linux-kernel - Re: [PATCH v2] PCI: Add quirk for HiSilicon NP 5896 devices

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Message-ID: <CABhMZUX8spN93es+qtZWtMSUi3M+c99649ect4ZAkcrPLqfO=g@mail.gmail.com>
Date:   Tue, 10 Dec 2019 22:10:12 -0600
From:   Bjorn Helgaas <bjorn.helgaas@...il.com>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, andrew.murray@....com,
        linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        wangkefeng.wang@...wei.com, huawei.libin@...wei.com,
        guohanjun@...wei.com
Subject: Re: [PATCH v2] PCI: Add quirk for HiSilicon NP 5896 devices

On Tue, Dec 10, 2019 at 9:28 PM Xiongfeng Wang
<wangxiongfeng2@...wei.com> wrote:
>
>
>
> On 2019/12/7 2:10, Bjorn Helgaas wrote:
> > On Fri, Dec 06, 2019 at 03:01:45PM +0800, Xiongfeng Wang wrote:
> >> HiSilicon PCI Network Processor 5896 devices misreport the class type as
> >> 'NOT_DEFINED', but it is actually a network device. Also the size of
> >> BAR3 is reported as 265T, but this BAR is actually unused.
> >> This patch modify the class type to 'CLASS_NETWORK' and disable the
> >> unused BAR3.
> >
> > "NOT_DEFINED" is not the value in the Class Code register.  The commit
> > message should include the actual value.
>
> The actual value is 0, I will update the commit message.
>
> >
> >> Signed-off-by: Xiongfeng Wang <wangxiongfeng2@...wei.com>
> >> ---
> >>  drivers/pci/quirks.c    | 29 +++++++++++++++++++++++++++++
> >>  include/linux/pci_ids.h |  1 +
> >>  2 files changed, 30 insertions(+)
> >>
> >> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> >> index 4937a08..b9adebb 100644
> >> --- a/drivers/pci/quirks.c
> >> +++ b/drivers/pci/quirks.c
> >> @@ -5431,3 +5431,32 @@ static void quirk_reset_lenovo_thinkpad_p50_nvgpu(struct pci_dev *pdev)
> >>  DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_NVIDIA, 0x13b1,
> >>                            PCI_CLASS_DISPLAY_VGA, 8,
> >>                            quirk_reset_lenovo_thinkpad_p50_nvgpu);
> >> +
> >> +static void quirk_hisi_fixup_np_class(struct pci_dev *pdev)
> >> +{
> >> +    u32 class = pdev->class;
> >> +
> >> +    pdev->class = PCI_BASE_CLASS_NETWORK << 8;
> >> +    pci_info(pdev, "PCI class overriden (%#08x -> %#08x)\n",
> >> +             class, pdev->class);
> >> +}
> >> +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_HUAWEI, PCI_DEVICE_ID_HISI_5896,
> >> +                    quirk_hisi_fixup_np_class);
> >> +
> >> +/*
> >> + * HiSilicon NP 5896 devices BAR3 size is reported as 256T and causes problem
> >> + * when assigning the resources. But this BAR is actually unused by the driver,
> >> + * so let's disable it.
> >
> > The question is not whether the BAR is used by the driver; the
> > question is whether the device responds to accesses to the region
> > described by the BAR when PCI_COMMAND_MEMORY is turned on.
>
> I asked the hardware engineer. He said I can not write an address into that BAR.

If the BAR is not writable, I think sizing should fail, so I suspect
some of the bits are actually writable.

What do you see in dmesg when this device is enumerated?  Can you
instrument the code in __pci_read_base() and see what we read/write to
that BAR?

Per spec, if the BAR is not implemented, it should be read-only zero.
But obviously the whole reason for the quirk is that the device
doesn't comply with the spec.

Bjorn