linux-kernel - Re: [PATCH v1 2/3] drivers/perf: add DesignWare PCIe PMU driver

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Date:   Mon, 26 Sep 2022 12:18:57 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        rdunlap@...radead.org, robin.murphy@....com, mark.rutland@....com,
        baolin.wang@...ux.alibaba.com, zhuo.song@...ux.alibaba.com,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v1 2/3] drivers/perf: add DesignWare PCIe PMU driver

On Mon, Sep 26, 2022 at 09:31:34PM +0800, Shuai Xue wrote:
> 在 2022/9/23 PM11:54, Jonathan Cameron 写道:
> >> I found a similar definition in arch/ia64/pci/pci.c .
> >>
> >> 	#define PCI_SAL_ADDRESS(seg, bus, devfn, reg)		\
> >> 	(((u64) seg << 24) | (bus << 16) | (devfn << 8) | (reg))
> >>
> >> Should we move it into a common header first?
> > 
> > Maybe. The bus, devfn, reg part is standard bdf, but I don't think
> > the PCI 6.0 spec defined a version with the seg in the upper bits.
> > I'm not sure if we want to adopt that in LInux.
> 
> I found lots of code use seg,bus,devfn,reg with format "%04x:%02x:%02x.%x",
> I am not quite familiar with PCIe spec. What do you think about it, Bjorn?

The PCIe spec defines an address encoding for bus/device/function/reg
for the purposes of ECAM (PCIe r6.0, sec 7.2.2), but as far as I know,
it doesn't define anything similar that includes the segment.  The
segment is really outside the scope of PCIe because each segment is a
completely separate PCIe hierarchy.

So I probably wouldn't make this a generic definition.  But if/when
you print things like this out, please do use the format spec you
mentioned above so it matches the style used elsewhere.

Bjorn