Re: [RFC PATCH 05/14] PCI: add access functions for PCIe capabilitiesto hide PCIe spec differences

[Jiang Liu]

On 2012-7-11 11:40, Bjorn Helgaas wrote:

>> Good point. Return success when reading unimplemented registeres, that
>> may simplify code. For we still should return -EINVAL when writing
>> unimplemented registers, right?
> 
> Yeah, I guess it's OK to return -EINVAL when *writing* to an
> unimplemented register.  Hopefully the caller is structured such that
> we don't even try to write in that case.  It'd be interesting to audit
> the callers and explore that, but I haven't done that.
Hi Bjorn,
	Seems it would be better to return error code for unimplemented
registers, otherwise following code will becomes more complex. A special
error code for unimplemented registers, such as -EIO?

static void rtl_disable_clock_request(struct pci_dev *pdev)
{
        u16 ctl;

        if (!pci_pcie_capability_read_word(pdev, PCI_EXP_LNKCTL, &ctl)) {
                ctl &= ~PCI_EXP_LNKCTL_CLKREQ_EN;
                pci_pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, ctl);
        }
}

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