linux-kernel - Re: [PATCH v3 1/2] PCI: Fix the wrong reading of register fields

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Message-ID: <alpine.DEB.2.21.2501221247290.27203@angie.orcam.me.uk>
Date: Wed, 22 Jan 2025 12:53:15 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Jiwei Sun <sjiwei@....com>
cc: ilpo.jarvinen@...ux.intel.com, Bjorn Helgaas <bhelgaas@...gle.com>, 
    linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, 
    helgaas@...nel.org, lukas@...ner.de, ahuang12@...ovo.com, 
    sunjw10@...ovo.com, jiwei.sun.bj@...com, sunjw10@...look.com
Subject: Re: [PATCH v3 1/2] PCI: Fix the wrong reading of register fields

> The macro PCIE_LNKCTL2_TLS2SPEED() and PCIE_LNKCAP_SLS2SPEED() just use
> the link speed field of the registers. However, there are many other
> different function fields in the Link Control 2 Register or the Link
> Capabilities Register. If the register value is directly used by the two
> macros, it may cause getting an error link speed value (PCI_SPEED_UNKNOWN).

 The change proposed seems right to me, however...

> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 2e40fc63ba31..c571f5943f3d 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -337,12 +337,14 @@ void pci_bus_put(struct pci_bus *bus);
>  
>  #define PCIE_LNKCAP_SLS2SPEED(lnkcap)					\
>  ({									\
> -	((lnkcap) == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT :	\
> -	 (lnkcap) == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT :	\
> -	 (lnkcap) == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT :	\
> -	 (lnkcap) == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT :	\
> -	 (lnkcap) == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT :	\
> -	 (lnkcap) == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT :	\
> +	u32 __lnkcap = (lnkcap) & PCI_EXP_LNKCAP_SLS;			\
> +									\
> +	(__lnkcap == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT :	\
> +	 __lnkcap == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT :	\
> +	 __lnkcap == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT :	\
> +	 __lnkcap == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT :	\
> +	 __lnkcap == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT :	\
> +	 __lnkcap == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT :	\

 ... wouldn't it make sense to give the intermediate variable a meaningful 
name reflecting data it carries, e.g. `lnkcap_sls'?

> @@ -357,13 +359,17 @@ void pci_bus_put(struct pci_bus *bus);
>  	 PCI_SPEED_UNKNOWN)
>  
>  #define PCIE_LNKCTL2_TLS2SPEED(lnkctl2) \
> -	((lnkctl2) == PCI_EXP_LNKCTL2_TLS_64_0GT ? PCIE_SPEED_64_0GT : \
> -	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_32_0GT ? PCIE_SPEED_32_0GT : \
> -	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_16_0GT ? PCIE_SPEED_16_0GT : \
> -	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_8_0GT ? PCIE_SPEED_8_0GT : \
> -	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_5_0GT ? PCIE_SPEED_5_0GT : \
> -	 (lnkctl2) == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT : \
> -	 PCI_SPEED_UNKNOWN)
> +({									\
> +	u16 __lnkctl2 = (lnkctl2) & PCI_EXP_LNKCTL2_TLS;		\
> +									\
> +	(__lnkctl2 == PCI_EXP_LNKCTL2_TLS_64_0GT ? PCIE_SPEED_64_0GT :	\
> +	 __lnkctl2 == PCI_EXP_LNKCTL2_TLS_32_0GT ? PCIE_SPEED_32_0GT :	\
> +	 __lnkctl2 == PCI_EXP_LNKCTL2_TLS_16_0GT ? PCIE_SPEED_16_0GT :	\
> +	 __lnkctl2 == PCI_EXP_LNKCTL2_TLS_8_0GT ? PCIE_SPEED_8_0GT :	\
> +	 __lnkctl2 == PCI_EXP_LNKCTL2_TLS_5_0GT ? PCIE_SPEED_5_0GT :	\
> +	 __lnkctl2 == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT :	\
> +	 PCI_SPEED_UNKNOWN);						\
> +})

 And likewise e.g. `lnkctl2_tls'?

  Maciej