linux-kernel - Re: [PATCH V4 02/12] PCI: Add TPH related register definition

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Message-ID: <20240905164128.GA391042@bhelgaas>
Date: Thu, 5 Sep 2024 11:41:28 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Wei Huang <wei.huang2@....com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, netdev@...r.kernel.org,
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Subject: Re: [PATCH V4 02/12] PCI: Add TPH related register definition

On Thu, Sep 05, 2024 at 10:08:33AM -0500, Wei Huang wrote:
> On 9/4/24 14:52, Bjorn Helgaas wrote:
> >> -#define PCI_TPH_CAP_ST_MASK	0x07FF0000	/* ST table mask */
> >> -#define PCI_TPH_CAP_ST_SHIFT	16	/* ST table shift */
> >> -#define PCI_TPH_BASE_SIZEOF	0xc	/* size with no ST table */
> >> +#define  PCI_TPH_CAP_NO_ST	0x00000001 /* No ST Mode Supported */
> >> +#define  PCI_TPH_CAP_INT_VEC	0x00000002 /* Interrupt Vector Mode Supported */
> >> +#define  PCI_TPH_CAP_DEV_SPEC	0x00000004 /* Device Specific Mode Supported */
> > 
> > I think these modes should all include "ST" to clearly delineate
> > Steering Tags from the Processing Hints.  E.g.,
> > 
> >   PCI_TPH_CAP_ST_NO_ST       or maybe PCI_TPH_CAP_ST_NONE
> 
> Can I keep "NO_ST" instead of switching over to "ST_NONE"? First, it
> matches with PCIe spec. Secondly, IMO "ST_NONE" implies no ST support at
> all.

Sure.  Does PCI_TPH_CAP_ST_NO_ST work for you?  That follows the same
PCI_TPH_CAP_ST_* pattern as below.

> >   PCI_TPH_CAP_ST_INT_VEC
> >   PCI_TPH_CAP_ST_DEV_SPEC
> 
> Will change

> >> +#define  PCI_TPH_CAP_ST_MASK	0x07FF0000 /* ST Table Size */
> >> +#define  PCI_TPH_CAP_ST_SHIFT	16	/* ST Table Size shift */
> >> +#define PCI_TPH_BASE_SIZEOF	0xc	/* Size with no ST table */
> >> +
> >> +#define PCI_TPH_CTRL		8	/* control register */
> >> +#define  PCI_TPH_CTRL_MODE_SEL_MASK	0x00000007 /* ST Mode Select */
> >> +#define   PCI_TPH_NO_ST_MODE		0x0 /* No ST Mode */
> >> +#define   PCI_TPH_INT_VEC_MODE		0x1 /* Interrupt Vector Mode */
> >> +#define   PCI_TPH_DEV_SPEC_MODE		0x2 /* Device Specific Mode */
> > 
> > These are also internal, but they're new and I think they should also
> > include "ST" to match the CAP #defines.
> > 
> > Even better, maybe we only add these and use them for both CAP and
> > CTRL since they're defined with identical values.
> 
> Can you elaborate here? In CTRL register, "ST Mode Select" is defined as
> a 2-bit field. The possible values are 0, 1, 2. But in CAP register, the
> modes are individual bit masked. So I cannot use CTRL definitions in CAP
> register directly unless I do shifting.

Oops, sorry, I thought they were the same values, but they're not, so
ignore this comment.