On 2012-7-12 1:52, Bjorn Helgaas wrote:
>> 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?
>
> I think you're asking about returning error for *reads* of
> unimplemented registers? I guess I still think it's OK to completely
> hide the v1 nastiness inside these accessors, and return success with
> a zero value when reading. Having several different error returns
> seems like overkill for this case. Nobody wants to distinguish
> between different reasons for failure.
>
> I'm actually not sure that it's worth returning an error even when
> *writing* an unimplemented register. What if we return success and
> just drop the write?
>
> Maybe these should even be void functions. It feels like the only
> real use of the return value is to detect programmer error, and I
> don't think that's very effective. If we remove the return values,
> people will have to focus on the *data*, which seems more important
> anyway.
Hi Bjorn,
It's a little risk to change these PCIe capabilities access
functions as void. On some platform with hardware error detecting/correcting
capabilities, such as EEH on Power, it would be better to return
error code if hardware error happens during accessing configuration registers.
As I know, coming Intel Xeon processor may provide PCIe hardware
error detecting capability similar to EEH on power.
>> 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);
>> }
>> }
>
> I would write that as:
>
> if (!pci_is_pcie(pdev)
> return;
>
> pci_pcie_capability_read_word(pdev, PCI_EXP_LNKCTL, &ctl);
> if (ctl & PCI_EXP_LNKCTL_CLKREQ_EN)
> pci_pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, ctl &
> ~PCI_EXP_LNKCTL_CLKREQ_EN);
>
> which does the right thing regardless of what we do for return values,
> and saves a config write in the case where LNKCTL is implemented and
> CLKREQ_EN is already cleared.
When clearing a flag, we could do that. But if we are trying to set a
flag, it would be better to make sure the target register does exist.
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