linux-kernel - Re: [PATCH v11 10/23] CXL/AER: Update PCI class code check to use FIELD

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Message-ID: <0e3baee1-0909-489c-b6a1-1d64e988e16b@amd.com>
Date: Thu, 11 Sep 2025 13:18:57 -0500
From: "Bowman, Terry" <terry.bowman@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: dave@...olabs.net, dave.jiang@...el.com, alison.schofield@...el.com,
 dan.j.williams@...el.com, bhelgaas@...gle.com, shiju.jose@...wei.com,
 ming.li@...omail.com, Smita.KoralahalliChannabasappa@....com,
 rrichter@....com, dan.carpenter@...aro.org,
 PradeepVineshReddy.Kodamati@....com, lukas@...ner.de,
 Benjamin.Cheatham@....com, sathyanarayanan.kuppuswamy@...ux.intel.com,
 linux-cxl@...r.kernel.org, alucerop@....com, ira.weiny@...el.com,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v11 10/23] CXL/AER: Update PCI class code check to use
 FIELD_GET()



On 8/29/2025 11:03 AM, Jonathan Cameron wrote:
> On Tue, 26 Aug 2025 20:35:25 -0500
> Terry Bowman <terry.bowman@....com> wrote:
>
>> Update the AER driver's is_cxl_mem_dev() to use FIELD_GET() while checking
>> for a CXL Endpoint class code.
>>
>> Introduce a genmask bitmask for checking PCI class codes and locate in
>> include/uapi/linux/pci_regs.h.
>>
>> Update the function documentation to reference the latest CXL
>> specification.
>>
>> Signed-off-by: Terry Bowman <terry.bowman@....com>
> In general I like this change, but maybe we should make a broader use of
> it even in this introductory patch.  E.g. use FIELD_PREP()
> in cxl_mem_pci_tbl() and perhaps add a define for the mask
> of the programming interface as well?
>
> Maybe use it in pci_ids.h (which raises the question of whether
> it's in the right place) for PCI_CLASS_BRIDGE_PCI_NORMAL / SUBTRACTIVE
> and the various USB definitions that include the programming interface.
>
> Perhaps wider use is something for a follow up, but nice to at least
> use it everywhere relevant in the CXL code to make the justification stronger
> from the start.
I will add a TODO item to the list at a lower priority for replacing FIELD_GET with FIELD_PREP here.
>> ---
>> Changes in v10->v11:
>> - Add #include <linux/bitfield.h> to cxl_ras.c
> I think you missed and hit wrong file!

Yup, thanks.
>> - Removed line wrapping at "(CXL 3.2, 8.1.12.1)".
>> ---
>>  drivers/pci/pcie/aer.c        | 1 +
>>  drivers/pci/pcie/rch_aer.c    | 6 +++---
>>  include/uapi/linux/pci_regs.h | 2 ++
>>  3 files changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>> index 1b5f5b0cdc4f..ed1de9256898 100644
>> --- a/drivers/pci/pcie/aer.c
>> +++ b/drivers/pci/pcie/aer.c
>> @@ -30,6 +30,7 @@
>>  #include <linux/kfifo.h>
>>  #include <linux/ratelimit.h>
>>  #include <linux/slab.h>
>> +#include <linux/bitfield.h>
> This seems unrelated as no use of new stuff in here.
> Also, looks from what I can see here to be alphabetical order.
>
bitfield.h provides FIELD_GET() added below.

Terry
> .
>>  #include <acpi/apei.h>
>>  #include <acpi/ghes.h>
>>  #include <ras/ras_event.h>
>> diff --git a/drivers/pci/pcie/rch_aer.c b/drivers/pci/pcie/rch_aer.c
>> index bfe071eebf67..c3e2d4cbe8cc 100644
>> --- a/drivers/pci/pcie/rch_aer.c
>> +++ b/drivers/pci/pcie/rch_aer.c
>> @@ -17,10 +17,10 @@ static bool is_cxl_mem_dev(struct pci_dev *dev)
>>  		return false;
>>  
>>  	/*
>> -	 * CXL Memory Devices must have the 502h class code set (CXL
>> -	 * 3.0, 8.1.12.1).
>> +	 * CXL Memory Devices must have the 502h class code set
>> +	 * (CXL 3.2, 8.1.12.1).
>>  	 */
>> -	if ((dev->class >> 8) != PCI_CLASS_MEMORY_CXL)
>> +	if (FIELD_GET(PCI_CLASS_CODE_MASK, dev->class) != PCI_CLASS_MEMORY_CXL)
>>  		return false;
>>  
>>  	return true;
>> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
>> index 252c06402b13..c7b635f6cf36 100644
>> --- a/include/uapi/linux/pci_regs.h
>> +++ b/include/uapi/linux/pci_regs.h
>> @@ -73,6 +73,8 @@
>>  #define PCI_CLASS_PROG		0x09	/* Reg. Level Programming Interface */
>>  #define PCI_CLASS_DEVICE	0x0a	/* Device class */
>>  
>> +#define PCI_CLASS_CODE_MASK     __GENMASK(23, 8)
>> +
>>  #define PCI_CACHE_LINE_SIZE	0x0c	/* 8 bits */
>>  #define PCI_LATENCY_TIMER	0x0d	/* 8 bits */
>>  #define PCI_HEADER_TYPE		0x0e	/* 8 bits */