linux-kernel - Re: [PATCH v2 1/3] PCI: endpoint: Add helper function pci_epf_get_bar_required

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Message-ID: <qg75qzd34b3bxmqn46g4iefd5x2icdmentg34bep2b55jniq7r@ofwzmgy2l7hj>
Date: Wed, 24 Sep 2025 22:47:27 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Frank Li <Frank.Li@....com>
Cc: 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 v2 1/3] PCI: endpoint: Add helper function
 pci_epf_get_bar_required_size()

On Mon, Sep 15, 2025 at 06:22:44PM -0400, Frank Li wrote:
> Introduce pci_epf_get_bar_required_size() to retrieve the required BAR
> size. Prepare for adding support to set an MMIO address to a specific BAR.
> 
> No functional changes.
> 
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
> change in v2
> - new patch
> ---
>  drivers/pci/endpoint/pci-epf-core.c | 52 ++++++++++++++++++++++++-------------
>  1 file changed, 34 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
> index d54e18872aefc07c655c94c104a347328ff7a432..4281067d4a62da6fbf6c2fb807b0f1b5afd1f45b 100644
> --- a/drivers/pci/endpoint/pci-epf-core.c
> +++ b/drivers/pci/endpoint/pci-epf-core.c
> @@ -248,6 +248,36 @@ void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar,
>  }
>  EXPORT_SYMBOL_GPL(pci_epf_free_space);
>  
> +static size_t

s/size_t/int to return errno.

> +pci_epf_get_bar_required_size(struct pci_epf *epf, size_t size,

Rename this helper to pci_epf_align_bar_size() and pass 'size' pointer.

> +			      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;
> +
> +	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 0;

Return value of 0 should not be considered as an error. Return the errno here,
which is -ENOMEM.

> +		}
> +		size = bar_fixed_size;
> +	} else {
> +		/* BAR size must be power of two */
> +		size = roundup_pow_of_two(size);
> +	}
> +
> +	return size;

return 0;

> +}
> +
>  /**
>   * pci_epf_alloc_space() - allocate memory for the PCI EPF register space
>   * @epf: the EPF device to whom allocate the memory
> @@ -264,7 +294,6 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t 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 aligned_size, align = epc_features->align;
>  	struct pci_epf_bar *epf_bar;
>  	dma_addr_t phys_addr;
> @@ -272,24 +301,11 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
>  	struct device *dev;
>  	void *space;
>  
> -	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;
> +	size = pci_epf_get_bar_required_size(epf, size, bar,
> +					     epc_features, type);
>  
> -	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 NULL;
> -		}
> -		size = bar_fixed_size;
> -	} else {
> -		/* BAR size must be power of two */
> -		size = roundup_pow_of_two(size);
> -	}
> +	if (size == 0)
> +		return NULL;

	int ret;

	ret = pci_epf_align_bar_size(..., &size, ...);
	if (ret < 0)
		return NULL;

- Mani

-- 
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