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

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Message-ID: <016e1a37-ca63-4ecb-9e55-eb701f789e9d@163.com>
Date: Tue, 3 Jun 2025 23:40:43 +0800
From: Hans Zhang <18255117159@....com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.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 2025/6/3 17:18, Ilpo Järvinen wrote:
> 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.
> 

Dear Ilpo,

Thank you very much for your reply. Will change.

I will send the next version after v6.16.

Best regards,
Hans

>> +
>> +	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 */
>>   
>>
>