linux-kernel - Re: [PATCH v12 1/6] PCI: Introduce generic bus config read helper function

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Message-ID: <d6eeb0b5-53b3-5c40-00df-f79aa2619711@linux.intel.com>
Date: Tue, 3 Jun 2025 12:18:39 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Hans Zhang <18255117159@....com>
cc: lpieralisi@...nel.org, bhelgaas@...gle.com, 
    manivannan.sadhasivam@...aro.org, kw@...ux.com, cassel@...nel.org, 
    robh@...nel.org, jingoohan1@...il.com, linux-pci@...r.kernel.org, 
    LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 1/6] PCI: Introduce generic bus config read helper
 function

On Thu, 15 May 2025, Hans Zhang wrote:

> The primary PCI config space accessors are tied to the size of the read
> (byte/word/dword). Upcoming refactoring of PCI capability discovery logic
> requires passing a config accessor function that must be able to perform
> read with different sizes.
> 
> Add any size config space read accessor pci_bus_read_config() to allow
> giving it as the config space accessor to the upcoming PCI capability
> discovery macro.
> 
> Reconstructs the PCI function discovery logic to prepare for unified
> configuration of access modes. No function changes are intended.
> 
> Signed-off-by: Hans Zhang <18255117159@....com>
> ---
> Changes since v9 ~ v11:
> - None
> 
> Changes since v8:
> - The new split is patch 1/6.
> - The patch commit message were modified.
> ---
>  drivers/pci/access.c | 17 +++++++++++++++++
>  drivers/pci/pci.h    |  2 ++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index b123da16b63b..603332658ab3 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -85,6 +85,23 @@ EXPORT_SYMBOL(pci_bus_write_config_byte);
>  EXPORT_SYMBOL(pci_bus_write_config_word);
>  EXPORT_SYMBOL(pci_bus_write_config_dword);
>  
> +int pci_bus_read_config(void *priv, unsigned int devfn, int where, u32 size,
> +			u32 *val)
> +{
> +	struct pci_bus *bus = priv;
> +	int ret;
> +
> +	if (size == 1)
> +		ret = pci_bus_read_config_byte(bus, devfn, where, (u8 *)val);
> +	else if (size == 2)
> +		ret = pci_bus_read_config_word(bus, devfn, where, (u16 *)val);
> +	else
> +		ret = pci_bus_read_config_dword(bus, devfn, where, val);

Perhaps this should check also size == 4 and return 
PCIBIOS_BAD_REGISTER_NUMBER in case size is wrong.

> +
> +	return ret;


> +}
> +EXPORT_SYMBOL_GPL(pci_bus_read_config);

Does this even need to be exported? Isn't the capability search always 
built in?

>  int pci_generic_config_read(struct pci_bus *bus, unsigned int devfn,
>  			    int where, int size, u32 *val)
>  {
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index b81e99cd4b62..5e1477d6e254 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -88,6 +88,8 @@ extern bool pci_early_dump;
>  bool pcie_cap_has_lnkctl(const struct pci_dev *dev);
>  bool pcie_cap_has_lnkctl2(const struct pci_dev *dev);
>  bool pcie_cap_has_rtctl(const struct pci_dev *dev);
> +int pci_bus_read_config(void *priv, unsigned int devfn, int where, u32 size,
> +			u32 *val);
>  
>  /* Functions internal to the PCI core code */
>  
> 

-- 
 i.