linux-kernel - Re: [PATCH v3] PCI: Update Resizable BAR Capability Register fields

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Message-ID: <74418233-2fec-435e-aada-d4505b34bc8c@amd.com>
Date: Thu, 20 Feb 2025 10:18:00 +0100
From: Christian König <christian.koenig@....com>
To: Zhiyuan Dai <daizhiyuan@...tium.com.cn>, helgaas@...nel.org
Cc: bhelgaas@...gle.com, linux-kernel@...r.kernel.org,
 linux-pci@...r.kernel.org
Subject: Re: [PATCH v3] PCI: Update Resizable BAR Capability Register fields

Am 20.02.25 um 02:30 schrieb Zhiyuan Dai:
> PCI Express Base Spec r6.0 defines BAR size up to 8 EB (2^63 bytes),
> but supporting anything bigger than 128TB requires changes to pci_rebar_get_possible_sizes()
> to read the additional Capability bits from the Control register.
>
> If 8EB support is required, callers will need to be updated to handle u64 instead of u32.
> For now, support is limited to 128TB, and support for sizes greater than 128TB can be
> deferred to a later time.
>
> Signed-off-by: Zhiyuan Dai <daizhiyuan@...tium.com.cn>

Reviewed-by: Christian König <christian.koenig@....com>

> ---
>  drivers/pci/pci.c             | 4 ++--
>  include/uapi/linux/pci_regs.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 661f98c6c63a..77b9ceefb4e1 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3752,7 +3752,7 @@ static int pci_rebar_find_pos(struct pci_dev *pdev, int bar)
>   * @bar: BAR to query
>   *
>   * Get the possible sizes of a resizable BAR as bitmask defined in the spec
> - * (bit 0=1MB, bit 19=512GB). Returns 0 if BAR isn't resizable.
> + * (bit 0=1MB, bit 31=128TB). Returns 0 if BAR isn't resizable.
>   */
>  u32 pci_rebar_get_possible_sizes(struct pci_dev *pdev, int bar)
>  {
> @@ -3800,7 +3800,7 @@ int pci_rebar_get_current_size(struct pci_dev *pdev, int bar)
>   * pci_rebar_set_size - set a new size for a BAR
>   * @pdev: PCI device
>   * @bar: BAR to set size to
> - * @size: new size as defined in the spec (0=1MB, 19=512GB)
> + * @size: new size as defined in the spec (0=1MB, 31=128TB)
>   *
>   * Set the new size of a BAR as defined in the spec.
>   * Returns zero if resizing was successful, error code otherwise.
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index 1601c7ed5fab..ce99d4f34ce5 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -1013,7 +1013,7 @@
>  
>  /* Resizable BARs */
>  #define PCI_REBAR_CAP		4	/* capability register */
> -#define  PCI_REBAR_CAP_SIZES		0x00FFFFF0  /* supported BAR sizes */
> +#define  PCI_REBAR_CAP_SIZES		0xFFFFFFF0  /* supported BAR sizes */
>  #define PCI_REBAR_CTRL		8	/* control register */
>  #define  PCI_REBAR_CTRL_BAR_IDX		0x00000007  /* BAR index */
>  #define  PCI_REBAR_CTRL_NBAR_MASK	0x000000E0  /* # of resizable BARs */