linux-kernel - Re: [PATCH] PCI: Add PCI_EXP_DEVCTL_PAYLOAD

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Message-ID: <20210412192740.GA2151026@bjorn-Precision-5520>
Date:   Mon, 12 Apr 2021 14:27:40 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Add PCI_EXP_DEVCTL_PAYLOAD_* macros

On Mon, Apr 12, 2021 at 02:46:02PM +0200, Pali Rohár wrote:
> Define new PCI_EXP_DEVCTL_PAYLOAD_* macros in linux/pci_regs.h header file
> for Max Payload Size. Macros are defined in the same style as existing
> macros PCI_EXP_DEVCTL_READRQ_* macros.
> 
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>  include/uapi/linux/pci_regs.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index e709ae8235e7..8f1b15eea53e 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -504,6 +504,12 @@
>  #define  PCI_EXP_DEVCTL_URRE	0x0008	/* Unsupported Request Reporting En. */
>  #define  PCI_EXP_DEVCTL_RELAX_EN 0x0010 /* Enable relaxed ordering */
>  #define  PCI_EXP_DEVCTL_PAYLOAD	0x00e0	/* Max_Payload_Size */
> +#define  PCI_EXP_DEVCTL_PAYLOAD_128B 0x0000 /* 128 Bytes */
> +#define  PCI_EXP_DEVCTL_PAYLOAD_256B 0x0020 /* 256 Bytes */
> +#define  PCI_EXP_DEVCTL_PAYLOAD_512B 0x0040 /* 512 Bytes */
> +#define  PCI_EXP_DEVCTL_PAYLOAD_1024B 0x0060 /* 1024 Bytes */
> +#define  PCI_EXP_DEVCTL_PAYLOAD_2048B 0x0080 /* 2048 Bytes */
> +#define  PCI_EXP_DEVCTL_PAYLOAD_4096B 0x00A0 /* 4096 Bytes */

This is fine if we're going to use them, but we generally don't add
definitions purely for documentation.

5929b8a38ce0 ("PCI: Add defines for PCIe Max_Read_Request_Size") added
the PCI_EXP_DEVCTL_READRQ_* definitions and we do have a few (very
few) uses in drivers.

If we do need to add these, please follow the local use of lower-case
in the hex bitmasks.  The file is a mixture, but the closest examples
are lower-case.

>  #define  PCI_EXP_DEVCTL_EXT_TAG	0x0100	/* Extended Tag Field Enable */
>  #define  PCI_EXP_DEVCTL_PHANTOM	0x0200	/* Phantom Functions Enable */
>  #define  PCI_EXP_DEVCTL_AUX_PME	0x0400	/* Auxiliary Power PM Enable */
> -- 
> 2.20.1
>