Re: [PATCH] PCI: add helper function to find DVSEC

[Dave Jiang <dave.jiang@intel.com>]

On 10/30/2020 10:35 PM, Randy Dunlap wrote:
> On 10/30/20 3:42 PM, Dave Jiang wrote:
>> Add function that searches for DVSEC and returns the offset in PCI
>> configuration space for the interested DVSEC capability.
>>
>> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
>> Reviewed-by: Ashok Raj <ashok.raj@intel.com>
>> ---
>>
>> The patch has dependency on David Box’s dvsec definition patch:
>> https://lore.kernel.org/linux-pci/bc5f059c5bae957daebde699945c80808286bf45.camel@linux.intel.com/T/#m1d0dc12e3b2c739e2c37106a45f325bb8f001774
>>
>>   drivers/pci/pci.c   |   30 ++++++++++++++++++++++++++++++
>>   include/linux/pci.h |    3 +++
>>   2 files changed, 33 insertions(+)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index 6d4d5a2f923d..49e57b831509 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -589,6 +589,36 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap)
>>   }
>>   EXPORT_SYMBOL_GPL(pci_find_ext_capability);
>>   
>> +/**
>> + * pci_find_dvsec - return position of DVSEC with provided vendor and DVSEC ID
>> + * @dev: the PCI device
>> + * @vendor: vendor for the DVSEC
>> + * @id: the DVSEC capibility ID
> 
>                       capability
> 
>> + *
>> + * Return the offset of DVSEC on success or -ENOTSUPP if not found
> 
>      * Return: the offset of DVSEC on success or -ENOTSUPP if not found
> 
>> + */
>> +int pci_find_dvsec(struct pci_dev *dev, u16 vendor, u16 id)
>> +{
>> +	u16 dev_vendor, dev_id;
>> +	int pos;
>> +
>> +	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DVSEC);
>> +	if (!pos)
>> +		return -ENOTSUPP;
>> +
>> +	while (pos) {
>> +		pci_read_config_word(dev, pos + PCI_DVSEC_HEADER1, &dev_vendor);
>> +		pci_read_config_word(dev, pos + PCI_DVSEC_HEADER2, &dev_id);
>> +		if (dev_vendor == vendor && dev_id == id)
>> +			return pos;
>> +
>> +		pos = pci_find_next_ext_capability(dev, pos, PCI_EXT_CAP_ID_DVSEC);
>> +	}
>> +
>> +	return -ENOTSUPP;
>> +}
>> +EXPORT_SYMBOL_GPL(pci_find_dvsec);
>> +
>>   /**
>>    * pci_get_dsn - Read and return the 8-byte Device Serial Number
>>    * @dev: PCI device to query
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 22207a79762c..6c692d32c82a 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -1069,6 +1069,7 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap);
>>   int pci_find_next_ext_capability(struct pci_dev *dev, int pos, int cap);
>>   int pci_find_ht_capability(struct pci_dev *dev, int ht_cap);
>>   int pci_find_next_ht_capability(struct pci_dev *dev, int pos, int ht_cap);
>> +int pci_find_dvsec(struct pci_dev *dev, u16 vendor, u16 id);
>>   struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
>>   
>>   u64 pci_get_dsn(struct pci_dev *dev);
>> @@ -1726,6 +1727,8 @@ static inline int pci_find_next_capability(struct pci_dev *dev, u8 post,
>>   { return 0; }
>>   static inline int pci_find_ext_capability(struct pci_dev *dev, int cap)
>>   { return 0; }
>> +static inline int pci_find_dvsec(struct pci_dev *dev, u16 vendor, u16 id)
>> +{ return 0; }
> 
> Why shouldn't this return -ENOTSUPP instead of 0?

Actually looking at the other find cap functions. Should I be returning 0 for 
all failures?

> 
>>   
>>   static inline u64 pci_get_dsn(struct pci_dev *dev)
>>   { return 0; }
>>
>>
>