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Date: Wed, 11 Jul 2012 14:40:39 +0800
From: Jiang Liu <jiang.liu@huawei.com>
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To: Bjorn Helgaas <bhelgaas@google.com>
CC: Jiang Liu <liuj97@gmail.com>, Don Dutile <ddutile@redhat.com>,
	Yinghai Lu <yinghai@kernel.org>,
	Taku Izumi <izumi.taku@jp.fujitsu.com>,
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	Yijing Wang <wangyijing@huawei.com>,
	Keping Chen <chenkeping@huawei.com>,
	<linux-kernel@vger.kernel.org>, <linux-pci@vger.kernel.org>
Subject: Re: [RFC PATCH 05/14] PCI: add access functions for PCIe capabilities
 to hide PCIe spec differences
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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);
        }
}