linux-kernel - Re: [PATCH 1/2] PCI: endpoint: Enhance pci_epf_alloc_space() and rename to pci_epf_set_inbound

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Message-ID: <udt2t2c43nw5de5q5vu2etknbnhrr3m5mqjk72nuyiurk46kbp@e47e5kvk2m22>
Date: Sat, 30 Aug 2025 20:16:33 +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
Subject: Re: [PATCH 1/2] PCI: endpoint: Enhance pci_epf_alloc_space() and
 rename to pci_epf_set_inbound_space()

On Fri, Aug 15, 2025 at 06:20:53PM GMT, Frank Li wrote:
> Enhance pci_epf_alloc_space() to handle setting any physical address as
> inbound memory space, such as an MSI message base address. The function
> already accounts for different alignment requirements for different BARs,
> so reuse this logic and rename the function to pci_epf_set_inbound_space().
> 

I don't think combining both APIs is a good idea. One allocates space for
inbound memory/populates epf_bar and another reuses existing memory/populates
epf_bar. Combining both, logically makes little sense and another makes the code
messy.

If you want to reuse the alignment checks and epf_bar setting from
pci_epf_alloc_space(), then create a separate helper(s) out of it and call from
both APIs.

> Make pci_epf_alloc_space() inline and call pci_epf_set_inbound_space() with
> from_space set to true to maintain compatibility.
> 
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
> ---
>  drivers/pci/endpoint/pci-epf-core.c | 69 ++++++++++++++++++++++++++++++-------
>  include/linux/pci-epc.h             |  5 ---
>  include/linux/pci-epf.h             | 35 ++++++++++++++++---
>  3 files changed, 87 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
> index d54e18872aefc07c655c94c104a347328ff7a432..5b802b1ea3e28a32e38f4ab6a649cb97a2f29b95 100644
> --- a/drivers/pci/endpoint/pci-epf-core.c
> +++ b/drivers/pci/endpoint/pci-epf-core.c
> @@ -249,20 +249,26 @@ void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar,
>  EXPORT_SYMBOL_GPL(pci_epf_free_space);
>  
>  /**
> - * pci_epf_alloc_space() - allocate memory for the PCI EPF register space
> + * pci_epf_set_inbound_space() - set memory for the PCI EPF inbound address space
>   * @epf: the EPF device to whom allocate the memory
>   * @size: the size of the memory that has to be allocated
>   * @bar: the BAR number corresponding to the allocated register space
>   * @epc_features: the features provided by the EPC specific to this EPF
>   * @type: Identifies if the allocation is for primary EPC or secondary EPC
> + * @from_memory: allocate from system memory
> + * @inbound_addr: Any physical address space such as MSI message address that
> + *                work as inbound address space. from_memory need be false.
>   *
>   * Invoke to allocate memory for the PCI EPF register space.
>   * Flag PCI_BASE_ADDRESS_MEM_TYPE_64 will automatically get set if the BAR
>   * can only be a 64-bit BAR, or if the requested size is larger than 2 GB.
>   */
> -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)
> +int pci_epf_set_inbound_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,
> +			      bool from_memory,
> +			      dma_addr_t inbound_addr)
>  {
>  	u64 bar_fixed_size = epc_features->bar[bar].fixed_size;
>  	size_t aligned_size, align = epc_features->align;
> @@ -270,7 +276,32 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
>  	dma_addr_t phys_addr;
>  	struct pci_epc *epc;
>  	struct device *dev;
> -	void *space;
> +	void *space = NULL;
> +	dma_addr_t up;
> +
> +	up = inbound_addr + size - 1;
> +
> +	/*
> +	 *  Bits:            15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
> +	 *  Inbound_addr:    U  U  U  U  U  U  0 X X X X X X X X X
> +	 *  Up:              U  U  U  U  U  U  1 X X X X X X X X X
> +	 *
> +	 *  U means address bits have not change in Range [Inbound_Addr, Up]
> +	 *  X means bit 0 or 1.
> +	 *
> +	 *  Inbound_addr^Up  0  0  0  0  0  0  1 X X X X X X X X X
> +	 *  Find first bit 1 pos from MSB, 2 ^ pos windows will cover
> +	 *  [Inbound_Addr, Up] range.

On what basis this size calculation is used?

- Mani

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