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

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Message-ID: <91a05b5b-a642-4cef-9c81-cba246435aa9@amd.com>
Date: Thu, 5 Sep 2024 10:08:33 -0500
From: Wei Huang <wei.huang2@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, netdev@...r.kernel.org,
 Jonathan.Cameron@...wei.com, corbet@....net, davem@...emloft.net,
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 Eric.VanTassell@....com, vadim.fedorenko@...ux.dev, horms@...nel.org,
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Subject: Re: [PATCH V4 02/12] PCI: Add TPH related register definition



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.

>   PCI_TPH_CAP_ST_INT_VEC
>   PCI_TPH_CAP_ST_DEV_SPEC

Will change

> 
>> +#define  PCI_TPH_CAP_EXT_TPH	0x00000100 /* Ext TPH Requester Supported */
>> +#define  PCI_TPH_CAP_LOC_MASK	0x00000600 /* ST Table Location */
>> +#define   PCI_TPH_LOC_NONE	0x00000000 /* Not present */
>> +#define   PCI_TPH_LOC_CAP	0x00000200 /* In capability */
>> +#define   PCI_TPH_LOC_MSIX	0x00000400 /* In MSI-X */
> 
> These are existing symbols just being tidied, so can't really add "ST"
> here unless we just add aliases.  Since they're just used internally,
> not by drivers, I think they're fine as-is.
> 

Yes. In V1 review, Alex Williamson and Jonathan Cameron asked not to
change these definitions as they might be used by existing software.

>> +#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.