linux-kernel - Re: [PATCH v3 1/3] PCI: endpoint: Add helper function pci_epf_get_bar_required

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Message-ID: <aNaHrj0rwLTtSRS3@ryzen>
Date: Fri, 26 Sep 2025 14:31:42 +0200
From: Niklas Cassel <cassel@...nel.org>
To: Frank Li <Frank.Li@....com>
Cc: Manivannan Sadhasivam <mani@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Jon Mason <jdmason@...zu.us>,
	Dave Jiang <dave.jiang@...el.com>, Allen Hubbe <allenbh@...il.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	ntb@...ts.linux.dev, imx@...ts.linux.dev
Subject: Re: [PATCH v3 1/3] PCI: endpoint: Add helper function
 pci_epf_get_bar_required_size()

On Thu, Sep 25, 2025 at 01:01:47PM -0400, Frank Li wrote:
> Introduce pci_epf_get_bar_required_size() to retrieve the required BAR
> size and memory size. Prepare for adding support to set an MMIO address to
> a specific BAR.
> 
> Use two variables 'aligned_bar_size' and 'aligned_mem_size' to avoid
> confuse.

s/confuse/confusion/


> 
> No functional changes.
> 
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
> change in v3
> - change return value to int.
> - use two pointers return bar size aligned and memory start address aligned
> - update comments about why need memory align size. Actually iATU require
> start address match aligned requirement. Since kernel return align to
> size's address.
> - use two varible aligned_bar_size and aligned_mem_size to avoid confuse
> use 'size'.
> 
> change in v2
> - new patch
> ---
>  drivers/pci/endpoint/pci-epf-core.c | 84 +++++++++++++++++++++++--------------
>  1 file changed, 53 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
> index d54e18872aefc07c655c94c104a347328ff7a432..2cd0257831f9885a4381c087ed8f3326f5960966 100644
> --- a/drivers/pci/endpoint/pci-epf-core.c
> +++ b/drivers/pci/endpoint/pci-epf-core.c
> @@ -208,6 +208,49 @@ void pci_epf_remove_vepf(struct pci_epf *epf_pf, struct pci_epf *epf_vf)
>  }
>  EXPORT_SYMBOL_GPL(pci_epf_remove_vepf);
>  
> +static int
> +pci_epf_get_bar_required_size(struct pci_epf *epf, size_t size,
> +			      size_t *aligned_bar_size,
> +			      size_t *aligned_mem_size,
> +			      enum pci_barno bar,
> +			      const struct pci_epc_features *epc_features,
> +			      enum pci_epc_interface_type type)
> +{
> +	u64 bar_fixed_size = epc_features->bar[bar].fixed_size;
> +	size_t align = epc_features->align;
> +
> +	if (size < 128)
> +		size = 128;
> +
> +	/* According to PCIe base spec, min size for a resizable BAR is 1 MB. */
> +	if (epc_features->bar[bar].type == BAR_RESIZABLE && size < SZ_1M)
> +		size = SZ_1M;
> +
> +	if (epc_features->bar[bar].type == BAR_FIXED && bar_fixed_size) {
> +		if (size > bar_fixed_size) {
> +			dev_err(&epf->dev,
> +				"requested BAR size is larger than fixed size\n");
> +			return -ENOMEM;
> +		}
> +		size = bar_fixed_size;
> +	} else {
> +		/* BAR size must be power of two */
> +		size = roundup_pow_of_two(size);
> +	}
> +
> +	*aligned_bar_size = size;

I think this name is wrong.
The BAR size has not been aligned to anything.
The BAR size has to be a power of two, but that is a requirement of the PCI
specification, so that in an inherent property of a BAR.

Perhaps just name it size or bar_size?


Kind regards,
Niklas