[PATCH] drm/radeon: fix asic initialization for virtualized environments

[Alex Williamson]

On Mon, 13 Jun 2016 15:45:20 -0400
Alex Deucher <alexdeucher at gmail.com> wrote:

> When executing in a PCI passthrough based virtuzliation environment, the
> hypervisor will usually attempt to send a PCIe bus reset signal to the
> ASIC when the VM reboots. In this scenario, the card is not correctly
> initialized, but we still consider it to be posted. Therefore, in a
> passthrough based environemnt we should always post the card to guarantee
> it is in a good state for driver initialization.
> 
> Ported from amdgpu commit:
> amdgpu: fix asic initialization for virtualized environments
> 
> Cc: Andres Rodriguez <andres.rodriguez at amd.com>
> Cc: Alex Williamson <alex.williamson at redhat.com>
> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> Cc: stable at vger.kernel.org
> ---
>  drivers/gpu/drm/radeon/radeon_device.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)

Thanks, I expect it's an improvement, though it's always a bit
disappointing when a driver starts modifying its behavior based on
what might be a transient feature of the platform, in this case a
hypervisor platform.  For instance, why does our bus reset and video
ROM execution result in a different state than a physical BIOS doing
the same?  Can't this condition occur regardless of a hypervisor,
perhaps a rare hot-add of a GPU, a bare metal kexec reboot, or perhaps
simply a system BIOS optimized to post a limited set of devices.
Detection based on some state of the device rather than an expectation
based on what the device is running on seems preferable.  I suspect
Andres' patch for amdgpu only affects newer devices, which pretty much
all suffer reset issues, at least under QEMU/VFIO, but I wonder how this
patch affects existing working devices, like 6, 7, and some 8-series.
Anyway, if this is the solution to the poor behavior we've seen with
assigned AMD cards, maybe someone could request the same for the closed
drivers, including Windows.  Thanks,

Alex

> diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
> index e61c763..21c44b2 100644
> --- a/drivers/gpu/drm/radeon/radeon_device.c
> +++ b/drivers/gpu/drm/radeon/radeon_device.c
> @@ -630,6 +630,23 @@ void radeon_gtt_location(struct radeon_device *rdev, struct radeon_mc *mc)
>  /*
>   * GPU helpers function.
>   */
> +
> +/**
> + * radeon_device_is_virtual - check if we are running is a virtual environment
> + *
> + * Check if the asic has been passed through to a VM (all asics).
> + * Used at driver startup.
> + * Returns true if virtual or false if not.
> + */
> +static bool radeon_device_is_virtual(void)
> +{
> +#ifdef CONFIG_X86
> +	return boot_cpu_has(X86_FEATURE_HYPERVISOR);
> +#else
> +	return false;
> +#endif
> +}
> +
>  /**
>   * radeon_card_posted - check if the hw has already been initialized
>   *
> @@ -643,6 +660,10 @@ bool radeon_card_posted(struct radeon_device *rdev)
>  {
>  	uint32_t reg;
>  
> +	/* for pass through, always force asic_init */
> +	if (radeon_device_is_virtual())
> +		return false;
> +
>  	/* required for EFI mode on macbook2,1 which uses an r5xx asic */
>  	if (efi_enabled(EFI_BOOT) &&
>  	    (rdev->pdev->subsystem_vendor == PCI_VENDOR_ID_APPLE) &&