[PATCH] amdgpu: resize BAR0 to the maximum available size, even if it doesn't cover VRAM

[Christian König]

Am 10.12.20 um 01:57 schrieb Darren Salt:
> This allows BAR0 resizing to be done for cards which don't advertise support
> for a size large enough to cover the VRAM but which do advertise at least
> one size larger than the default. For example, my RX 5600 XT, which
> advertises 256MB, 512MB and 1GB.

I've never seen such a configuration except for engineering samples. Can 
you send me a dump of the relevant PCI configuration space?

In general we could do this, but instead of just blindly trying 
different values we should just pick a supported one in the first place.

Regards,
Christian.

>
> Signed-off-by: Darren Salt <devspam at moreofthesa.me.uk>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 44 +++++++++++++++++-----
>   1 file changed, 35 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> index 355fa0057c26..ec3610b4110b 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> @@ -1078,6 +1078,11 @@ void amdgpu_device_wb_free(struct amdgpu_device *adev, u32 wb)
>   		__clear_bit(wb, adev->wb.used);
>   }
>   
> +static inline u32 bytes_to_size_pci(u64 bytes)
> +{
> +	return order_base_2(((bytes >> 20) | 1)) - 1;
> +}
> +
>   /**
>    * amdgpu_device_resize_fb_bar - try to resize FB BAR
>    *
> @@ -1090,20 +1095,25 @@ void amdgpu_device_wb_free(struct amdgpu_device *adev, u32 wb)
>   int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
>   {
>   	u64 space_needed = roundup_pow_of_two(adev->gmc.real_vram_size);
> -	u32 rbar_size = order_base_2(((space_needed >> 20) | 1)) - 1;
> +	u32 rbar_size = bytes_to_size_pci(space_needed);
>   	struct pci_bus *root;
>   	struct resource *res;
> +	u64 current_bytes;
> +	u32 current_size;
>   	unsigned i;
>   	u16 cmd;
>   	int r;
> +	bool nospc = false;
>   
>   	/* Bypass for VF */
>   	if (amdgpu_sriov_vf(adev))
>   		return 0;
>   
> -	/* skip if the bios has already enabled large BAR */
> -	if (adev->gmc.real_vram_size &&
> -	    (pci_resource_len(adev->pdev, 0) >= adev->gmc.real_vram_size))
> +	current_bytes = pci_resource_len(adev->pdev, 0);
> +	current_size = bytes_to_size_pci(current_bytes);
> +
> +	/* Skip if the BIOS has already enabled large BAR, covering the VRAM */
> +	if (current_size >= rbar_size)
>   		return 0;
>   
>   	/* Check if the root BUS has 64bit memory resources */
> @@ -1121,6 +1131,9 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
>   	if (!res)
>   		return 0;
>   
> +	dev_dbg(adev->dev, "BIOS-allocated BAR0 was %lluMB; trying to get %lluMB",
> +	        current_bytes >> 20, space_needed >> 20);
> +
>   	/* Disable memory decoding while we change the BAR addresses and size */
>   	pci_read_config_word(adev->pdev, PCI_COMMAND, &cmd);
>   	pci_write_config_word(adev->pdev, PCI_COMMAND,
> @@ -1133,11 +1146,24 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
>   
>   	pci_release_resource(adev->pdev, 0);
>   
> -	r = pci_resize_resource(adev->pdev, 0, rbar_size);
> -	if (r == -ENOSPC)
> -		DRM_INFO("Not enough PCI address space for a large BAR.");
> -	else if (r && r != -ENOTSUPP)
> -		DRM_ERROR("Problem resizing BAR0 (%d).", r);
> +	while (rbar_size > current_size) {
> +		r = pci_resize_resource(adev->pdev, 0, rbar_size);
> +		if (r == 0 || r == -ENOTSUPP) {
> +			break;
> +		} else if (r == -ENOSPC) {
> +			if (!nospc) {
> +				/* Warn only the first time */
> +				dev_info(adev->dev, "Not enough PCI address space for a large BAR.");
> +				nospc = true;
> +			}
> +			--rbar_size;
> +		} else if (r == -EINVAL) {
> +			--rbar_size;
> +		} else {
> +			dev_err(adev->dev, "Problem resizing BAR0 (%d).", r);
> +			break;
> +		}
> +	}
>   
>   	pci_assign_unassigned_bus_resources(adev->pdev->bus);
>