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

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Message-ID: <20250829170320.000010a3@huawei.com>
Date: Fri, 29 Aug 2025 17:03:20 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Terry Bowman <terry.bowman@....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 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.

> 
> ---
> Changes in v10->v11:
> - Add #include <linux/bitfield.h> to cxl_ras.c

I think you missed and hit wrong file!

> - 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.


>  #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 */