Re: [PATCH] PCI: vmd: Fix domain reset operation

Bjorn Helgaas
2023-06-20T18:07:51Z

On Tue, May 30, 2023 at 02:47:06PM -0700, Nirmal Patel wrote:
> During domain reset process we are accidentally enabling
> the prefetchable memory by writing 0x0 to Prefetchable Memory
> Base and Prefetchable Memory Limit registers. As a result certain
> platforms failed to boot up.
>
> Here is the quote from section 7.5.1.3.9 of PCI Express Base 6.0 spec:
>
> The Prefetchable Memory Limit register must be programmed to a smaller
> value than the Prefetchable Memory Base register if there is no
> prefetchable memory on the secondary side of the bridge.
>
> When clearing Prefetchable Memory Base, Prefetchable Memory
> Limit and Prefetchable Base Upper 32 bits, the prefetchable
> memory range becomes 0x0-0x575000fffff. As a result the
> prefetchable memory is enabled accidentally.
>
> Implementing correct operation by writing a value to Prefetchable
> Base Memory larger than the value of Prefetchable Memory Limit.

Oh, I forgot: better to use imperative mood here instead of present
participle ("-ing" form), e.g., "Write ... so that ..."

This should probably use the same form as pci_disable_bridge_window(),
since I think it's doing the same thing.

> Signed-off-by: Nirmal Patel <nirmal.patel@linux.intel.com>
> ---
> drivers/pci/controller/vmd.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 769eedeb8802..f3eb740e3028 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -526,8 +526,18 @@ static void vmd_domain_reset(struct vmd_dev *vmd)
> PCI_CLASS_BRIDGE_PCI))
> continue;
>
> - memset_io(base + PCI_IO_BASE, 0,
> - PCI_ROM_ADDRESS1 - PCI_IO_BASE);
> + writel(0, base + PCI_IO_BASE);
> + writew(0xFFF0, base + PCI_MEMORY_BASE);
> + writew(0, base + PCI_MEMORY_LIMIT);
> +
> + writew(0xFFF1, base + PCI_PREF_MEMORY_BASE);
> + writew(0, base + PCI_PREF_MEMORY_LIMIT);
> +
> + writel(0xFFFFFFFF, base + PCI_PREF_BASE_UPPER32);
> + writel(0, base + PCI_PREF_LIMIT_UPPER32);
> +
> + writel(0, base + PCI_IO_BASE_UPPER16);
> + writeb(0, base + PCI_CAPABILITY_LIST);
> }
> }
> }
> --
> 2.27.0
>