The offset is absolute and starts at 0. These functions will return an
error if the offset is below 0x40.

I agree the comment can be made clearer.

--Elad

On Tue, 2023-10-17 at 02:07 -0400, Deniz Eren wrote:
> I have a public open-source project that aims to porting of Linux
> CAN-bus drivers to QNX.
> Repository: https://github.com/Deniz-Eren/dev-can-linux
> 
> I have question regarding the offset input parameter of
> pci_device_cfg_rd*() and pci_device_cfg_wr*() series of functions.
> 
> Looking at QNX library file: qnx710/target/qnx7/usr/include/pci/pci.h
> We see comment: "The following functions provide read access to the
> device dependent portion of the 256/4096 byte PCI/PCIe configuration
> space from 0x40 to 0xFF/0xFFF."
> 
> This sounds like the offset input parameter of pci_device_cfg_rd*()
> and pci_device_cfg_wr*() series of functions means offset=0x00 refers
> to the first byte of the configuration space that starts at 0x40 and
> goes through to to 0xFF/0xFFF. However, in practice one of our
> community members found that when they were testing with the
> peak_pci.c driver, that these pci_device_cfg_rd*() and
> pci_device_cfg_wr*() series of functions do not start at 0x40 but
> start at 0x00. So to access the configuration space at 0x40 to
> 0xFF/0xFFF we had to add 0x40 to the address offset to get equivalent
> behaviour as that of the same code running on Linux.
> 
> This peak_pci.c, is one of the drivers we have ported from Linux and
> it's the Peak driver:
> https://github.com/Deniz-Eren/dev-can-linux/blob/main/src/kernel/drivers/net/can/sja1000/peak_pci.c
> 
> At line 590 you see:
>     err = pci_read_config_word(pdev, 0x2e, &sub_sys_id);
>     if (err)
>             goto failure_release_regions;
> 
> At line 597 you see:
>     err = pci_write_config_word(pdev, 0x44, 0);
>     if (err)
>             goto failure_release_regions;
> 
> This peak_pci.c have been taken from the Linux kernel source code as-
> is (https://github.com/torvalds/linux). To interface to QNX we have
> implemented the Linux functions pci_write_config_word() and
> pci_read_config_word() as
> https://github.com/Deniz-Eren/dev-can-linux/blob/main/src/pci.c
> 
> As you can see, in our implementation we had to call
> pci_device_cfg_rd*() and pci_device_cfg_wr*() with a +0x40 for the
> peak_pci.c driver to work properly.
> 
> This means, either the comment block for pci_device_cfg_rd*() and
> pci_device_cfg_wr*() series of functions in file
> qnx710/target/qnx7/usr/include/pci/pci.h is misleading or incorrect
> and it should say 0x00 to 0xFF/0xFFF. Otherwise, the implementation
> of these functions are incorrect and they need to be updated to
> actually give access to 0x40 to 0xFF/0xFFF.
> 
> Any comments?
> 
> 
> 
> _______________________________________________
> 
> OSTech
> http://community.qnx.com/sf/go/post122397
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