Re: [Xen-devel] [PATCH 2/2] xen-pciback: Allow enabling/disabling expansion ROM

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

On Sun, Dec 02, 2018 at 06:47:33PM +0100, Marek Marczykowski-Górecki wrote:
> From: Dwayne Litzenberger <dlitz@xxxxxxxxx>
> 
> Newer AMD GPUs store their initialization routines as bytecode on the
> ROM.  This fixes the following initialization error inside the VM when
> doing PCI passthrough:
> 
>     radeon 0000:00:05.0: Invalid PCI ROM header signature: expecting 0xaa55, 
> got 0xffff
>     radeon 0000:00:05.0: Invalid PCI ROM header signature: expecting 0xaa55, 
> got 0xffff
>     [drm:radeon_get_bios [radeon]] *ERROR* Unable to locate a BIOS ROM
>     radeon 0000:00:05.0: Fatal error during GPU init
> 
> Signed-off-by: Dwayne Litzenberger <dlitz@xxxxxxxxx>
> ---
>  drivers/xen/xen-pciback/conf_space_header.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/xen/xen-pciback/conf_space_header.c 
> b/drivers/xen/xen-pciback/conf_space_header.c
> index 697d0a8..bc145d3 100644
> --- a/drivers/xen/xen-pciback/conf_space_header.c
> +++ b/drivers/xen/xen-pciback/conf_space_header.c
> @@ -150,21 +150,21 @@ static int rom_write(struct pci_dev *dev, int offset, 
> u32 value, void *data)
>       if ((value | ~PCI_ROM_ADDRESS_MASK) == ~0U)
>               bar->which = 1;
>       else {
> -             u32 tmpval;
> -             err = pci_read_config_dword(dev, offset, &tmpval);
> +             u32 newval = bar->val;

Naming this newval is quite confusing IMO, since at this point it's
actually the old value.

> +
> +             /* Allow enabling/disabling rom, if present */
> +             if (newval & PCI_ROM_ADDRESS_MASK) {
> +                     newval &= ~PCI_ROM_ADDRESS_ENABLE;
> +                     newval |= value & PCI_ROM_ADDRESS_ENABLE;
> +             }
> +             err = pci_write_config_dword(dev, offset, newval);
>               if (err)
>                       goto out;
> -             if (tmpval != bar->val && value == bar->val) {
> -                     /* Allow restoration of bar value. */
> -                     err = pci_write_config_dword(dev, offset, bar->val);
> -                     if (err)
> -                             goto out;
> -             }
> +             bar->val = newval;

I'm not sure there's much value in storing this, the only difference
is the setting of the enable bit, which is ignored anyway.

Thanks, Roger.

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