Re: [PATCH v2 1/1] vpci: Add resizable bar support

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Dec 02, 2024 at 02:09:56PM +0800, Jiqian Chen wrote:
> Some devices, like discrete GPU of amd, support resizable bar
> capability, but vpci of Xen doesn't support this feature, so
> they fail to resize bars and then cause probing failure.
> 
> According to PCIe spec, each bar that supports resizing has
> two registers, PCI_REBAR_CAP and PCI_REBAR_CTRL. So, add
> handlers for them to support resizing the size of BARs.
> 
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> ---
> Hi all,
> 
> v2->v1 changes:
> *In rebar_ctrl_write, to check if memory decoding is enabled, and added
> some checks for the type of Bar.
> *Added vpci_hw_write32 to handle PCI_REBAR_CAP's write, since there is
> no write limitation of dom0.
> *And has many other minor modifications as well.
> 
> Best regards,
> Jiqian Chen.
> ---
>  xen/drivers/vpci/Makefile  |  2 +-
>  xen/drivers/vpci/rebar.c   | 93 ++++++++++++++++++++++++++++++++++++++
>  xen/drivers/vpci/vpci.c    |  6 +++
>  xen/include/xen/pci_regs.h | 11 +++++
>  xen/include/xen/vpci.h     |  2 +
>  5 files changed, 113 insertions(+), 1 deletion(-)
>  create mode 100644 xen/drivers/vpci/rebar.c
> 
> diff --git a/xen/drivers/vpci/Makefile b/xen/drivers/vpci/Makefile
> index 1a1413b93e76..a7c8a30a8956 100644
> --- a/xen/drivers/vpci/Makefile
> +++ b/xen/drivers/vpci/Makefile
> @@ -1,2 +1,2 @@
> -obj-y += vpci.o header.o
> +obj-y += vpci.o header.o rebar.o
>  obj-$(CONFIG_HAS_PCI_MSI) += msi.o msix.o
> diff --git a/xen/drivers/vpci/rebar.c b/xen/drivers/vpci/rebar.c
> new file mode 100644
> index 000000000000..156e8d337426
> --- /dev/null
> +++ b/xen/drivers/vpci/rebar.c
> @@ -0,0 +1,93 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Copyright (C) 2024 Advanced Micro Devices, Inc. All Rights Reserved.
> + *
> + * Author: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> + */
> +
> +#include <xen/hypercall.h>
> +#include <xen/vpci.h>
> +
> +static void cf_check rebar_ctrl_write(const struct pci_dev *pdev,
> +                                      unsigned int reg,
> +                                      uint32_t val,
> +                                      void *data)
> +{
> +    uint64_t size;
> +    unsigned int index;
> +    struct vpci_bar *bars = data;
> +
> +    if ( pci_conf_read16(pdev->sbdf, PCI_COMMAND) & PCI_COMMAND_MEMORY )
> +        return;
> +
> +    index = pci_conf_read32(pdev->sbdf, reg) & PCI_REBAR_CTRL_BAR_IDX;
> +    if ( index >= PCI_HEADER_NORMAL_NR_BARS )
> +        return;
> +
> +    if ( bars[index].type != VPCI_BAR_MEM64_LO &&
> +         bars[index].type != VPCI_BAR_MEM32 )
> +        return;

For those early returns that don't propagate the write to the
register, we need to log a message to notice the write has been
dropped, otherwise there's no way to identify such cases.

Thanks, Roger.