes. Add a helper function and export it so that
> modular drivers can use it.

s/bar/BAR/

> Signed-off-by: Darren Salt <devspam@moreofthesa.me.uk>
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/pci.c   | 2 +-
>  include/linux/pci.h | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index ef80ed451415..16216186b51c 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1648,7 +1648,7 @@ static void pci_restore_rebar_state(struct pci_dev *pdev)
>  		pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
>  		bar_idx = ctrl & PCI_REBAR_CTRL_BAR_IDX;
>  		res = pdev->resource + bar_idx;
> -		size = ilog2(resource_size(res)) - 20;
> +		size = pci_rebar_bytes_to_size(resource_size(res));
>  		ctrl &= ~PCI_REBAR_CTRL_BAR_SIZE;
>  		ctrl |= size << PCI_REBAR_CTRL_BAR_SHIFT;
>  		pci_write_config_dword(pdev, pos + PCI_REBAR_CTRL, ctrl);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 9999040cfad9..77fed01523e0 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1226,6 +1226,12 @@ void pci_update_resource(struct pci_dev *dev, int resno);
>  int __must_check pci_assign_resource(struct pci_dev *dev, int i);
>  int __must_check pci_reassign_resource(struct pci_dev *dev, int i, resource_size_t add_size, resource_size_t align);
>  void pci_release_resource(struct pci_dev *dev, int resno);
> +static inline int pci_rebar_bytes_to_size(u64 bytes)
> +{
> +	bytes = roundup_pow_of_two(bytes);
> +	return max(ilog2(bytes), 20) - 20;

This isn't returning a "size", is it?  It looks like it's returning
the log2 of the number of MB the BAR will be, i.e., the encoding used
by the Resizable BAR Control register "BAR Size" field.  Needs a brief
comment to that effect and/or a different function name.

> +}
> +
>  u32 pci_rebar_get_possible_sizes(struct pci_dev *pdev, int bar);
>  int __must_check pci_resize_resource(struct pci_dev *dev, int i, int size);
>  int pci_select_bars(struct pci_dev *dev, unsigned long flags);
> -- 
> 2.29.2
>